HYDROSTATICS. 



equal bulk of water weighing 253 ; and 

 so the specific gravity of the water is 

 about a fourth greater than that of 

 the spirit. 



Upon this principle the Hydrometer 

 is constructed : its name is derived from 

 two Greek words signifying: measure of 

 water. There are various kinds of hy- 

 drometers. One is a glass or copper 

 ball with a stem, on which is marked 

 a scale of equal parts or degrees. The 

 point to which the stem sinks in any 

 liquid being; ascertained, and marked 

 on this scale, we can tell how many 

 degrees any other liquid is heavier or 

 lignter, by observing the point to which 

 the stem sinks in it. Another and 

 a very simple Hydrometer is formed 

 by preparing a number of hollow glass 

 beads of different weights, but the 

 proportions of which are known, and 

 the beads marked accordingly ; they are 

 then successively dropped in the fluid to 

 be examined, until one is found which 

 neither sinks nor comes up to the sur- 

 face, but remains at rest, wherever it is 

 placed in the liquid. You thus ascer- 

 tain that the liquid is of the same speci- 

 fic gravity with this bead. If the same 

 bead be dropt into another liquid, and 

 sinks, that liquid must be lighter than 

 the first ; if the bead comes to the top, 

 the second liquid is heavier than the 

 first ; and by trying the liquid with the 

 other beads until one is found which 

 neither sinks nor floats, you ascertain 

 the relative weight of the liquid by the 

 number of the bead. 



A Hydrometer of 

 great delicacy and pe- 

 culiarly useful for mea- 

 suring: the specific gra- 

 vity of different waters, 

 and thereby ascertain- 

 ing their degrees of pu- 

 rity, consists of a ball of 

 glass three inches dia- 

 meter, with another , 

 joining it and opening ^ 

 into it, of one inch di- 

 ameter, B and C, (Jig. 

 16.) and a brass neck d, 

 into which is screwed 

 a wire ao, about ten 

 inches Ions: and l-40th 

 of an inch diameter, 

 divided into inches and 

 tenths of an inch. 

 The whole weight of 

 this instrument is 4000 

 grs. when loaded with 

 shot in the lower ball. 



It is found that when plunged into water 

 in the jar, a grain laid upon the top 

 a makes it sink one inch ; therefore 

 a tenth of a grain sinks it a tenth of an 

 inch. Now it will stand in one kind 

 of water a tenth of an inch lower than 

 in another, which shows that a bulk of 

 one kind of water equal to the bulk of 

 the instrument weighs one-tenth of a 

 grain less than an equal bulk of the 

 other kind of water ; so that a differ- 

 ence in specific gravity of one part in 

 forty thousand is thus detected. This 

 weight of 4000 grs. is convenient for 

 comparing water ; but the quantity of 

 shot in the lower ball may be varied, 

 so as to make it lighter or heavier, and 

 so adapt it to measure the specific gra- 

 vities of lighter or heavier liquids. It 

 will always be an accurate and very 

 delicate measure for liquids of nearly 

 the same weight. Indeed its delicacy 

 is so great, that an impurity too slight 

 to be detected by any ordinary test, or 

 by the taste, will be discovered by this 

 instrument. 



The Areometer invented by M. De 

 Parcieux of Paris, and so named from 

 two Greek words, signifying measure of 

 weight, is more simple and affords a very 

 accurate comparison of different liquids. 

 It is only a different form of the in- 

 strument just described. A glass phial, 

 about two niches or two inches and a 

 half in diameter, and seven or eight 

 long, with a plane or round bottom, is 

 corked tight, and into the cork is fixed 

 a perfectly straight wire of about l-12th 

 inch diameter, and thirty inches long. 

 The phial is loaded with shot, so as to 

 make it sink in the heaviest liquid to 

 be examined, leaving the wire just 

 below the surface. There is a cylinder 

 of glass, about three or three and a 

 half inches diameter, and three or four 

 feet long, with a scale of equal parts 

 on the side. The liquor to be tried is 

 put in this ; and the scale marks the 

 point to which the top of the wire sinks. 

 This instrument is so sensible, that if it 

 stands at any point in water of the 

 common temperature, and the sun's 

 rays fall upon the water, the wire will 

 sink several inches, from the slight in- 

 crease of heat causing an increase of 

 bulk, and consequently a diminution of 

 relative weight in the water ; and it will 

 rise again when carried into the shade. 

 A pinch of salt or sii2:ar thrown in 

 makes it rise some inches, and a little 

 spirits poured in makes it sink. "With 

 one of these instruments, weighing 



