394 Mr. Warington o?i Chromic Acid in Voltaic Arrangements. 



nitric acid. Now as the dilute sulphuric acid in the zinc cell 

 of the battery remains the same in both cases, it will be only 

 necessary to show, by the constitution of the nitric acid and 

 the bichromate of potash, the relative value of these two oxi- 

 dizing ao-ents in terms of the quantities of the available oxygen 

 they contain, such oxygen combining with the hydrogen eli- 

 cited by the action of the dilute sulphuric acid on the zinc 

 element. 



Liquid nitric acid, of I'iS sp. gr., is composed of 74 parts 

 by weight of real acid and 26 of water, and these 74 parts 

 contain 32*9 of oxygen and 41*1 of binoxide of nitrogen, 

 which latter body is given off in a gaseous state, as soon as 

 the undecomposed nitric acid has become saturated with it, and 

 assumed a deep green tint. When liberated from the solution 

 the gas combines with the oxygen of the air, generating the 

 nitrous and hyponitric acids, the red noxious vapours which 

 render the use of this form of battery so inconvenient. There 

 must, I imagine, be also a considerable loss of power from this 

 evolution of gaseous matter. I am not aware to what extent 

 the decomposition of the nitric acid can be carried in Grove's 

 battery, for after the action has been going on about five 

 hours, an effect of endosmosis commences between the cells 

 through the pores of the biscuit earthenware, and the amal- 

 gamated zinc plates are attacked with rapidity and quickly 

 destroyed. Not expecting such an occurrence, I had left a 

 small battery in action, on one occasion, through the night, 

 and found in the morning, to my great annoyance, that the 

 whole of the zincs were destroyed, and the arrangement all 

 fixed together. 



Bichromate of potash is composed of 2 equivalents of chro- 

 mic acid, or 104 parts by weight, and 47"5 of potash, and 

 these 104 parts contain 80 of the green oxide of chromium 

 and 24 of oxygen. Consequently, to obtain the same quan- 

 tity of available oxygen as we have in the 100 parts of nitric 

 acid, supposing the decomposition of these to be complete, we 

 shall require 206*9 of bichromate : and to convert this into 

 the double sulphate of chromium and potash, or chrome alum, 

 275*8 of concentrated sulphuric acid will be necessary. These 

 proportions of materials are requisite, as it is the strong affi- 

 nities leading to the formation of chrome alum which give 

 rise to the energetic oxidizing action of this mixture. 



A number of experiments were tried, to ascertain whether 

 the action of a battery excited by the acid element described 

 would be sustained and continuous, and the results have fully 

 established that it is so. In the action of such a battery no 

 gaseous matter is given off, the oxygen of the chromic acid 

 combining with the hydrogen from the zinc cell to form water, 



