ZiV CHEMISTRY. 99 



The standard gallon of the United States weighs 

 8.3389 Ibs. of distilled water. 



H a : H 2 O : : x : 8.3389 Ibs. 

 2 : 18 : : x : 8.3389 Ibs. 

 9 x = 8.3389 Ibs. 

 x = .9265 Ib. (H). 



1 8. In decomposing H 3 O, 65 parts by weight ofZn yield 

 2 parts by weight 0/~H. How much Zn must be employed 

 to obtain 100 Ibs. 



If we look at the equation 



H 2 SO t + Zn = ZnSO 4 4- H 2 , 



we see that 



H 3 signifies 2 parts by weight of hydrogen, 



H 2 O 18 



S " 32 



ZnSO, 



O t " 64 ' " oxygen, 



H 2 SO 4 u 98 " ' " sulphuric acid, 



Zn " 65 " l " zinc, 



41 water, 

 ' " sulphur, 



zinc sulphate. 



The equation, therefore, shows that 98 parts by weight 

 of sulphuric acid added to 65 parts of zinc will form 161 

 parts of zinc sulphate, and, decomposing 18 parts of 

 water, liberate 2 parts of hydrogen. For every part of 

 H we must have $- parts of Zn : hence, to obtain 100 

 Ibs. of H we should need 100 Ibs. x * = 3250 Ibs. Zn. 

 In a similar way we can find the amount of each of the 

 other constituents needed. 



19. How much KC1O 3 would be required to evolve suf- 

 ficient O to burn the H produced by the decomposition of 2 

 Ibs. ^H 2 O? 



(See Key, page 61, Question 37.) 



