684 INDUSTRIAL APPLICATIONS. 



elements ; it only depends on the electromotive force of each couple, 



p 

 and on the number of equivalents concerned. 



P 



The work of a horse-power during an hour, or the horse-power- 

 hour, being 75x36,000 = 270,000 kgm., the number of chemical 

 equivalents corresponding to a horse-power is 



P 9-81 2-65 



- 270,000 = - io 6 , 

 p e e 



which for hydrogen, with an electrochemical equivalent of o-io35'io~ 4 , 

 is equal to 



2-65 x 10*35 2 7'42gr. 



This value for hydrogen would enable us to calculate the corre- 

 sponding weights of different bodies, provided the reactions were well 

 known; but it frequently happens that the effects are rather com- 

 plicated. This, for instance, is the case with nitric acid, which serves 

 as depolarizer in Bunsen's element. The passage of a coulomb 

 destroys then an equivalent, or a third of an equivalent, according 

 as the acid is transformed into hyponitric. acid, or into bioxide of 

 nitrogen ; we may then take as mean half an equivalent. We thus 

 find, for two elements of frequent use : 



EXPENDITURE FOR A HORSE-POWER-HOUR. 

 DanieWs Element (e=i). 



Kgm. 



Zinc (Zn = 33) ... ... =0-905 



Sulphuric Acid (SO 3 ,HO = 49) =i'344 



Sulphate of Copper (CuO,SO 3 + 5HO = 124-75) =3'42o 



Bunsen's Element (e=i'S). 



Kgm. 



Zinc (Zn = 33) =0-503 



Sulphuric Acid (SO 3 ,HO = 49) =0-746 



Nitric Acid (NO 5 ,4HO = 9o) =0-685 



The sulphate of zinc may be considered as a useless product in 

 both cases. It is possible, on the other hand, in DanielFs cell, to 

 reproduce the sulphate of copper from the copper thrown down, 



