SOLUTION OF PEENITRATE OF IRON. 
417 
Further, we would draw attention to the necessity of being 'careful to ensure 
complete peroxidation before proceeding finally to precipitate the oxide. This 
may be readily ascertained, either by the addition of ammonia to a small quan¬ 
tity of the solution, freely diluted, in order to determine the absence of the 
black oxide in the resulting precipitate, or, by the addition of red prussiate of 
potash to another portion of the solution, likewise diluted, in which case no 
blue coloration must be perceptible. 
If it be found, upon the application of these tests, that the iron has not yet 
been entirely peroxidized, increased heat, or, should that fail, a fresh supply of 
acid will produce the desired effect. 
Yours sincerely, 
Edinhurgh, December l^th, 18G6. T. AND II. Smith. 
SOLUTION OF PERNITEYTE OF IRON. 
TO THE EDITOR OF THE PHARMACEUTICAL JOURNAL. 
Sir,—I was much pleased to see, in the November Journal, the description of 
a new process originated by the Messrs. Smith, for the preparation of solution 
of pernitrate of iron ; and one which, if generally adopted by chemists, would 
conduce to a greater uniformity in the production of an article so unstable and 
variable in its nature, as that prepared by the recognized formula. 
It not unfrequently happens that customers though apparently convinced, 
after explanation, of the superiority of the light-coloured preparation, will again 
have recourse to the darker-coloured and sometimes even turbid solution, more 
especially if the latter has been sent out by a house with an “ historic name.” 
The decomposition to which that prepared by the recognized formula is sub¬ 
ject, I believe altogether to arise from the use of an acid of insufficient strength. 
This may be excusable when Kerr’s formula is adopted, as in it the strength of 
acid is not stated, but will not apply to the B. P. process, as it distinctly 
states nitric acid to be of sp. gr. 1-5, and to contain 80 per cent, of anhydrous 
acid. When an acid of this strength is employed, the product is of a beautiful, 
transparent, reddish-brown colour, and not in my experience subject to change, 
though containing a minute quantity of protonitrate, which is necessarily pre¬ 
sent from the acid being insufficient in quantity to form the whole of the iron 
into pernitrate, and which will appear from the following proportion :— 
56 or 2 equivalents of iron require 54 or 1 equivalent of anhydrous nitric 
acid to form it into peroxide; consequently 437’5 parts of iron will re¬ 
quire— 
56 : 54 : : 437’5 : 421*8 pts. of anhydrous nitric acid. 
56 or 2 equivalents of iron, converted into peroxide, require 162 or 3 equi¬ 
valents oPanhydrous acid to form pernitrate; consequently 437*5 will re¬ 
quire— 
56 : 162 : : 437*5 : : 1265*6 pts. of anhydrous nitric acid. 
To form 1 ounce of iron into pernitrate, 421*8 -f- 1265*6 = 1687*4 grs. of 
anhydrous acid is required. 
B. P. acid contains 80 per cent, of anhydrous acid, consequently— 
80 : 100 : : 1687*4 : 2109*25 grs. by weight of B. P. acid. 
To reduce this to fluid measure— 
1*5 : 10 : *. 2109*25 : 140fi*17 grs. 
Or 3 fluid ounces 1 drm. 42-,% minims is required to form 1 ounce of iron 
into pernitrate. 
