August 1950 ET-290 
 
 United States Department of Agricultui^e 
 
 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 (J_), 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, jD) 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 a floa4 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 
 locations. 
 
 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 
 ordinary cylinder. 
 
 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. 
 
 Literature Cited 
 
 (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. 
 /P'rocessedUy 
 
Figure 1, — Improved syringe hydrometer. See text for explanation. 
 
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UNIVERSITY OF FLORIDA 
 
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