Chap. XIX,] 



DENSIMETER OF ROUSSEAU. 



20; 



Fl s fmeter De of 



float at zero on the scale. The water is now removed 

 from the tube, and in its place is poured one cubic 

 centimetre of the liquid whose density is to be 

 determined. The one cubic centimetre is 

 measured in both cases by means of a ps 



little pipette P, the markings (1 0) on 

 whose stem indicate the volume of one cubic 

 centimetre. The fluid, being denser than 

 water, will sink the densimeter. Let the 

 reading be taken. Suppose it be fifteen ; 

 that is, it displaces J^^-ths of a cubic 

 centimetre of water more than the distilled 

 water, which is taken as unity. As each 

 cubic centimetre equals one gramme, this 

 means that the liquid is T ^jths heavier 

 than the water, which equals 1 ; that is, its 

 density is 1'15. 



In practical medicine densimeters are in 

 constant employment. Thus one densimeter is con- 

 structed for urine, and is called a URINOMETER, and 

 another for milk, which is termed a LACTOMETER. The 

 urinometer sinks in distilled water to the top of the 

 stem, which is marked 1,000, and at corresponding in- 

 tervals down the stem are marked 1,005, 1,010, 1,015, 

 1,020, and so on. The specific gravity of urine is on 

 an average 1 '025, and, therefore, in urine the urinometer 

 should stand at the level 1,025. ISTow the value of the 

 determination of the specific gravity is not so much 

 in obtaining the absolute amount, as in being able to 

 observe variations in it, and relating these variations to 

 the causes which produce them. Thus, suppose an 

 average specimen of urine indicated a specific gravity 

 of 1'036, this indicates a less proportion of water, 

 which might be due to concentration of the urine or 

 to increased secretion of solid matters. In diabetes 

 the sugar secreted at once raises the specific gravity. 

 Consequently with a high specific gravity one would 



