64 REPORT—1858. 
On a new Method for the Quantitative Estimation of Nitric Acid. 
By Dr. Pucu. 
The author found that the action of nitric acid upon protochloride of tin, in a solu- 
tion strongly acidified with chlorhydric acid, produced perchloride of tin and am- 
monia according to the formula (NO,+8SnCl+8HCI=NH,+ 8SnCl+5HO) ; but 
that the reaction was not completed, at the boiling-point, under ordinary pressure, 
even when maintained at this point for several hours. The results obtained at ordi- 
nary pressure with long-continued boiling, presented no constant value, and the 
maximum degree of oxidation afforded did not amount to quite three-fourths of the 
whole quantity required by the formula given above. 
But on heating the mixture in an oil-bath, in glass-stoppered bottles, or in herme- 
tically sealed tubes, to 160° Centigrade, the reaction was completed in 10 minutes. 
Upon this reaction he proposed to found two methods for the determination of nitric 
acid, either one or both of which could be used with the same quantity taken for 
analysis. 
(a.) First Method.—This consists in ascertaining how much protochloride of tin is 
converted into perchloride during the reaction. 
(b.) Second Method.—This takes adyantage of the ammonia formed during the 
reaction. It is separated by distillation with an excess of fixed alkali and the di- 
stillate caught in a receiver, with a known quantity of acid, which is then treated 
according to Peligot’s method for estimating nitrogen. 
In the first method the amount of protochloride of tin converted into perchloride by 
the nitric acid is ascertained by triturating equal quantities of the tin solution before 
and after the reaction with the nitrate to be examined. This is done by ascertaining 
how much of a solution of known strength of bichromate of potash will be converted 
into the sesquioxide of chromium by a given quantity of the protochloride solution, 
according to the formula 
2(CrO,)+8HCl43'SnCl=Cr, O,4+3HO+3S5nCl,, 
the point of complete chloridation being ascertained according to String’s method by 
the intensely blue colour produced, on the liberation of free iodine, from iodide of 
potassium, in the presence of starch, by the first trace of chromic acid over that re- 
quired to chloridate the tin. 
From the reactions 
NO,+8(HCl]+SnCl)=NH,+8SnCl,4+5HO and 
KO.(CrO,),+3(HCl+SnCl) = KO+ Cr,0,;+3(HO-+SnCl,), 
we get 
NO, corresponding to 2 (KO.(CrO,), ) ; : 
and hence, without knowing the value of the strength of the protochloride solution, ex- 
cept in terms of the bichromate used, we get the amount of nitric acid present. Thus 
Let A=weight of bichromate in a unit of volume of the solution used ; 
and N=the number of these units which corresponds to the whole tin solution 
used in a determination ; 
n=the number of the same units corresponding to the unoxidized portion 
of the tin, after the reaction with the nitric acid ; 
then N—n=the number of units of volume of the bichromate solution which cor- 
respond to the nitric acid deoxidized ; 
(N—n)a=weight of the bichromate corresponding to the nitric acid deoxidized ; 
is NO, 
s(N—2)4X 0 (G0,, 
The quantity (a) may be taken so small in relation to the unit of volume in which 
it is dissolved, that a quantity of that solution corresponding to *00005 grm. nitric 
acid may be read off on the burette with ease. Such was the case with the five con- 
secutive analyses below :— 
Nitric acid taken..........-. °00539 grm. 
Nitric acid found............ "00541 
=NO, present. 
” ” eveeseorese “00541 
» 9 ee ee 00541 
” ” eetenecee. ae °00532 
”» ” seoeetrncceete 00546 
