420 Prof. It. Bunsen's Spectral- Analytical Researches. 



theoretically deduced in 1 above, and to be composed of the 

 following proportions by weight : — 



Potassium dichromate . . 1 part. 

 Hydrated sulphuric acid . 2 parts. 

 Water 12 „ 



This liquid does not, when used, give rise to the formation of 

 chrome alum ; in contact with zinc it is coloured green ; it dries 

 up to a crystalline mass, which consists of sulphates of chromium, 

 potassium^ and zinc. By boiling with a large quantity of water 

 a precipitate is formed having the composition 2Cr 2 3 .3S0 3 . 

 Zinc, even when impure, dissolves in this liquid without evolu- 

 tion of gas and with an extremely bright surface*. 



In order to prepare 10 litres of this exciting liquid, 0*765 

 kilog. of commercial pulverized potassium dichromate (which 

 usually contains 3 per cent, of impurities) are added, with con- 

 stant stirring, to 0*832 litre of sulphuric acid, sp. gr. 1*836; 

 when the production of chromic acid and potassium sulphate is 

 complete, 9*2 litres of water are poured, in a thin stream, into 

 the mixture. The liquid thus becomes gradually warmer, and 

 the crystalline precipitate is entirely dissolved. In the researches 

 to be described, the exciter for this liquid consisted of a rod of 

 the densest gas-coal, 4 centims. broad and 1*3 centim. thick, 

 and a rolled zinc plate 4 centims. broad by 0*5 centim. thick, the 

 latter being covered with a film of wax, with the exception of the 

 surface turned towards the coal rod; this surface was amalga- 

 mated. The zinc and coal were each immersed to a depth of 12 

 centims. in the liquid. The distance between the coal and zinc 

 varied, according to circumstances, from 3 to 10 millions. Rather 

 unsatisfactory results, as regards duration and constancy of cur- 

 rent, are obtained with this liquid if cells are employed of the 

 shape and size ordinarily used in Grove's or the zinc-carbon bat- 

 tery. This is accounted for by the fact that in the nitric acid 

 of those batteries there is stored up a much larger quantity of 

 oxygen, which may be used for depolarization, than in an equal 

 weight of the chromic liquid, and that therefore a proportionately 

 much larger quantity of the latter must be used in order to pro- 

 duce an equal effect. The cells of the chromic-acid battery must 

 therefore be of three or four times the capacity of those of Grove's 

 battery. The best shape for these cells is that of high narrow 

 cylinders^ which extend over no -greater surface than equally 

 powerful elements of the ordinary clay cells. The column of 

 liquid, containing about 1*6 litre, reaches to a height of 0*28 

 metre, and has a diameter of 0*088 metre. The zinc-coal pair 

 is immersed in the liquid to half its height only, and presents an 



* This liquid is very useful for removing the rust from metals. 



