ESTIMATION OF NITRITES IN THE PRESENCE OF NITRATES. 201 
pills, in packing them up, and in sending them home to the customer. Some well-digested 
scheme for regulating the profits on medicines dispensed by chemists was much 
wanted. 
Mr. Atherton (Nottingham) had recommended the aqueous solution to prescribers in 
his neighbourhood, and they had adopted it. 
Mr. C. F. Palmer alluded to cases which had come under his observation in connec¬ 
tion with artificial chalybeate waters prepared by himself. On some occasions these 
waters had thrown down a red precipitate of hydrated peroxide of iron, but by exposure 
to solar light it had redissolved, and the solution had become almost colourless again. 
Was this also a case of reduction to a lower degree of oxidation ? 
Dr. Parkin' sox thought that in the case just stated the free citric acid mentioned had 
acted upon the precipitate. 
ON THE ESTIMATION OF NITRITES IN THE PRESENCE OF 
NITRATES. 
BY CHARLES R. C. TICHBORNE, F.C.S., ETC. ETC., 
CHEMIST TO THE APOTHECARIES’ HALL OP IRELAND. 
When I undertook the task of working out the best process for estimating 
nitrites, I thought that the problem would be one of extreme simplicity, and 
never calculated upon the numerous difficulties with which this project was 
attended. I have carefully gone through the modes recommended by other ex¬ 
perimenters (of which there have not been many), and have also tried numerous 
original plans. From very few of these have I succeeded in getting accurate 
results. Of course, I now refer to direct modes of estimating nitrites, more 
particularly in the presence of nitrates. The difficulties are as follows :—1st. 
All the processes of estimating nitrites directly must be essentially processes of 
oxidation, as we are not acquainted at present with any available precipitant.* 
Therefore arises the difficulty of estimating this compound by oxidation in 
the presence of a powerful oxidizer, i.e. nitric acid. We have no available pre- 
cipitant for this latter acid either, by which we could dispose of it. 
2nd. Another prolific source of error in the estimation of nitrites is one 
which seems to have been completely overlooked. It is the fact that at the 
slightest elevation of temperature nitrous anhydride, or nascent nitrous acid, 
is partially decomposed and oxidized into nitric acid, when in the presence of 
water—that is, at the expense of that substance :— 
3 N 2 O s + H 2 O = 2 TIN 0 3 -f 4 NO. 
Experiments proving this will be referred to further on. 
The process recommended by Peligot, Lang, Jahresb. 1862, p. 581, is not ap¬ 
plicable to the examination of nitrites containing nitrates. A Iso, the long di¬ 
gestion at an elevated temperature (twelve hours at 86° to 104° Fahr.) is inad¬ 
missible. Lang says he got results only *6 per cent, out, but I think he must have 
worked with pure nitrite of sodium.f Feldhaus speaks against this process. 
In his experiments he seems to have got the results too high; the specimens of 
nitrite probably contained nitrate. This process seems, in my hands, to give 
results too low, after the nitrate had been correctly accounted for. The urea 
* Nitrate of silver, tlie most insoluble salt, if we except the cobalt yellows (basic potassio* 
cobaltic nitrite?), is readily soluble in water, unless the water is at a very low temperature. 
Whether the cohalt yellow is available for the estimation of nitrites, is the subject cf some 
experiments at present unfinished. 
f A known quantity of dried peroxide of lead is added to a diluted solution of the nitrite to 
be analysed, and the solution mixed with acetic acid. The whole is warmed for twelve' hours ; 
—the weight of peroxide dissolved corresponds to the nitrous acid—1 at. peroxide = 1 at. nitrous 
acid (2Ph 2 Oo + 2HN Oo = Pb 2 No 0 6 + Pb 2 H o 0 2 ). 
VOL. VII. 
P 
