QUESTIONS AND ANSWERS 15 



which is soluble in even very dilute ammonia water, but insoluble 

 in nitric acid. 



(b) Add a few drops of 1 part of brucine in 300 parts of 5 per 

 cent, dilute sulphuric acid, then add some concentrated sulphuric 

 acid by pouring carefully down the side of the test tube and a red 

 color, changing to yellow, is produced at the line of contact. 



(c) Add hydrogen sulphide or ammonium sulphide to the solu- 

 tion and a black precipitate of lead sulphide, which is insoluble in 

 dilute acids or alkalies, results. 



Distinguish between hard water and soft water. Under what con- 

 ditions and how may hard water be made soft? 

 Hardness of water is due to the presence of mineral salts (cal- 

 cium, magnesium). Hard water does not readily produce a lather 

 with soap. Soft water contains very little or no inorganic matter 

 and readily produces a lather with soap. 



By boiling hard water, carbon dioxide escapes, the carbonates of 

 the metals are precipitated, and the water is rendered soft. By 

 distillation, hard water may be made soft. 



Describe a test to determine the hardness of water. 



For calcium: Pass a small amount of COj into the water, 

 CaHCOg will be thrown down, but is redissolved in an excess of 

 CO2. Upon boiling the clear solution, the excess of CO2 wiU be 

 driven off and CaHCOa will be precipitated. 



For magnesium: The addition of an alkali carbonate solution 

 causes a white precipitate of basic magnesiiun carbonate. 



Hard water does not readily produce a lather with soap, as does 

 soft water. 



Describe the oxyhydrogen blow-pipe. 



In this apparatus the oxygen and hydrogen are contained in two 

 separate receptacles. They are mixed just at the tip of the burner, 

 which consists of two tubes, one within the other. Through the 

 inner tube, oxygen is passed, and the outer one is connected with 

 the hydrogen reservoir. The hydrogen is first turned on and ignited, 

 then the oxygen is admitted. The resultant flame is intensely hot. 



HYDROGEN DIOXIDE 



What is hydrogen dioxide? Write the formula. 



It is a colorless liquid with an odor resembling weak chlorine 

 solution, a bitter astringent taste, and is unstable in concentrated 

 solutions, being easily decomposed with the liberation of oxygen. 

 Digitized by Microsoft® 



