82 APPLIED SCIENCE 



WEIGHT AND SPECIFIC GRAVITY OF LIQUIDS (Continued) 



Water. The weight of fresh water is in practice usually 

 assumed as 62^ Ibs. per cubic foot. But 62*4 would be 

 nearer the truth at ordinary temperatures, about 70; or 1 

 Ib. = 27.759 cu. in. 



81. Hydrometer. The common method of determining 

 the specific gravity of liquids is by means of the hydrometer 

 (Fig. 52). This instrument consists of a 

 glass tube with mercury or lead shot in the 

 bottom to keep it in the water. A scale is 

 graduated on the narrow stem reading either 

 directly or indirectly into specific gravity 

 reading. The scale is graduated by placing 

 it in liquids of known strength and marking 

 the level of the liquid on the stem. It is 

 usual to have two separate instruments, one 

 for light ^^3, O n which the mark is near 



FIG. 52. Hy- 

 drometer. 



the bottom of the stem, and one for heavy liquids, on which 

 it is near the top. 



