August 1950 ET-290
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
AN IMPROVED SYRINGE HYDROMETER
By C. V. Bowen,
Division of Insecticide Investigations
The fragility of specific gravity hydrometers is a well-recognized
objection to the use of this apparatus, especially outside the laboratory
or when used by others than chemists or physicists. Any scheme where-
by a hydrometer may be handled with decreased likelihood of breakage
is of value.
The vat-side test, described by Bowen (1), for the toxaphene content
of emulsions used for cattle dipping specifies the use of an API hydrom-
eter in a syringe. In this equipment there is a double possibility of
breakage, because the syringe tubes, as well as the hydrometers obtain-
able from commercial sources, are made of glass. Breakage of either
the syringe tube or the hydrometer may result in inability to perform the
test unless a "spare" is carried in the test kit. The hydrometer must
also be removed from the syringe between use and in transportation to
prevent breakage by the two glass objects jarring against each other.
This procedure requires extra handling of the hydrometer and increases
the possibility of breakage.
The glass hydrometer (fig. 1, D) may be used with much less possi-
bility of breakage if the glass tube of the syringe is replaced with a rigid
transparent plastic tube (C). This plastic tube must be insoluble in or
inert to chemical action by the liquid or solutions to be read. For a
-7-inch API hydrometer with-t float 9/16 inch in diameter, a plastic tube
of 3/32 inch wall thickness, 5/8 inch inside diameter, and 11 inches long
has been used as the syringe tube. About 20 to 25 ml. of liquid is enough
for a gravity reading. A short piece of plastic tubing through the bottom
stopper (F and G) may be used to affix the rubber filling tube.
The syringe apparatus should have two retaining inserts, with open-
ings to allow the passage of the liquid and air, at each end of the syringe
tube--the upper insert (fig. 1, B) to prevent the hydrometer from either
rising into the bulb or falling into the bulb on being inverted, the lower
insert (E) far enough from the end of the tube to permit the insertion of
a stopper(H) if the filling tube is attached in this manner. These two
inserts confine the hydrometer so that it is limited in its longitudinal
motion. If the syringe should be dropped and hit on either end, these
inserts, together with the bottom stopper or bulb, act as a double
cushion to prevent breakage. If the syringe should fall and light on its
side, the bulb (A) and rubber stopper (H) at the lower end would absorb
the shock and the hydrometer in the plastic tube would be protected
against breakage. A soft rubber square or pentagon-shaped collar about
1/4 inch thick placed around the base of the syringe (G) prevents the
apparatus from rolling while lying on its side and acts as an additional
cushion when dropped. A fall in which the side of the plastic syringe
tube makes a direct hit on the edge of a solid object may break the
hydrometer, although such a hydrometer apparatus has fallen in this
manner many times without breakage.
Rubber stopper, inserts, and tubing may be used where the liquids
or solutions to be tested do not attack rubber, but when xylene or other
liquids that do attack rubber are to be read, neoprene or an inert
flexible plastic material should be substituted for the rubber at all
This plastic syringe is the ideal carrying case for the hydrometer
and eliminates the handling of the spindle, which is necessary where the
hydrometer must be removed from the syringe and packed separately.
This type of apparatus also offers less possibility of breakage than types
in which the hydrometer is used to test the gravity of the liquid in an
Although this apparatus was devised for use in assaying the toxaphene
content of cattle-dip emulsions, by the selection of the hydrometer, this
improved syringe-type hydrometer may be adapted to wide usage, such
as the testing of batteries and radiators.
(1) Bowen, C. V.
1950. A rapid vat-side test for assaying toxaphene in cattle dips.
U. S. Bur. Ent. and Plant Quar. ET-285. 9 pp., illus.
Figure 1.--Improved. syringe hydrometer.
See text for explanation,
UNIVERSITY OF FLORIDA
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