14 VETERINARY STATE BOARD 



filings may be substituted for the zinc, and sulphuric acid for the 

 hydrochloric acid). 

 What element occurs in all acid compounds? Describe the element. 



Hydrogen. See description given above. 

 Find how many grammes of H may be released from HCl by 260 

 grammes of Zn. How many grammes of HCl are neces- 

 sary? [Atomic weight of Zn = 65, of CI = 3S-5-] 

 65 : 2 = 260 : X. Z = 8 grammes of H. 

 73 : 2 = Z : 8. X = 292 grammes of HCl. 



WATER 



Give the composition of water (a) by volume, (b) by weight, and (c) 

 give its molecular weight. 



(a) Two volumes hydrogen and one volume of oxygen. 



(b) Two parts of hydrogen and sixteen parts of oxygen, 

 (e) 18. 



If six volumes of hydrogen and two volumes of oxygen are placed 

 together and the electric spark passed through them, will 

 the volume be increased or diminished, and to what extent? 



The volume will be diminished from 8 to 2, because four volumes 

 of hydrogen would unite with the two of oxygen and form 2 mole- 

 cules of water, leaving two volumes of hydrogen free. The volume 

 of the water formed is so small that it may be disregarded in the 

 calculations. 



Describe one way in which water can be decomposed and two ways in 

 which it can be formed. 

 Decompose by acidulating slightly with sulphuric acid and pass 

 an electric current through it. Water can be formed by passing 

 an electric spark through a receptacle containing two volumes of 

 hydrogen and one volume of oxygen ; also by burning hydrogen in 

 the presence of oxygen, as in the air. 



State the means by which water may be purified. Describe one of 

 these ways. 

 Filtration, distillation and precipitation. 



Filtration is accomplished by allowing the water to percolate 

 through layers of charcoal and sand, or by forcing it through a 

 very thick porcelain material with small pores. 



Describe a test to show the presence of each of the following in water: 

 (a) chlorides, (b) nitrates, (c) lead, 

 (a) Add silver nitrate : a white, curdy precipitate is produced 



