§ 36. SOLLTTON. 25 



weiglied quantity of the substance (100 or 200 grms.) in 

 the cylinder, shaking the mixture well so as to disengage 

 bubbles of air, and observing the volume occupied by 

 both the substance and the water ; the increased volume, 

 which represents that of the substance added, expressed 

 in cubic centimetres, divided into the weight of the sub- 

 stance taken, expressed in grammes, will nearly equal the 

 specific gravity. 



d. If the substance is soluble in water, some other liquid, 

 like alcohol or naptha, must be used. Determine the 

 specific gravity of the substance with reference to this 

 liquid, by the same rules as above, and tlien multiply the 

 result by the specific gravity of the liquid used, with ref- 

 erence to the common standard, water ; the product will 

 be the specific gravity of the substance with reference to 

 the same standard. 



c. The sj^ecific gravity of a substance may be deter- 

 mined roughly, but very expeditiously, as, for example, 

 of potatoes, by putting several samples in a shallow dish 

 containing a saturated solution of common salt, and add- 

 ing water with constant stirring, until the buoyant power 

 of the liquid is diminished to such a degree that half the 

 samples swim at the surface, and half sink to the bottom; 

 it can then be assumed, with sufticient accuracy for some 

 purposes, that the average specific gravity of the article 

 under examination is the same as that of the solution, 

 and this can be determined with the aid of the hydrome- 

 ter (§ 34, h), 



SOLUTION. 



36. In order that a substance may be analyzed accord- 

 ing to the methods described in the following pages, it 

 must be brought into solution if not already dissolved. 

 The solvents most commonly used are water, hydrochloric 

 acid, and nitric acid, for inorganic substances, and water, 

 2 



