580 
ON DILUTED NITRO-HYDROCHLOEIC ACID. 
BY WILLIAM A. TILDEN, B.SC., F.C.8., LEMONSTRATOR IN THE SOCIETY’S 
LABORATORIES. 
Nitro-hydrochloric acid is a preparation found in all the pharmacopoeias. 
But the liquids designated by this somewhat indefinite title differ very notably 
in strength and in composition. This arises partly from the circumstance that 
the nitric and hydrochloric acids recommended by the different pharmacopoeias 
contain different percentages of real acid, partly because they are mixed in 
different proportions and in different ways. In some cases the undiluted acids 
are mixed and preserved in that state ; in others, as in the British Pharma¬ 
copoeia, they are diluted after a certain prescribed interval, and in yet others 
they are diluted with water at the time of mixing. 
In the British Pharmacopoeia of 1867, nitric acid (sp. gr. P42) and hydro¬ 
chloric acid (sp. gr. IT6) are directed to be mixed together in the proportion 
of three fluid ounces of the former to four fluid ounces of the latter, twenty- 
four hours previously to adding the water. The intention obviously acted 
upon in giving these directions is to permit the chemical reaction entered into 
by the acids to proceed as far as possible towards completion. 
Any one who has prepared the acid according to the instructions of the British 
Pharmacopoeia has, of course, witnessed the change of colour and the evolution 
of permanent gas which always take place in that operation. That the re¬ 
action of the undiluted acids gives rise to permanently gaseous products and 
consequently,, if the experiment be conducted in the usual way, to loss of ma¬ 
terial, is apparent from the coloured atmosphere of the bottle and from the 
acid dew which films the table upon which it stands. It is also obvious that 
this loss must be variable in amount, according to the circumstances under 
which such operation is conducted. Thus when a bottle no larger than is 
necessary to contain the whole of the liquid is employed, a very considerable 
deficiency must be the result; wheu a capacious mixing-vessel is used, the loss 
is smaller, from the fact that the gaseous resultants partly remain in the bottle 
and are absorbed again on the addition of the water. Temperature must also 
have an important influence; in the summer-time or in a warm locality, the 
action will proceed more rapidly and to a further limit, and the effect of this 
will be the production of a greater quantity of the gaseous emanation, which 
will also occupy a larger volume. 
The experiments about to be detailed were undertaken with the view of 
ascertaining, first, if the loss encountered from these causes could proceed to 
an extent that would be of importance ; and, secondly, if the composition of 
the dilute acid produced by the present official process differed perceptibly from 
that of the dilute acid prepared by the hitherto usual plan, namely, by the 
addition of the water simultaneously with the intermixture of the acids. The 
following results illustrate the points alluded to:—Two acids were taken of a 
strength nearly approaching that indicated by the Pharmacopoeia. They were 
mixed in the proportions ordered, allowed to stand during twenty-four hours in 
a stoppered Winchester quart (i. e. in a vessel capable of holding about ten 
times the quantity), and the next day were diluted and at once tested. 
Six fluid drachms required for neutralization 808'64 grain-measures of the 
volumetric solution of soda. Half the quantity was prepared in the same way 
in a Winchester quart. Of this, six fluid drachms took 828‘69 grain-measures 
of the standard soda. 
When the same acids were diluted before mixing, so that no preliminary de¬ 
composition was permitted, and tested in a similar way, it required 929 grain- 
measures to saturate six fluid drachms. 
