24 § 35. ANALYTICAL MANIPULATION. 



ties corresponding to the different depths to which the in- 

 strument will sink in liquids of different densities, are 

 marked on a scale in the upper, slender part of the tube. 

 The temperature of the liquid whose specific gravity is to 

 be determined with the hydrometer should be as nearly 

 15° C. as possible. 



c. As there is a fixed relation between the degree of 

 concentration and the specific gravity of a solution of 

 any given substance, areometers are constructed, upon 

 whose scales the amount of the substance in 100 parts of 

 its solution is given, instead of the specific gravity of a 

 solution of that particular degree of concentration. Thus, 

 we have alcoholometers for mixtures of alcohol and water, 

 saccharometers for solutions of sugar, acetometers for so- 

 lutions of acetic acid, lactometers for milk. 



35. a. — To determine the specific gravity of a solid^ we 

 may Aveigh it first in the air, and then while immersed in 

 water, and suspended from the arm of the balance by a 

 fine thread or hair. The difference between these two 

 weights, divided into the Aveight of the body in the air, 

 will give its specific gravity. 



h. Or, if the substance is in the form of a powder that 

 is insoluble in water, we may weigh it first by itself in 

 the specific-gravity bottle, then fill the bottle with water, 

 as in § 34, a^ and weigh again. The difference between 

 the weights of water that the bottlq will hold, xcith and 

 without the substance in it, which is the weight of a vol- 

 ume of water equal to that of the solid substance, divided 

 into the weight of the substance itself, will give its spe- 

 cific gravity. 



c. Or, taking advantage of the fact that a cubic centi- 

 metre of water weighs very nearly one gramme at com- 

 mon temperatures, we may make a rough determination 

 of the specific gravity by filling a 500 c.c. graduated cyl- 

 inder exactly up to the 250 c.c. mark, then putting a 



