The flotation method of determining the specific gravity of wood

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Title:
The flotation method of determining the specific gravity of wood
Physical Description:
Book
Creator:
Paul, Benson H
Forest Products Laboratory (U.S.)
University of Wisconsin
Publisher:
Dept. of Agriculture, Forest Service, Forest Products Laboratory ( Madison, Wis )
Publication Date:

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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 29314229
oclc - 755795618
System ID:
AA00020574:00001

Full Text
Till FLOTATION MAITlICI 01 I)ITIEPAININC
TEEl SIPECIIIC GCPAVITY Of WOCl)
Revised July 194C3
UNWESIFYOf fiRk;0
This VPeport Is One of a Series'
Issued In Cooperation with the
ARKMY-NAVY-CI VII. commilrE
on3
AI]CR~Aff VIEIGN CIRITI1A
Under the Supervision of the
AMONAUTI CAL 13MA I)I
No. 13%8
UNITED STATES DEPARTMENT OF AGRICULTURE
I FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison, Wisconsin -
In Cooperation with the University of Wisconsin







THLE FLOTATION ;,.ETHOD OF DETF i.INI1TG THE
SPECIFIC GRAVITY OF ,:fo od;:
BY
BENSON H. PAUL,
Senior Silviculturist
A method of estimating the specific gravity of wood quickly and to a reason-
ably accurate degree with a minimum of time and equipment has beer, developed
at the Forest Products Laboratory to assist suppliers of lumber used in war
production in meeting specification requirements for weight. Wh ile thl-e
method may: not be so accurate as the standard process described in --rmy-17a,%y
Specification AYT-W -4a, its time and labor saving features should mak_-e it
useful for producers seeking a quick specific gravityz test to guard a-,ainst
the use of underweight material and, at the same time, avoid the rejection
of wood of acceptable specific gravity. The method is believed accurate
enough to detect up to 90 percent of stock which should be rejectabie for
light weight. Use of the more accurate -,-Iethod outlined in Specification
AN-W-4a is, of course, recognized as necessary in making final assessment of
the quality of wood in such border-line cases as may arise from t-ime to ti-.e.
Essentially, the method consists of determining the proportion of a piece of
wood with parallel sides that is submerged when it is floated in water. To
facilitate this determination, the method calls for a test specimen 1 inrch
square in cross section and 10 inches long, marked into 10 equal divisions
of 1 inch. When a piece so marked is floated upright in a cylinder of -.rater
(fig. 1) its specific gravity at current moisture content car, be ascertained
by observing the proportion of the piece that is submerged.
For example, if six divisions of the piece are under water, the specific,
gravity is 0.60, while if it sinks to the seventh mark, the specific gravity
is 0.70. 1hen. the water level reaches a point somewhere between twro divid-
ing m,,,rks on the piece, specific gravity may be visu.-all-r estimuat d ,ith
reasonable accuracy; a water. level half wayr between 6 and 7, for ex !7-ple,.
may be road as 0.65. 0t'herl"L-e~diate levels may be rather closely estiza ted
as 0. 52, 0. 67, and so on.
Any container, of suitable size to hold the specimen vertically or nearly so
and yet allow the specimen to float freely may be used (fig. 1). If thec
container is filled with water so that it will overflow, the specimen can be
Quickly marked at the water level before absorption of water takes place.
1This is one of a series of progress reports prepared by the Forest Products
Laboratory relating to the use of wood in aircraft, Results here reported
are preliminary and may be revised as additional data become available.

Report iNo. 1398




Tests of :nany sales of equal length can be speedied br use of a scale of the
sa ie len-tr-_ *airk in 10 equtlal units. The proportion s-_-.1-eredd is read by
p~hin the speci:.en beside t.e scale. For rpii sorting, the reU4red
ii..er;ion depth mny be ...arked on specimens before test.
For comparison %ith standard specific gravity value-s, specimens rf-hould be as
noarl,. 7 misture free as possible unless the moisture content is --no-n ad. tLhe
roriete Lorrection made. The method is not applcable to green wood.
Scc..enf for test may be cross cut fro- the ends of boards. If it is not
cornv2Lient to ct specimens 1 by 1 by 10 i_--chcs in size, another size n be
cIosen -- a ienbtli of 5 inches, Derhaps, with a uniform cross section. W1e re
possible, s ecfi-is should be dried before test to an oen-dr, condition.
When it is desirable to determine the specific gravity of specimens of vari-
ous lengths (but, of course, with parallel, sides) t:ne spccimn is floated and
the water level marked. The i.. ersed Lngth is ;.easurcd, ad- t'-is value,
w;_ien divided by the total lengt- of t,,e spcciuen, Cives its specific gravity.
,hn testing sam-oles that are not oven dry, buat for which the current :ois-
ture consent is known, a formula developed at the Foresz- Products daorlotory
nay b. used to ;:ake a simple correction calculation fro_ current volume ad
moisture content to oven-dry eigt and vol. in this fora a correction
factor, K, is employed as a constant for each cr.n;e of 1 percent in noiatre
content for a given species. This factor coriensatcs for shrinkage also.
For a sal.iple tested at II percent moisture content, the formula is:
Specific gravity equals current specific ravity at X moisture content
minus KCX.
Assu-in,, a moisture content of 15 percent for a spruce specimen, and a
current specific gravity reading by the flotation method of 0.42, the formUla
may be used as follows:
First from the accompaninz tabl, obtain the correction factor, (0.00133)
for spruce. Substituting the value in the formula, the following equation
is o1--t,.ined:
Spc~cific gravity equals 0.42 minus (0.00193 times 15)
By simple arithmetici the approximately specific gravity of the specimen at
ovcn-1dry weigC't and volume is found to be 0.39.
The values in the last two columns of the table have. been computed to adjust
the current specific Cravity (grams per cubic centimeter, col. 11) and
pounds per cubic foot (col. 12) for erch 1 percent chae in moisture content
of aircraft woods.
2 2-4 in lC*3 editiori of !"od Aircraft Inspection and Fabrication inua

report 1o. l391,9

-3-




-111 ~

L

Table 1 -Measn and sntamm values of esecino gravity and wesht for various arafE1t
Woode under different conditions of moisture and secommnrina adIating constant
-OISpecif gravity ad weight per oube foot- Grane pe onbio centimeter and pounds per cubio foot Constantal for adjusting values for
apific gravity: seed on weight and volume when oven try 'basd on weight and volume at 10 percent moisture content eoh I percent Change in solsture content
bad on -:-------------------------------------------- ---
species I weight when I Average Minimum persitted : Avrae: Minim pemitted
oven dry and I- -----------------------------------...------.---.-.- --------------------------- For grea per for pounds per
volume when :spectif'l ight perSpecithg :Ueight per -Gea ar oubic'ght par :Greas pertoubio: Weight per cubic centimetera c bic food
a green I gravity oubi footgravityAk :oubi foot : centimet A :oubic food: contimeterm,: oubic foot& :
----- -------------- - --- ------i-------- --------------- .. ... ... .,- ---- --------- ------ ----:---- ------- -- --------- ------- ---------I
(1) a (2) a (5) a (4) 1 (6) 1 (s) (7) a (8) 1 (*) 1 (10) (11) 1 (12)
------------- ------------------ -----------------:----- -------- :----------- ----------------------- -------------------------- ---- --------------------- -------------------
: Pend s : Eounds I :
Maravoods (brosalaved spooin) :
Ash, black ..... .. 0.461 0.531 1 35.1 0.48 30.0 0.63 34.6 1 0.502 31. 0.00147 0.092
Ash, comeroa it .....::::::: .@SS : .618 1 38.6 .66 34.9 : 6ebl t 40.6 b .693 : 37.0 a .00220 & .137
assood, Ameron ...........: .Usb 1 .39e : 24.8 .36 28.6 .406 26..3 .367 22.9 .00047 .029
Beech, American ..............: .063 .671 : 41.9 .60 1 37.4 8 .694 4. 1 .623 38.9 .00160 .096
Biroh, Aska ................t .488 .694 1 39.1 1 .63 : 3.1 : .07 1 37.9 1 .543 I 30.9 & .00087 .054
Biro, paper ................. 48400 : 57.4 : 64 : 3 .407 537.9 3 .647 : 100049 .029
Biroh, aweet and ye:llo ......: .074 .08 a 42.9 1 .68 1 36.2 1 .709 44 .601 376 8 .00140 & .087
Cherry, black ................t .471 .634 3. : .48 3 0.0 .669 315.6 .1 bl 32.1 1 .0085 .14b
Cottonwood, eastern .......... .372 : .433 : 87.0 .39 24. : .464 28.3 1 .411 5 26.6 1 .00140 .087
S1, Amerioan ................: .458 .654 t 34.6 5 .50 a 31.2 1 .668 36.4 1 .514 32.1 t .0009a a .058
Ma, rook ..,.......o .....: 674 .668 41.1 3 .60 a 37.4 : .696 : 43.4 : .638 : 39.8 3 .00865 : .158
Stokory (true hIckeoriesP....: :641 1 .001 : 00.0 .71 44.5 1 ,806 60.3 4 .716 S 44,6 5 .0003: .021
Ebays ('African mahogany) ...: .429 5 .467 1 29.1 .42 : 6.2 : .510 31.8 1 .463 28.9 I .00289 in19
Locust, black ................: .669 i .708 t 44.2 .64 : 9.9 .779 48.6 .711 : .4 .00473 .295
nolis. southern .........: .460 : .030 : 35. 1 .48 1 30.0 : .69 34.9 : .509 : 1.8 : .00193 .120
any ........... .469 .08 : 51.7 .46 t S8.7 .649 : 4.3 4 .51 31.5 .00273 .170
Maple, red ................... .486 1 .646 8 34,1 .46 1 28.7 .685 36.b t .499 31.1 : .00260 .162
Maple, silver ..............: .49 : .06 : 3.6 .46 28.7 .634 33. .488 50.6 t .00167 .11l
Maple, sugar ...... ........: .664 .676 42.2 .60 : 37.4 1 .697 43.6 3 .621 38.8 t .00140 .087
Oak, cammerol .61 .676 42.2 .62 : 38.7 .696 4.4 : .659 59.9 .00127 .07S
Oak, ercial whit* ....::: : .692 ,719 3 4.9 .62 58.7 : .936 45.9 .657 39.7 z .00113 .071
Peon ......................i .601 .694 : 43.3 : 62 58.7 .751 : 46.6 .657 41.0 .00247 .164
Seegu ..................... .441 3 .530 : 53.1 : .48 : 30.0 t .646 : 4.1 : .496 : 31.0 1 .00107 .067
Syeasore, American ...........: .456 .559 : 3.6 .49 : 0.6 .060 34.9 .511 31.9 .00140 .0e7
Topelo, water ............... :. .64 : 32.7 .49 29. : .Se3 34.5 .499 : 1.1 .00193 .120
Walnut, black ................: bl3 62 : 36.1 .62 32.4 .611 : 38,1 .669 55.6 1 .00587 : ,4
telloupoplar ................: .376 .427 : 26.6 .38 25.7 .464 : 28.3 .407 26.4 .00180 .112
softwoods (conirrous Sooes)
Baldoyprese ..................: .426 .482 1 30.1 .43 26.8 .613 52.0 .41 28.8 .00207 .129
Cedar, Alaska ................ .415 .466 1 29.0 .41 26.6 .499 31.1 & .444 : 27.7 : .0227 .142
Do la-fir (oast) : 3
1 ................: .448 b 612 31.9 46 2.1 .645 : 30,9 .401 : 00 .00907 .129
Class L .................: .581 : .452 : 27.0 :11.38 : .7 .460 : ee. : .408 : 126,6 .00187 .117
Fir, California red ..........: .372 .421 : 26.3 : .38 : 83.7 .449 28.0 .408 & 26.5 .00187 .117
Fir, noble .................... .351 .403 : 86.1 .36 : 28.6 .426 26.6 : .385 Z 83. : .00167k .095
Fir, Pacific silver ..,, ...: .361 .415 5 26.9 .38 23.7 .431 2 86.9 .86 24.7 .00107 .067
Fir, sbite .............,.... .348 ,397 ; 24.6 1 .36 22.6 .421 26, : .384 24.0 .00160 .100
Belook, western .............: .382 : .448 ; 7.6 t .40 : 6.0 .466 29.1 5 .425 : 126.4 .00165 ,096
Incense-edar, California ...,: .346 .36 : 2,8 .32 20.0 : .406 : 2h.3 .361 : 22.b .00975 .170
Larch, western ............... .482 ,687 : 36.6 .63 33.1 : : it. .645 : 3.9 .00087 .054
Pine, eastern white .........: .344 : .373 ; 23.3 .34 z 21.2 : .408 26.6 .576 23.4 : .0025U .146
Pine, pondereS .............7 : .379 .490 26.8 .38 25.7 : .464 : 81 : .44 26.8 .00227 .142
Pine, red ...................* 440 : .09 31.6 : .6 28.7 .666 : 3.4 .488 : 30.6 00187 *11'
Pine, sugar .................. .348 .398 23.6 .34 21.2 .410 26. .576 : 23.4 .00= .146
Pine, vestern wbite .......... .363 .418 26.1 .B : 2.7 : .441 : 270 : .403 : 26.1 .00160 .096
Redoeder, western ...........: .310 : .42 .31 : 19.3 : .370 : 2. : .3: 21.1 : .00187 117
Redwood ......................: .380 .41 26.0 : .36 25,7 .4b5 28.3 .417 26.0 .00247 *4
Spruce, red, whtse, and Sitka.; .362 .407 : 26.4 .3 22.6 : .4 : 27.2 .389 : 1224.3 .0019Z .120
White-oedar, northern ....... .293 .315 19.7 .S 16.1 .346 21.6 z .321 20.0 .00907 .129
White-cedar, Port Orford .....: .399 .440 : 27.6 :.40 26.0 .477 29,8 .437 & 7.3 .00247 .15*
I(Columns 11 and it.) To adjust value to an oven-dry weight and volume bass or to any desired moisture content, add oontant to value to be adjusted for each I percent increase In
moisture below the fiber-saturation point; subtract constant from value to be adjuesed for eacb 1 percent decrease in molture below the fibor-sturation point. These counsass
take shrinkage or selling witht moisture changes into consideration.
blinimum permitted values are from ARC Handbook on Design of Wood Aircraft Structures Supplement No. 2, page 11, taole 2-1, February 1943.
AlValues in column 7 are obtained by taking 1.15 tise the quantity, Column 5 mins five-eighths of the difference betwan column 3 and Column 2, naeO,
column 7 1,15 od. 3 6/8 ol. 3 col. 2, ; (Col. 7 0cl. 3) 15 = Col. 11.
AValues in this column are equal to values in column 7 t1s 62.4.
Vluan in %his column are equal to value* in column 5 plue column 7 sinus column 3.
alV*use in this column are equal to Values in column 9 times 62,4,
Values in this column are rounded from the product of the values in column 11 and 62.4. These ay be used for direct adjustment of poUnd0 per oubio foot with diffs4rencs in a ture
content below the fiber-saturation point but will be only approximate for Changes greater than 8 percent moisture.
1Enoludes vbite ash, green ash, and blue asb.
I1ooludos shellbar hlokory, sookernet hiokory, pignut hickory, and abagbark hickory.
LQIncludes material from Central Amerion and Cuba.
1Includes white ovA, bur oat, examp chestnut oat, and post oak.
UIoludes northern red oat, southern red oak, laurel oak, water oak, ewamp red oak, willow oak, and black oat.
LAThis value does not agree exactly with the value given in current ANC specifications. The Values In the specifications were prepared under slightly different ba*1c assumptions
and are as follows: Douglae-fir, class N, 29.7, class L, 26.1; western helock, 26.7; Sitha apruce, 23.9.
1%Maximum value permitted, Douglast-fir, lass L, 0.47; Port Orford vbite-oedar. 0.66.
Z N! 46o62 F I




Pigur 1.-Flotation method of determine
specific gravity. The cylinder
should be filled to overflowing
with vater, and the water line
marked on the specimen imdi-
Z V 41631 F ately after immersion.




Ts T
RESTRICTED
CLASSUMM INXIIMZNT




UINIVERSITY OF FLORIDA
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