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TRANSACTIONS OF THE SECTIONS. 55 
imagined, may be due either to the more rapid decomposition or more speedy 
evaporation and expulsion of the cyanogen compound from the furnace at the 
higher temperature which is known to prevail in the hearth when manufacturing 
grey iron, 
On the Dissociation of Nitric Acid by various means. 
By P. Branam, F.C.S., and J. W. Gatenovse. 
The first series of the following experiments was performed by passing the 
vapour of nitric acid of sp. gr. 1°48 through tubes exposed to various temperatures, 
it being found that the higher the temperature to which the vapour was exposed 
the greater was the percentage of HNO, decomposed, and also that the dissociation 
which occurred at high temperatures was more complete than that which took 
place at lower temperatures. 
By passing nitric-acid vapour through molten tin, 2°51 per cent. of the vapour 
issuing from the retort was decomposed, and 0-7 per cent. of gasevolved. This gas 
contained 95 per cent. of oxygen, the remainder, after explosion with hydrogen, 
being nitrogen. 
By passing the vapour through molten lead from 21:28 to 31:84 per cent. was 
dissociated, and from 2°96 to 4:1 per cent. of gas evolved. 
The vapour being heated by means of a Bunsen’s burner, 54:09 per cent. was 
decomposed and 8:05 per cent. of gas evolved, 
The heat from a charcoal fire, the vapour being conducted through a hard glass 
tube, decomposed about 65 per cent, of acid* and yielded 10:44 per cent. of gas, 
With a charcoal fire, the vapour being passed through a porcelain tube, 89:7 per 
cent. was decomposed and 13:23 per cent. of gas evolved. 
In the second series, conducted by passing nitric acid through a clay pipe exposed 
to various temperatures, that of a T-shaped Bunsen decomposed 71:72 per cent., 
yielding 9°13 per cent. of gas. 
Using a clay pipe heated with charcoal, 83:4 per cent. suffered decomposition, 
yielding 11:5 per cent. of gas. 
In these two series of experiments the percentage of oxygen contained in the gas 
collected gradually decreased from 95 per cent. in the case of molten tin to 78:4 per 
cent. in the case of the charcoal fire, the remainder consisting of nitrogen and 
nitrous oxide. Nitrous acid or tetroxide of nitrogen was produced largely in every 
case, but was absorbed and estimated separately. 
The proportions of O, N, and N,O could not be determined with exactitude ; but 
in the case of the T-shaped Bunsen the amount approximated to 79°6 per cent. of O, 
10 of N,O, and 10:4 of N. 
It thus appears that the whole of the oxides of nitrogen are produced during the 
dissociation of nitric acid by heat; an approximation to the reactions occurring may 
be expressed by the following formula :— 
SHNO, =4H, 0+2NO,+N, 0,4+N, 0+N,+0,,. 
Experiments were also undertaken by us to ascertain whether any decomposition 
of nitric acid occurred during the act of boiling. 
Pure nitric acid is not decomposed ; but if it contains nitrous acid, then decom- 
position proceeds till the whole of the N, O, is expelled, when no further change 
ensues. 
‘The decomposing action of sunlight on nitric and nitrous acids was also studied. 
Pure nitric acid placed in a full bulb, sealed, and exposed several days to sun- 
light, remained colourless, and without evolution of gas ; but the same acid exposed 
to sunlight in a sealed tube only partially full was powerfully decomposed, yielding 
over 1 per cent. of nitrous acid and a considerable amount of gas. 
This action in sealed tubes is not continuous; for when the nitrous acid formed 
attains to about 2 per cent. of the quantity of nitric acid present, all decomposition 
ceases. 
* The amount could not be accurately determined, as the heat fused the glass tube, and 
a little of the acid was lost, 
