FLORIDA SPRAY GUN
FOR PINE TREE GUM FLOW STIMULATION
NORMAN BOURKE, M.E.
Associate Research Engineer
University of Florida
KEITH W. DORMAN, B.S.
Southern Forest Experiment Station
yr -$) 3(91 Z
Bulletin of the,
COLLEGE OF ENGINEERING
UNIVERSITY OF FLORIDA
FLORIDA ENGINEERING AND INDUSTRIAL EXPERIMENT STATION
Bulletin No. 10. March. 1946
The Florida Engineering and Industrial
The Engineering Experiment Station was first approved by
the Board of Control at its meeting on May 18, 1929. Funds
for the Florida Engineering and Industrial Experiment Station
-were appropriated by the Legislature of the State of Florida in
1941. The Station is a Division of the College of Engineering
of the University of Florida under the supervision of the State
Board of Control of Florida. The functions of the Engineering
and Industrial Experiment Station are:
a) To develop the industries of Florida by organizing and
promoting research in those fields of engineering, and the re-
lated sciences, bearing on the industrial welfare of the State.
b) To survey and evaluate the natural resources of the
State that may be susceptible to sound development.
c) To contact with governmental bodies, technical societies,
associations, or industrial organizations in aiding them to solve
their technical problems. Provision is made for these organ-
izations to avail themselves of the facilities of the Engineering
and Industrial Experiment Station on a co-operative financial
basis. It is the basic philosophy of the Station that the indus-
trial progress of Florida can best be further by carrying on
research in those fields in which Florida, by virtune of its loca-
tion, climate, and raw materials, has natural advantages.
d) To publish and disseminate information on the results
of experimental and research projects. Two series of pamphlets
are issued: Bulletins covering the results of research and in-
vestigations by staff members; and Technical Papers, reprinting
papers or reports by staff members which have been published
For copies of Bulletins, Technical Papers or information on
how the Station can be of service, address:
The Florida Engineering and Industrial Experiment Station
College of Engineering
University of Florida
JOSEPH WEL, Director
PUBLICATIONS OF THE FLORIDA
ENGINEERING AND INDUSTRIAL EXPERIMENT STATION
As long as the supply is adequate, copies of available publi-
cations are free for general distribution. Address all requests
to: The Director, Florida Engineering and Industrial Experi-
ment Station, University of Florida, Gainesville, Florida.
No. 1 "The Mapping Situation in Florida", by William L. Sawyer.
No. 2 "The Electrical Industry in Florida", by John W. Wilson.
No. 3 "The Locating of Tropical Storms by Means of Associated
Static", by Joseph Weil and Wayne Mason.
No. 4 "Study of Beach Conditions at Daytona Beach, Florida,
and Vicinity", by W. W. Fineren.
No. 5 "Climatic Data for the Design and Operation of Air Con-
ditioning Systems in Florida", by N. C. Ebaugh and
S. P. Goethe.
No. 6 "On Static Emanating from Six Tropical Storms and Its
Use in Locating the Position of the Disturbance", by
S. P. Sashoff and Joseph Weil.
No. 7 "Lime Rock Concrete- Part 1", by Harry H. Houston
and Ralph A. Morgen.
No. 8 "An Industrial Survey of Hides and Skins in Florida", by
William D. May.
No. 9 "Studies on Intermittent Sand Filtration of Sewage -
Part I", by D L. Emerson, Jr.
No. 10 "Florida Spray Gun for Pine Tree Gum Flow Stimula-
tion", by Norman Bourke and Keith W. Dorman.
TECHNICAL PAPER SERIES
No. 1 Heats of Solution of the System Sulfur Trioxide and
Water, by Ralph A. Morgen.
No. 2 The Useful Life of Pyro-Meta and Tetraphosphate, by
Ralph A. Morgen and Robert L. Swoope.
No. 3. Florida Lime Rock as an Admixture in Mortar and Con-
crete, by Harry H. Houston and Ralph A. Morgen.
No. 4 Country Hides and Skins, by William D. May.
No. 5 An Empirical Correction for Compressibility Factor and
Activity Coefficient Curves, by Ralph A. Morgen and
J. Howard Childs.
No. 6 Crate Closing Device, by William T. Tiffin.
No. 7 The System Sodium Acetate Sodium Hydroxide -
Water, by Ralph A. Morgen and R. D. Walker, Jr.
Florida Engineering and Industrial Experiment Station
University of Florida
Southern Forest Experiment Station
(Lake City, Fla., Branch)
United States Department of Agriculture
Bulletin No. 10
FLORIDA SPRAY GUN
TREE GUM FLOW STIMULATION
NORMAN BOURKE, M.E.
Associate Research Engineer
University of Florida
KEITH W. DORMAN, B.S.
Southern Forest Experiment Station
COLLEGE OF ENGINEERING
UNIVERSITY OF FLORIDA
The gum naval stores industry is one of the oldest industries
of Florida and the other Southeastern States. Its continued
well being is of great economic importance to the region. Any
contribution which will increase production with a saving in
labor costs is of value to that industry. The information in
this bulletin is directed towards accomplishing these two ob-
The industry includes a large number of comparatively small
individual operators. The results of this research will there-
fore benefit a large number of individuals as well as the indus-
try as a whole. The work on chemical stimulation was started
by the Southern Forest Experiment Station of the United States
Department of Agriculture over ten years ago. The detailed
results have been published elsewhere but a summary appears
here as Appendix I.
Cooperative ventures such as the one reported in this bul-
letin show how different agencies can work together to achieve
a common end. The Southern Forest Experiment Station is
interested in any improvement in the forest resources of the
region. The Florida Engineering and Industrial Experiment
Station conducts research for the betterment of the industries
of Florida. In this project the specialized techniques on the
sciences of forestry of one group combined with the engineering
skills of the other have resulted in a cooperative solution to a
problem which neither group, by itself, could have accomplished
It is hoped that this work will point the way to the solution
of more industrial problems of Florida by cooperation with
other interested groups.
JOSEPH WEBL, Director
TABLE OF CONTENTS
F orew ord .... .. .......... .......................... ....... . .. ..... .......... 2
Section I. Evolution of the Gun ........ .... ................................... 5
Introduction ........... .................. ---.... ........ .... ........ 5
"Acid Stimulation" Spray Gun Requirements ......... ..................... 6
Spray Gun Theory ..... .. ............. ....... .... . .- ---- ........................... 7
Development of the Florida Spray Gun ....................................... 10
Commercial Production ........ ..... . .................................. -17
Technical Test Data .......................... ......... ......................... ............... 19
Section II. Performance of the Florida Spray Guns During the 1945
Season ......... .... ................. ... ......................... 26
Appendix I. History of the Development of Chemical Stimulation ...... 29
Appendix II Resume of Other Devices Used for Acid Application........ 35
THE FLORIDA SPRAY GUN
U. S. Patent No. 2394424
FLORIDA SPRAY GUN
FOR PINE TREE GUM FLOW STIMULATION
EVOLUTION OF THE GUN
In December of 1943 the Florida Engineering and Industrial
Experiment Station was requested by the Southern Forest Ex-
periment Station I to assist in the development of a special type
spray gun. This instrument was urgently needed by the naval
stores industry to implement new methods developed in the ex-
perimental work at the Forest Experiment Station.
This special gun was needed to spray small amounts of
sulphuric acid on freshly cut wounds in slash or longleaf pines
(Pinus caribaea Morelet, Pinus palustris Mill.), made during
turpentining operations. Oleoresin, or "gum", exudes from
these wounds, which must be reopened, or "chipped", at inter-
vals of about one week to renew the flow. It was found that a
small amount of acid sprayed on a freshly cut "streak" ac-
celerated and prolonged the flow of gum.
The pioneering research work in the chemical stimulation
of gum yields of slash and longleaf pines was instituted by the
Southern Forest Experiment Station just ten years ago. Since
that time enormous strides have been made in developing vari-
ous techniques for the use of industry. One of the big problems
encountered was the development of suitable apparatus for
applying the chemical.
In the early years of the work those who applied chemicals
struggled along with brushes and swabs which proved totally
inadequate for the purpose because of the destructive properties
of sulphuric acid, (the chemical found to be the best of many
tested for increasing yields). In spite of shortages of critical
materials, a metal spray gun was developed as a stop-gap meas-
'Lake City, Fla. Branch of the Southern Forest Experiment Station,
Forest Service, United States Department of Agriculture.
ure. Because of metal break-downs, resulting from corrosion
by the acid, this gun was of limited usefulness. It was at this
point that the Florida Engineering and Industrial Experiment
Station learned of the problem and offered its cooperation.
"ACID-STIMULATION" SPRAY GUN REQUIREMENTS
The Southern Forest Experiment Station had evolved, in
the course of its experimental work, a very definite conception
of the features essential to a completely satisfactory spray gun
for acid application. It should be constructed throughout of
acid resistant materials. It should be simple in design, and
easy to disassemble for cleaning. The spray it delivers should
be proportioned in length and width so as exactly to cover the
freshly cut streak when the spray nozzle is held at a convenient
distance. It should cover the horizontal under surface of the
bark overhang as well as the vertical surface of the streak itself.
It should be adequate in amount to the absorptive powers of
the wood, for otherwise the maximum benefit of the treatment
would not be obtained. There should be no excess to run off
with the gum, as this would corrode the gutter and cup. The
spray should not be so fine as to be readily wind-blown upon the
operator. No acid should drip from the nozzle between appli-
cations. In short, all the deficiencies present In the devices
previously employed should be removed or corrected.
The ideal spray gun, as conceived by the Southern Forest
Experiment Station, would be incorporated in the "hack" used
in chipping the trees. The handle of the hack would be hollowed
and would contain an acid reservoir, a spray nozzle would be
fitted in the head and a suitable trigger would be provided.
In service the operator would first chip and then spray the
streak, all with the same instrument, without the necessity of
laying aside one tool and picking up another. Definite economies
in operation, it was believed, would be obtained with such a
dual purpose instrument.
The time element was, however, important. It was essential
that experimental models of any new development be given
extensive field tests during the 1944 production season, and the
final design be in commercial production and available to naval
stores producers for the 1945 season. The Forest Service con-
sidered the combined spray-gun-hack to be the ultimate ideal
instrument, but appreciated the fact that time would be required
for its development. Their immediate need, however, was
urgent, and any device which would produce a satisfactory spray
and stand up for a reasonable length of time would be accept-
able as a "stop-gap", provided that the primary objective of
commercial production of guns for the 1945 season was attained.
SPRAY GUN THEORY
The devices employed for the creation of a liquid spray fall,
in general, into two classes. In the first, which may be termed
mechanical atomization, an axial rotation is imparted to a solid
liquid jet emerging from an orifice, and this axial rotation,
through centrifugal force, causes the jet to increase in diameter
as it progresses, thereby breaking it into a spray of fine drop-
lets. (See Fig. 1.) The emerging spray is cone shaped. The
size of the droplets, and also the cone angle, is established by
both the absolute and the relative rotational and axial velocities,
by the diameter of the jet, and by the physical properties
(specific gravity, viscosity and surface tension) of the liquid.
The size of the droplets is not uniform across the section of the
spray cone, but increases progressively from center to edge, so
that the jet is composed of a central core of comparatively coarse
droplets surrounded by an envelope of finer ones. The axial
rotation of the jet is created by a mechanical device incorpor-
ated in the nozzle (Fig. la), or by a predirected motion in the
antechamber preceding the orifice (Fig. Ib). The character
of the spray may be modified, within limits, by appropriate
change in the dimensions of the nozzle.
In the second class, which may be termed air atomization,
a high velocity jet of air impinges on an emerging jet of liquid,
creating a sharp change in velocity of the liquid at the line of
impingement and thereby breaking the jet into a succession of
droplets. (See Fig. 2.) The shape of the resultant spray is
largely established by the natural shape of the air jet, which
may be widely varied but which is usually conical. The size of
the droplets is established by the absolute and relative velocities
of the air and liquid streams, and by the physical properties of
the liquid. The droplets vary in size, but not progressively
across the spray as in mechanical atomization, although the
coarser particles are more numerous towards the center. As
before, the character of the spray may be modified by change
in the dimensions of the nozzle.
F- -. -
MECHANICAL ATOMIZATION NOZZLES
In (a), the spiral guides create a rotation of the liquid stream which
causes the jet to expand and break into a spray. In (b), the tangential
entrance of the liquid creates a vortex in the antechamber and produces
the rotation of the stream which creates the spray.
In mechanical atomization nozzles a high pressure, ranging
from 8 to 1000 p.s.i. in various applications and services, is
required to force the liquid through the small and tortuous
passages. This pressure may be created by a liquid pump or
by a volume of compressed air confined above the surface of the
liquid in an enclosed reservoir. The former method is favored
for stationary installations and the latter is especially adapted
FMnw furnishd by courtesy of Sprayin Sytms Nzzlesa. Chikao. IB
fn & W GF vlr T w
to portable equipment. For intermittent service, as in the par-
ticular case under consideration, the timing of the discharge
may be controlled by a trigger operated valve immediately pre-
ceding the nozzle. In pump pressure types for intermittent
service, if the quantities per single discharge are small and
if the pressures required to produce the desired spray are mod-
erate, the stroke of the pump may be created by the motion of
a long-travel trigger or similar one-hand device, the discharge
persisting as long as the trigger is pulled. Both of these types
of discharge regulation and pressure creation are adapted to the
ideal spray-gun-hack conceived by the Forest Service.
AIR ATOMIZATION NOZZLE
The air pressure and velocity are greater than the liquid, and break the
solid liquid jet into a succession of droplets.
In air atomization nozzles, a considerable volume of low
pressure air is required. A portion of this air is usually di-
verted to the enclosed liquid reservoir and serves to deliver the
liquid to the nozzle. In shop and bench work the source of the
air is usually a stationary air compressor, but for field service
a portable compressor or hand pump is required. For inter-
mittent service the timing of the discharge may be regulated
by the stroke of this pump. Owing to the relatively large volume
of air required per discharge, however, a trigger-actuated pump
plunger is not practical, as the length of stroke is beyond the
SFisrure furnished by courtesy of Spraying Systems Noules. Chicago. III.
range of finger movement. A long-stroke pump requiring two
hands for its operation might conceivably be incorporated in
a hack, but would be unwieldy and probably unsatisfactory.
Pump, reservoir and nozzle can readily be combined into a single
unit (as may be seen in the numerous spray guns for insecti-
cide on the market), but the two-handed operation of such a
gun would necessitate the laying down of the hack while the
spray was being applied and this was definitely objectionable.
From a commercial production point of view, and particu-
larly for a speedily inaugurated production, air atomization
was the most attractive alternative. The guns would be simpler
in design, contain fewer parts and require less precision in
manufacture. The pressures would be lower and the construc-
tion less rugged. Most of the parts could be constructed of
glass or plastic, whereas critical high-priority corrosion re-
sistant metals would be required throughout for mechanical
atomization. Further, and this consideration was important,
it would simplify the task of finding a manufacturer with the
essential facilities who Was not already completely occupied
with other production.
THE DEVELOPMENT OF THE "FLORIDA" SPRAY GUN
At about this stage in the preliminary discussions, it was
suggested that in view of the small quantity and low pressure
of the air for this specific application the operator's lungs might
be substituted for the customary hand pump. The idea offered
two attractive potentialities. In the first place, two-handed
operation of the gun would be eliminated. Only one hand would
be required to hold such a gun and aim it at the streak, freeing
the other to retain the hack. (See Fig. 13.) The gun would
now be of bulk and proportions adapted to a shoulder sling or
belt holster, thus permitting the use of both hands in wielding
the hack and simplifying the problem of transportation. In
the second place, the pump would be eliminated from the manu-
factured assembly, reducing the number of manufacturing oper-
ations and the quantity of construction materials. Production
would be facilitated and the cost of the gun reduced.
In service, the operator would place the end of a short length
of flexible tubing in his mouth, aim the nozzle at the streak,
and blow. A certain degree of hazard would accompany this
operation, as suction applied to the tube might introduce acid
instructedd of Iown or drawn glass. Air from the operator's lungs
forces the ;cid up the central luli and out through the acid orifice. Air
also blows from the annular air orilice andl creates a spray. The glass
orifices were dliflicult to adjust and easily daima;ged.
vapor or liquid to the operator's mouth, but the hazard could
be minimized by appropriate design. It was, moreover, a hazard
more apparent than real, as it was rather improbable that
suction instead of pressure would be applied.
Offsetting the attractive features of the proposal was the
unconventionality of the idea. It was, nevertheless, tentatively
accepted. A glass model incorporating the principle was accord-
ingly designed and constructed. (See Fig. 3.) In this model
the nozzle was formed of two concentric tapered glass tubes,
providing a central orifice for the acid and a surrounding an-
nular ring for the air. It was designed to deliver '/2 cc. of acid
in 5 seconds when supplied with 36 cu. in. of air at 10 inches of
water static pressure. The rate of acid discharge was that
specified by the Southern Forest Experiment Station; the air
supply was that established experimentally at the University
as the lung capacity of an average man. Because of the limita-
tions of the material (glass) and the method of fabrication
(glass-blowing), the computed dimensions were realized only
approximately in construction and the orifices were not exactly
concentric. In laboratory tests, however, the model delivered
a fairly good spray, although at an excessive air pressure
In field tests at the Southern Forest Experiment Station the
results were considered promising. The spray cone angle was
excessive and the spray ragged, but the spray was nevertheless
comparable or superior to that produced by other guns then in
use and its imperfections were manifestly due, in part at least,
to its crude construction. The nozzle could not be brought as
closely to the streak as desired, and the spray could not be di-
rected upward against the bark overhang of the slash. The
air pressure was more than the laboratory tests had indicated.
All these were deficiencies which could be corrected by better
design and construction. The one-handed operation proved to
be quite practical. The basic principle of the device was accord-
ingly approved for further development.
In the light of this experience a second model was con-
structed. (See Fig. 4.) This one was of an acid resistant
vinylidene chloride polymer 2 of which a supply was then avail-
able. The design of the model was adapted to the form of the
:"Saran", manufactured by the Dow Chemical Co.
Nozzle constructed of plastic with improved air and acid orifices. The
best slope of the air passage, and the correct position of the acid orifice,
were determined by expe.-iment. The nozzle is mounted at the end of an
upward sloping arm, in order to direct the spray close against the streak
and the bark overhang.
material, viz. 1/4", i/" and 1" rods, and to the machine tools
available in the University Shops, but followed the same lines
as the first model. In this case, however, precision machining
to specified dimensions was possible, so the proportions of the
nozzle could be varied at will and the effect of modifications ex-
perimentally observed. Various dimensional combinations were
tested, of which the one shown in Fig. 4 was considered the
best. In these tests it was observed that although the spray
was very sensitive to small dimensional changes in the nozzle,
it was most profoundly influenced by the axial location of the
air and acid orifices, indicating that in the final design an auto-
matic precision positioning of these orifices should be provided.
It was also observed that the spray produced was greatly affected
by the concentration of the acid, the 60'4/ acid producing a
spray which was coarser and of smaller cone angle than that
from a 40'; acid. The more concentrated acid also required
a greater pressure for the same rate of discharge. It appeared
probable that the final design would have to be a compromise
between the conflicting requirements of the two concentrations
or, alternatively, would have to provide for interchangeable
nozzles for the two acids.
The performance of this model in field tests was a great
improvement over that of the preceding. The spray was much
better and the coverage of the streak and the important bark
overhang reasonably satisfactory. The location of the nozzle
at the end of an extended and upwardly inclined arm per-
mitted better positioning and control of the spray. The chief
criticisms were that the rate of acid discharge was too low and
the air pressure too great, in spite of the fact that the former
had been increased 50'1, and the latter reduced 30'; over the
preceding model. Both of these deficiencies increased as the
liquid level in the acid container was lowered and the acid lift
correspondingly increased. It was also felt that a safety device
should be incorporated in the gun to protect the operator from
a possible reversed flow through the mouthpiece.
The third model (see Fig. 5) was designed to correct the
deficiencies and provide the improvements indicated by the
test of the second. In it the nozzle was lowered nearly to the
liquid level, reducing the acid lift to practically zero. The up-
ward inclination of the nozzle was greatly increased so that, as
the acid was consumed and its level lowered, the container and
nozzle could be inclined downward, maintaining the desired zero
lift feature and at the same time retaining the upward direction
of the spray. Lowering the nozzle in this fashion also reduced
the air pressure required. A non-return valve was provided
in the air supply line to prevent reversed flow to the operator's
mouth. The exterior of the nozzle was altered to protect the
orifices from damage by impact or obstruction by gum. A
drip ledge was provided for the purpose of ridding the nozzle
of the occasional terminal drop of acid left after a discharge.
Both acid and air orifices were increased in area, the former
Nozzle lowered to reduce acid "lift" and required air pressure. Acid
orifice member made self-centering and positioning, and easily removable
for cleaning. Non-return valve provided to protect operator from counter-
flow of acid vapor or liquid. Nozzle tip redesigned to provide protection
to the orifices.
to provide the higher discharge rate desired and the latter to
compensate for the reduced air pressure now required and still
maintain the air flow at the former rate. The design of the
acid orifice member was completely revised in order to obtain
automatic precision positioning of the orifices and to permit
ready removal of the member for cleaning. Experience with
the earlier models had indicated that the small acid orifice was
easily obstructed and required frequent cleaning if foreign mat-
ter was present in the acid charge.
The spray produced by this gun, after the usual test and
modification procedure required by any change in the sensitive
nozzle, was considered to be satisfactory, conforming in every
respect to the then latest specifications of the Southern Forest
Experiment Station. The cone angle was small, about 300; the
droplets fairly uniform in size and rather coarse; the rate of
discharge 1 cc. per 5 seconds at air pressures of 4 to 7 inches
of water over the normal range of operating conditions. (Four
inches pressure was required with 40'A acid and a full container;
seven inches with 60% acid and a half-emptied container or a
nearly empty one inclined to an equivalent degree.) (A com-
parison of these pressures with the approximately eight inches
suction required for soft drink sipperss" will indicate the very
moderate air pressures now required.) The spray was some-
what wider and finer with 40% acid than desired, and somewhat
narrower and coarser with 60%, but not sufficiently so to necessi-
tate interchangeable nozzles for the two acids.
The non-return valve, however, in the laboratory tests proved
unsatisfactory. It was effective against the return of air and
entrained acid vapors but not entirely so against liquid acid
when the gun was inverted and the container air connection
submerged. It was made of the lightest possible construction,
but so low a pressure was now required that any obstruction
in the air passage was immediately apparent. Further, this
disability would be increased if the design were made heavier
in order to provide a completely effective safeguard against the
return of liquid acid. The excellent operation of the gun above
mentioned was obtained with the non-return valve removed;
with it in place the quality of the spray was impaired.
It appeared questionable, however, whether the valve was
needed at all. Oral suction applied to the mouthpiece in the
laboratory investigation resulted in not the slightest ill effect.
It was, in fact, found to be possible to breathe through the tube
and gun. Air bubbled violently through the acid in the con-
tainer, but left the acid safely behind. No detectible quantity
reached the mouth.
This experiment was conducted with the gun in the normal
position. In the inverted position acid would have been de-
livered to the mouth. It may be considered, however, improb-
able that, in service, the gun would be inverted and suction
simultaneously applied to the mouthpiece.
After careful field trial and thorough consideration of all
the factors involved, the Southern Forest Experiment Station
concurred with this conclusion. The non-return valve was ac-
cordingly deleted from the assembly. The field tests of this
model confirmed the laboratory tests. The performance of the
gun was considered satisfactory. No essential changes were
suggested. At the conclusion of the tests, the Southern Forest
people asked to have the model left with them for their own
daily use, and to have four others made for trial by interested
naval stores producers.
This was done, and the five guns were used extensively dur-
ing the remainder of the 1944 season under conditions approxi-
mating those of actual commercial service. No serious troubles
developed, except that the acid orifice members, when made of
plastic, were short lived. Stainless steel replacements were not
entirely satisfactory, as they were subject to corrosion if not
cleaned of acid at the end of each period of use. No perfect
material for this part has yet been found, but a contemporary
investigation of corrosion inhibitors at the University indicates
that a solution of the difficulty may be found along these lines.
Further development of the gun was suspended at this point,
as it was considered that the primary objective of suitable
design had been realized. It had been intended to rteesign
the final accepted model for construction by molding instead
of machining processes in order to improve its appearance and
to expedite production, but preliminary inquiry among manu-
facturers indicated that molding was not practical under the
abnormal wartime conditions then prevailing. Further, a local
manufacturer able and willing to construct the gun to the present
design had been found. Only a few modifications were, there-
fore, made (See Fig. 6.) A sloping sided flask was substituted
for the straight sided one in order to improve the ease of
handling the gun, the air valve and its mounting were replaced
by a simple rubber stopper, the nozzle drip ledge was eliminated
as ineffective and rather unnecessary, and the nozzle slightly
modified to permit easier assembling. The basic dimensions of
the nozzle were not changed.
Straight sided flask replaced with sloping. Non-return valve eliminated
as unnecessary. Seating of acid orifice member improved. Drip ledge
eliminated from nozzle. (U. S. Patent No. 2394424.)
A contract for the production of 500 guns was placed in
1944. The usual difficulties attendant upon any new manufac-
turing program were encountered, aggravated by the abnormal
war situation, and in consequence delivery of the first guns was
delayed for several weeks after the start of the 1945 season.
Total sales for the season did not reach the 500 or more orig-
inally contemplated. The performance of these guns in service
was considered satisfactory, indicating that the design was
TECHNICAL TEST DATA
At the conclusion of the 1944 season, one of the five third
model guns was brought back to the University, reworked to
the form of Fig. 6 (using the sample sloping sided flask sub-
TEST SET UP FOR ACID ORIFICE MEMBER
Data obtained were the time of discharge of successive increments of acid
at constantly decreasing head.
mitted by the sub-contractor for the flasks), and tested quantita-
tively. The tests were made in order to obtain data on the flow
of acid through small bore orifices and on the character of the
sprays produced. No authoritative data were obtained on the
spray characteristics (viz., the cone angle, number and size and
distribution of droplets, etc.) as the test set-up was insufficiently
elaborate; but consistent and rather pertinent data were secured
on the discharge characteristics.
The acid orifice member was tested separately. The air
orifice was tested as a component of the entire assembly in a
complete test of the gun as a unit. The test set-ups are shown
in Figs. 7 and 8, and the results obtained are given graphically
in the diagrams of Figs. 9, 10 and 11.
In the test of the acid orifice, the information directly ob-
tained was the total time of discharge of successive quantities
of liquid flowing continuously under a uniformly decreasing
head. (See Fig. 7.) The rate of discharge at any specified
constant head was not directly determined, but is readily com-
puted from these data. Two methods may be employed. In
the first, the total discharge as ordinate is plotted against the
total time as abscissa. (Fig. 9.) The slope of the tangent to
the curve at any specified point is mathematically equal to the
rate of discharge at the head corresponding to the point. The
determination is a graphic procedure, and its accuracy is a
function of the size of the curve as well as the basic data. In
the second method, the mathematical equation fitting the dis-
charge-time curve is obtained, and the first derivative of this
equation taken. This is the equation of the rate of discharge
and may be evaluated numerically at any desired head. The
accuracy is dependent solely upon the accuracy of the basic
equation, and can be brought within any desired limits. Both
methods were employed and served as a check on each other.
The total discharge-total time curves for both 40% and 60%
sulphuric acid are given in Fig. 9, and the rate of discharge
curves are given in Fig. 10.
Also shown in Fig. 10 are the coefficient of discharge of the
two concentrations. The coefficient of discharge is the ratio
of the actual rate of discharge to the ideal rate for a friction-
less orifice. The ideal rate is mathematically computed from
the dimensions of the orifice and the head of the liquid flowing
according to the usual equation Q=A(2gh)l '. In this equation,
TEST SET UP FOR SPRAY GUN
Data obtained were volume of air supply and rate of acid discharge at successive acid levels during discharge of entire
container contents. Tests were conducted over a wide range of air pressures.
o9 Xs 504 ;
60%/,/ S ;
of D.L/5cc Curvej
oI A f7/" Y0- eaoee "-a
where ca. cef/Cmterrs
oa a.tf "eAe/o D/r/9es-
a ozwws~w" /AS4 ao, '
C44wFr7Z'7Y OfCEf'/?Vf/ HfAf
*C-ro fA L0 r- I APl^ I
DISCHARGE-TIME CURVES OF ACID ORIFICE MEMBER
Acid was discharged through the orifice from a graduated burrette, the acid liquid level falling continuously and
decreasing the head on the orifice and increasing the time required for the discharge of successive quantities of acid.
From the slope of these curves, or from the equations of the curves, the rate of discharge at any head can be determined.
Q is the rate of discharge in cu. ft. per sec., A is the cross-
sectional area of the orifice in sq. ft., g is the acceleration due
to gravity (approximately 32.2 ft. per sec.), and h is the head
in feet of the liquid flowing. For a rate of discharge expressed
in cc. per min, and a head expressed in inches, this equation,
for an orifice of 0.025" diameter, reduces to
c12(100) 1c 1f2(100) 7r(0.025)= 2(32.2)hl'i
cc/min 60 Q 60
39.37 I 39.37 4(144) 1 12
RATE OF DISCHARGE CURVES
(derived from Fig. 9), and Coefficient of Discharge. Note that the head
of the graph is the head of the liquid flowing, viz. 40% or 60% H.SO..
To obtain the equivalent head in inches of water, multiply by 1.3 for 40%
H,SO, and by 1.5 for 60% H,SO,. Because of the high viscosity of H,SO,,
the flow is retarded at low heads and ceases abruptly at a little less than
1" head. For this reason, heads less than 3" of H,SO., or 4-5" of water,
are inefficient, as shown by the curves of Coeficient of Discharge.
The numerical value of the coefficient of discharge for orifices
is usually well above 0.90 for water. The values in this case
were much lower, particularly at very low heads. This may be
attributed to the capillarity of the orifice and to the high vis-
cosity of the acid.
ACID DISCHARGE AND AIR REQUIREMENTS
of "Florida" Acid Spray Gun, design of Sept. 4, 1944, when discharging
40'/t HSO,. As an example of reading, it may be noted that with 5" water
pressure applied to the container and a lift of 1" from container liquid
surface to nozzle tip, the gun will discharge 12 cc. of acid per minute and
requires 230 cu. in. of air per minute, equivalent to 1 cc. of acid and 19 cu.
in. of air per five seconds. To obtain the same acid discharge rate at 3"
lift would require, from the curves, 8" of water pressure and 285 cu. in.
of air per minute. These curves, together with those of Fig. 10, may also
be used to predict the effect of design modifications and the use of other
acids. For example, to deliver 12 cc. per minute of 60% H2SO. at 1" lift
3.3 x 1.5
would require (from Fig. 10) 2.8 x 1.3 or 1.36 times the 5" of water re-
quired for 40';1 H SO., or 6.8" of water pressure. The air flow correspond-
ing is 270 cu. in. per minute.
In the tests of the complete nozzle and gun, the gun was
discharged from full to empty by air at a constant predetermined
pressure from an air compressor. The total air consumption
was metered by a precision gasometer. As the falling liquid
level passed elevations corresponding to 0, 1, 2 and 3 inches
liquid lifts, a small quantity of spray was intercepted and
measured and the time of discharge taken. (See Fig. 8.) A
number of tests were run at air pressures of 4 to 14 inches of
water, and yielded data from which the calibration of the air
orifice could be obtained over this range of pressures. The
data of acid discharge plotted directly into a series of curves
(see Fig. 11) of rate-of-discharge-at-constant-liquid-lift as a
function of air pressure. It also permitted a series of derived
curves of rate-of-discharge-at-variable-lift-but-constant-effective-
orifice-pressure versus air pressure.
The rate of acid discharge at zero lift in the complete gun
assembly was slightly less than the rate in the test of the acid
orifice alone. This indicates that, in this particular nozzle de-
sign, the flow of air at the nozzle mouth has no suction effect
on the liquid orifice. Further, as may be seen from the down-
ward slope of the constant-orifice-head curves, an increasing
air flow is accompanied by a reduced liquid flow, showing quite
the reverse of a suction effect. This is contrary to the opinion
entertained before the tests were made. The air flow was ap-
parently similarly affected by the acid flow, but the variations
were too small to be correlated to the flow conditions.
The rates of discharge and pressures established by these
tests of the final design may be compared with the original
specifications or assumptions for the first model. Over the
normal range of service operational conditions, the air consump-
tion and pressure of the final design were only half, and the
acid discharge double, the original estimates.
PERFORMANCE OF THE FLORIDA SPRAY
GUNS DURING THE 1945 SEASON
The appearance of this acid spray gun in the summer of 1945
may prove to be an event of considerable importance in the
naval stores industry. Until that time it had been impossible
to apply the principles of chemical stimulation to large-scale
CHIPPING A STREAK ON SLASH PINE
using the special hack developed by the Southern Forest Experiment
Station for "bark chipping." Note the Florida Spray Gun affixed to the
tree by means of a homemade hanger.
The spray gun was immediately placed in service under a
wide variety of operating conditions. The work areas varied
from those in open grown timber with little or no ground cover,
to dense growths of woody shrubs and vines. The faces treated
varied from those close to the ground on trees worked for the
first time, to those much higher up the tree after several years
of work. The type of streak was both the conventional one-
SPRAYING THE FRESHLY CUT STREAK
Note that the upward slope of the spray permits coverage of hark
overhang as well as the face of the streak, and also that one hand only
is required in the operation of the gun.
half inch in height and depth into the wood and the newer
more shallow chipping in which only the bark is removed down
to the wood. (See Fig. 12.) The gun was used by small colored
boys who followed and were supervised by the chipper and by
more skilled and experienced workers who both chipped and
Under all these conditions the spray gun performed in an
outstanding manner. Its design permitted its adaption to the
wide variety of conditions and its simple operation was easily
mastered by the most unskilled of woods labor. (See Figs.
12 and 13.)
The operational efficiency of the spray gun was so high that
small boys were able satisfactorily to apply the treatment fol-
lowing the fastest chippers. The energy necessary for its
operation was conspicuously less than that required by the
better of the hand pump models.
The material used in the construction of the gun was suit-
able for the purpose. As stated in Section I the metal orifice
member, while made from stainless steel, was not acid-proof.
It was, however, quite acid-resistant and changes in size due
to corrosion were slow. Replacement was possible when the
spray characteristics began to vary from the normal and, owing
to the simple design, this required only a few seconds and could
be done in the field without tools.
HISTORY OF THE DEVELOPMENT OF CHEMICAL
Shortly after World War 1, Germany and Russia initiated
intensive programs to improve and expand their naval stores
industries. It was during this initial period of expansion, when
these countries were attempting to become self-sufficient in all
important raw materials, that the use of chemicals to stimulate
gum yields first received attention.
Research workers in Germany initiated studies in the use
of chemicals to stimulate gum about twenty-seven years ago,
and somewhat similar work was started in Russia also at about
the same time. In these early exploratory experiments many
different types of chemicals were used as liquids, solids, or
gases. These included acids (organic and inorganic), bases,
pure salts, various solvents, oxidizing and reducing agents,
poisons, and relatively inert substances like alcohol, sugars,
ether, and oils.
Many of the substances tested exhibited a stimulating action
on the flow of gum. A few, such as sulphuric and hydrochloric
acids, and sodium and potassium hydroxides, were outstanding.
Much of the subsequent work has been with these chemicals.
The small attention given the other chemicals does not preclude
their potential value in stimulation, but indicates simply that
in the concentrations tested, and under the experimental condi-
tions prevailing, they did not cause as much increase in gum
flow as the two acids and bases mentioned.
Numerous different techniques, as well as chemicals, were
tried in the early European work. These included methods of
applying chemicals, variations in chipping heights and depths,
and different frequencies of treatment and chipping.
In this country the first work on chemical stimulation was
started in 1936 as a cooperative study by the Southern Forest
Experiment Station, U. S. Forest Service, at its Olustee Experi-
mental Forest, Lake City, Fla., and the Bureau of Agricultural
and Industrial Chemistry, (formerly the Bureau of Chemistry
and Soils). Results of this early exploratory study were in-
conclusive. At that time there was a surplus of turpentine and
rosin, prices were low, and there was little interest in chemical
stimulation, but in 1938 a larger experiment was started to
explore the possibilities further.
The promising increases in yield obtained in the 1938 ex-
periment, even at the low concentrations in which the stimulants
were used, gave further impetus to research, and additional
work on yield capacities of individual trees was done in 1940.
These yield records served as the basis for dividing the trees
into yield-capacity groups which were almost identical. Then
in the 1941 seasons one group of trees was worked untreated, and
the others assigned treatments which covered a wide concen-
tration range of sulphuric and hydrochloric acids, the two chemi-
cals giving best results in the former experiments. The results
of this study formed an important link in the chain of evidence
upon which recommendations to industry were made in 1942
Shortly after our entry into World War II an intensified
research program on the use of chemical stimulants was in-
stituted. This covered the use of many different chemicals in
varying concentrations, numerous variations in chipping and
treatment schedules, variations in height, depth, and frequency
of chipping, studies on species differences, and the effect of
chemicals on gum quality and the health and vigor of the trees.
These studies established optimum techniques for correlating
chemical stimulation in naval stores practices to increase gum
yields and efficiency of operations.
In connection with the studies of the effect of various chemi-
cals on the total yield of gum, data were also secured on the
diurnal, weekly, and monthly rate of the flow of gum from
treated streaks. The curves of gum flow for the various time
periods following chipping and treating focus attention on the
way in which the principles of the treatment may be best utilized
to secure certain objectives under a variety of operating condi-
tions. One of the type curves showing the yield of gum from
one treated streak and three untreated streaks over a three-
week period is shown in Fig. 14.
The curve of gum yield from the treated streak shows that
for the first week gum flow was rapid and was greater than
that from the untreated streak. It also shows that gum was
produced during the second and third weeks but that by the
end of the third week the flow had practically ceased. It also
shows that at the end of the third week following chipping and
treating, the total amount of gum produced by the streak was
equal to that produced by the three untreated streaks.
3 THREAT UNTREATED
ECONOMICS OF CHEMICAL STIMULATION
Yield of gum over a three weeks' period from (continuous curve) one
streak treated with sulphuric acid spray and (broken curve) three un-
treated streaks made at one week intervals. The total yield from the
one treated streak is equal to the yield of the three untreated streaks
and is obtained at substantially reduced cost to the producer.
The curve of gum yield for the three untreated streaks show
that while the yields were high for the first two days following
chipping, the flow had practically ceased by the end of the week.
To secure additional gum it was then necessary to apply an-
Two principles are clearly illustrated. The first is that in
a period of one week the flow of gum from a treated streak
is significantly greater than that from an untreated streak. The
second is that an acid treated streak continues to produce gum
for a three-week period and that the total yield is equal to that
of three untreated streaks.
How may these principles be applied by a naval stores pro-
The first principle of increased weekly yields makes it pos-
sible, with additional labor to apply the chemical to weekly
streaks, to increase the total gum yield for the season. The
experimental data show (and they are supported by the results
from commercial operations) that this increase may be about
60% of the normal production of average producing timber.
As only about one-third of the value of this increase is required
to pay the cost of treatment-labor, chemicals, and application
equipment-the remaining two-thirds is additional net profit over
that which would have ben secured from the timber worked
with the usual methods.
The second principle of prolonged gum flow from a treated
streak is applicable as a means of increasing the chipper's
efficiency and conserving the workable portion of the tree. Both
of these are extremely important.
Under present methods of naval stores production an aver-
age 10,000 tree crop will produce 200 barrels of crude gum from
32 standard streaks during the period from about March 15th
to November 15th. The production per streak per 10,000 trees
is then 6.3 barrels of gum. If 11 acid-treated streaks are ap-
plied at intervals of three weeks during the same period and on
the same type of timber the same volume of gum will be secured.
This is a total production of 200 barrels of gum from 11 streaks
or 18.2 barrels per streak. The yield per streak is 2.9 times
that of an untreated streak.
The increased efficiency of production with the lowering
of production costs is clearly apparent. Acid treatment requires
some additional time and reduces the usual number of trees
a chipper can work by about 20%. However, one chipper can
cover a different area each week and over a three-week period
produce much more than with the standard method of working.
If his uIsual chipping production per week is 5,000 trees, with
the additional work of acid treatment he is able to chip and
treat only 4,000 trees. He can, however, cover a different area
each week of the three-week period and thus secure the pro-
duction of a total of 12,000 trees, which is 2.4 times as much
as he could produce without acid treatment.
The amount of work time required Lo apply the acid is an
important factor in this type of work. If the acid treatment
required a negligible amount of time so that he could still cover
5.000 trees each week. he could cover three such areas, and the
amount of gum produced each season would be three times that
previously possible. It is hoped that the development of a com-
bination spray gun and chipping hack will make this possible.
With such a tool operating under higher pressures and requir-
ing no additional equipment to be carried and requiring no loss
of time for refilling, the chipping and treating operation should
be highly efficient.
Another valuable application of the second principle of pro-
longed gum flow is in the conservation of the workable portion
of the tree. The amount of wood or bark removed for each
streak, either if treated or untreated, is about one-half inch
in height. If a treated streak, running for a three-week period,
produces as much as three untreated streaks, each one-half inch
of face length is three times as efficient. With acid treatment
it is therefore possible to secure as much gum as is now secured
and use only one-third as much of the tree. Under the usual
methods of working timber for naval stores, approximately 20
percent of the total merchantable volume is made valueless for
other products by the scarring and the nails used for attaching
the gum collecting equipment. If this waste is reduced by two-
thirds the tree has a significantly increased salvage value after
the chipping operation is completed.
In the relatively short time that methods of stimulating gum
flow with chemicals has been studied, much has been accom-
plished. The basic principles of both increased and prolonged
flow have been established and both have been accepted, used,
and proven on large-scale commercial operations.
The gum naval stores industry is extremely sensitive to the
competition offered by the wood naval stores and petroleum in-
dustries. To hold its place with these well-established com-
petitors it is essential that its products be produced at as low
a cost as possible. The use of chemical stimulants is one very
important way in which this may be accomplished.
FIG. 15.-EARLY DEVICES FOR ACID APPLICATION
A. Open container and swan. Brushes were also used. II. Insecticide spray gun. C. Nasal atomizn.er. I). Nasal
atomizer in carrying case. IE (Commnercial spray gun. F. Same gunl as E, but miodilied with special nozzle and larger
container. G. >iqueeget Acid is.releasied when fll ibl i4, ile is wied over.trlnk. .
RESUME OF OTHER DEVICES USED FOR ACID
Throughout the experimental work and the development of
commercial practices in the use of chemical stimulants, many
different methods of applying the solution have been used. Two
general types of equipment which were both cheap and available
received the most widespread usage. These were brushes or
swabs and small spray guns and atomizers.
The most simple earliest tools were cloth swabs and paint
brushes. The swabs were prepared by the operator by wrap-
ping and fastening cloth securely around the end of a short
stick. (Fig. 15-A.) The chemical solution was carried in an
open container such as a small fruit jar. The swab was dipped
into the solution then brushed along the streak. The advantages
of this method were that it was inexpensive and would give
satisfactory results if used by a competent worker. The dis-
advantages were that an extra man was usually required to
do the treating as it was fairly slow and required the use of
both hands. It was also difficult to regulate the amount of solu-
tion that had been applied. Cloth is not acid resistant and soon
wears away, causing a progressive decrease in the amount of
solution it will absorb. With the stronger solutions, such as
60%7 sulphuric acid, it was necessary to use cloth made from
glass which was not readily available. There was also the
possibility of getting the solution on the clothes of the operator
either from the open topped container or the swab.
Small paint brushes were substituted for the cloth swabs
in some instances. They showed no appreciable advantages
over the swabs.
An instrument similar to the swab and brush but more
efficient and safe was developed for use in the experimental
work. This applicator is shown in use in Fig. 15-G. The in-
strument consists of a glass laboratory aspirator bottle with an
outlet near the bottom to which is affixed a short plastic tube
with a rubber nipple. In operation the nipple is moved along
the streak with slight pressure against the surface. This pres-
sure opens the hole in the nipple, allowing the acid to flow onto
the surface of the streak where it is spread somewhat by the flat
end of the nipple. This instrument was much safer and easier to
use than swabs but applied acid to only one surface of the streak.
With chipping to bark depth only it is necessary to apply acid
to both the upper and the back parts of the streak to secure
the maximum results.
As the experimental work continued it became increasingly
evident that more efficient and practical methods of applying
the solution were needed. Spraying seemed to be necessary to
secure an adequate amount in the correct place. Means of ap-
plying the solution as a spray, however, were not plentiful. For
small-scale work it was found that some commercial models of
nasal atomizers could be used. (Fig. 15-C and D.) These were
equipped with a rubber bulb for applying pressure, a glass
container, and nozzle assembly parts of hard rubber. All these
materials were acid resistant. They were designed, however,
to atomize rather than spray and also to discharge at a much
lower rate than necessary for rapid work. They could be im-
proved somewhat by increasing the nozzle opening and using
a larger container. The small size of the parts required fre-
quent adjustment to keep the desired spray characteristics, and
in addition they clogged frequently. As with most spraying
equipment, two hands were required for operation.
Another type of spray gun used on a limited scale by com-
mercial operators were those designed to spray insecticides.
(Fig. 15-B.) These small metal guns were inexpensive, which
made their use feasible even though they would withstand the
strong solutions for only a short time. Their spray character-
istics were not entirely satisfactory in that they were designed
to atomize rather than spray.
One hand spray gun which was already in production but
which had been designed to withstand less corrosive solutions
than were used in this service (Fig. 15-E), was modified and
a number were used throughout the industry. The nozzle was
changed and the solution container was enlarged. (Fig. 15-F.)
Although the materials used in construction of the gun were
made of more acid resistant materials it was not possible to
improve them to a point where the performance was satisfactory.
Wartime manufacturing conditions made the development or
modification of any equipment extremely difficult. This spray
gun, like the others, required the use of both hands to operate,
and contained valves and pump parts which were subject to
corrosion from the acid as well as mechanical wear.