56 
vessel, so that the fumes given off are not mixed with the 
atmosphere, I have found that the gas evolved appears to 
be a mixture, neither free from the red colour of nitrous 
acid, nor having the property of becoming fully coloured, as 
the binoxide of nitrogen would when mixed with air ; it is, 
therefore, an uncertain mixture. I have found it most 
advisable to ascertain the proportionate consumption of zinc 
and nitric acid by direct experiment. In doing so I found 
that the dilution of nitric acid had much effect on the 
economy, and that it was more economical to use a mixture 
of equal parts of nitric and strong sulphuric acid by about 
35 per cent, than to use nitric acid alone. The following 
are the results of my experiments : — A porous cell was 
charged with 763 grains of nitric acid; the galvanometer 
included in the circuit at first indicated 76 grains per hour; 
the action was continued for three hours, when the galva- 
nometer declined to 27. The nitric acid was then considered 
exhausted. The zinc, electrolitically dissolved, would be 
about 180 grains. The specific gravity of the nitric acid 
used was 1.315, corresponding to about 300 per cent, of 
pure acid. Such acid costs about 6d. per lb ; so that the 
quantity of nitric acid correspondent to the consumption of 
1 lb. of zinc would thus cost 2s. But, according to the 
experiments where nitric and sulphuric acids were used 
together, the cost might be Is. 3d., or possibly the acid might 
be obtained so much cheaper as to reduce the cost to Is. 
And, to return to the former method of calculation, we 
have, with a nitric acid battery, an intensity of 16 instead of 
5.5, and 5.5 X 100 = 16 X 34.37. We have, therefore, 
to use 34 instead of 100, and the consumption of zinc would 
be 3,062 grains per hour, which will cost about 3d., and at 
the least 5d., for nitric acid, together 8d. We thus find that 
the cost of three forms of battery calculated to produce the 
same effect is very similar, being respectively 7d. for Smee's, 
