STATE GEOLOGIST. 119 



» gravity of brine is by weighing a given bulk of it with a deli- 

 cate balance. The most convenient method, however, is by 

 means of a hydrometer, and this is sufficiently accurate for 

 most practical purposes. A hydrometer is an instrument gen- 

 erally made of glass, in the shape of a tube closed at both 

 ends with a large bulb blown in it, and a weight attached at 

 the lower end. The tube is graduated above the bulb, in such 

 a manner that when the instrument is placed in pure water it 

 sinks to a mark designated 0, and when placed in a liquid 

 heavier tl*an water, it sinks to some mark below the first, 

 against which is the figure which designates the true specific 

 gravity of the fluid. In Beaume's hydrometer, which is the one 

 most used for general purposes, the figures on the scale do not 

 designate the specific gravity directly. The scale is graduated 

 from to some arbitrary point which reads 30° or 40" — the 

 intervening space being equally, or nearly equally, divided, so 

 that the specific gravity can only be. known from it by a 

 calculation. 



The hydrometer, however, which is mdst convenient for ex- 

 periments with brine, is the one which marks 0° when immersed 

 in pure water, and 100° when immersed in saturated brine. 

 This instrument is called a salometer. The number of degrees 

 indicated upon the salometer, therefore, is the per centage of 

 saturation possessed by the brine. We may speak of 25" on 

 the salometer or 25 per cent, of saturating, 



It must be distinctly understood, that 25 per cent, of satura- 

 tion does not mean that 25 per cent, of the brine is composed 

 of salt. Twenty-five per cent, of salt produces 100 per cent, 

 of saturation — and this happens to be 25° on Beaume's hydrom- 

 eter. 



It is apparent, therefore, that the specific gravity of a brine, 

 the readings of the hydrometer and salometer, and the per cent- 

 -agc of salt, are all different expressions for the same thing, 

 which may also be expressed by the number of gallons of brine 

 required for a bushel of salt of 56 lbs. As it is often desirable 

 -to convert these expressions into each other, I have calculated 



