226 ANALYTICAL CHEMISTRY. 



QUESTIONS. 



341. Why is sulphuric acid added to a solid substance when it is to 

 be examined for acids ? 



342. Mention some acids which cause the liberation of colorless, and 

 some which cause the liberation of colored gases when the salts of these 

 acids are heated with sulphuric acid. 



343. Mention an acid which is precipitated by barium chloride in 

 acid solution, and some acids which are precipitated by the same re- 

 agent in neutral solution. 



344. Which acids may be precipitated by silver nitrate from neutral 

 solutions, and which from either neutral or acid solutions? 



345. Mention some acids which form soluble salts only. 



346. Mention 3 soluble, and 3 insoluble carbonates, phosphates, 

 arseniates, sulphates, and sulphides respectively. 



347. Which oxides or hydrates are soluble, and which are insoluble 

 in water? 



348. Mention some metals, the solutions of which are precipitated by 

 soluble chlorides, iodides, and sulphides. 



349. State a general rule according to which most insoluble salts may 

 be formed from two other compounds. 



350. Why is it sometimes impossible to render a substance soluble in 

 order to test for the acid in the solution obtained ? 



36. DETECTION OF IMPURITIES IN OFFICINAL 

 INORGANIC CHEMICAL PREPARATIONS. 



General remarks. Very little has been said, heretofore, about 

 impurities which may be present in the various chemical prepa- 

 rations, and this omission has been intentional, because it would 

 have increased the bulk of this work beyond the limits con- 

 sidered necessary for the beginner. 



Impurities present in chemical preparations are either de- 

 rived from the materials used in their manufacture, or they 

 have been intentionally added as adulterations. In regard 

 to the last, no general rule for detecting them can be given, 

 the nature of the adulterating article varying with the nature of 

 the substance adulterated; the general properties of the sub- 

 stance to be examined for purity will, in most cases, suggest 

 the nature of those substances which may possibly have been 



