196 HYDROMETERS. 



surface of the liquid in which the hydrometer floal 

 gives either the specific gravity of the liquid, or its 

 percentage composition if the liquid is a mixture, 

 for instance, common spirit of wine, in which case th 

 hydrometer (alcoholometer) usually indicates the re- 

 lative amounts of pure alcohol and water in 100 parts 

 of the spirit. In other kinds of hydrometers the scale 

 has an arbitrary graduation, and its indications are 

 then referred to special tables, which supply the 

 quired information on the specific gravity or ' strength 

 of the liquid. 



For example, Baume's hydrometer sinks in water t< 

 the zero of the scale, but in concentrated sulphuric aci< 

 it sinks to the division marked 66. The distant 

 between the marks and 66 is divided into 66 eqiu 

 parts, each of which is called a degree. The specific 

 gravity of any liquid can then be found by means oi 

 the instrument with the help of the following rule 

 Subtract the number of degrees on the scale to whicl 

 the instrument sinks, from 144, and divide 144 by th< 

 difference: the quotient is the specific gravity of th< 

 liquid. For example, suppose the instrument has sun! 



in a liquid to 20 on the scale; then 



144 - 20 

 is the specific gravity of the liquid. 



22. Fountains. Efflux from Orifices. The Screw-Pr 

 peller. If an open vessel which contains a liquid 

 an orifice anywhere below the surface of the liquid, th 

 latter will escape through the orifice, in consequence 

 the action of gravity; if the orifice is not too near the 

 surface, the liquid will be forced out with a certain 

 amount of pressure, and will form a jet. If the orifice 



