.1821.] of the Edinburgh Pharmacopeia. 189 



proportions are 8*4 parts of acid to 100 of salt.'* Notwithstand- 

 Hig your remark, you surely cannot suppose that in directing 

 these relative quantities, the College could be ignorant of the 

 proportion of the ingredients of muriate of soda. Permit me then 

 to remind you, that the numbers in the scale indicate the quan- 

 tity of sulphuric acid necessary to saturate a given quantity of 

 soda, but by no means the quantity of this acid necessary to 

 effect the decomposition of the muriate with the greatest suc- 

 cess and convevience. It must, I presume, for the moment have 

 escaped your recollection that sulphuric acid is much disposed 

 to form a supersulphate of soda, and consequently that if no 

 more acid be employed than is barely sufficient to saturate the 

 quantity of soda contained in the muriate, a considerable portion 

 •of the muriate will remain undecomposed. j' 



After many repetitions of the process, I may confidently assert 

 •that the proportions assigned in the Pharmacopoeia afford a 

 larger product of muriatic acid in a shorter period at a smaller 

 expense of fuel than those which you recommend as the requi- 

 site. 



Acidum Nitrosum. — I suspect that we can turn to Httle ac- . 

 •count the remarks which you have made on the process for 

 preparing this substance, as I am persuaded from ample expe- 

 rience that they are not correct either in regard to the quantity 

 of the product, or the condition of the acid which is obtained. 

 You have thought fit to condemn the proportions directed in the 

 PharmacopcBia as unproductive and injudicious on the result of 

 a solitary trial, w^iich you state in the following words : *^ I put 

 • into a retort 24 parts of nitre and 16 of sulphuric acid, and car- 

 ried on the distillation as long as nitric acid was produced. The 

 ; product was of a straw colour, evidently containing but very 



■ little nitrous acid, and its specific gravity was 1513 instead of 

 ; 1520, as stated in the Pharmacopoeia. It weighed 11*5 parts, 



Tvhereas 24 parts of nitre are capable of yielding 17 parts of acid, 

 provided sufficient sulphuric acid is employed to afford water , 

 enough to condense the nitric acid." The results which I have 

 had uniformly for many years are extremely different. The 

 .quantity of acid amounts to 15 parts; it possesses a full orange- 

 red colour ; and its specific gravity, never less than 1520, occa- 

 sionally (when the nitre has been previously well dried, an^ th^e 

 . sulphuric acid boiled) has been so high as 1540. ' . i'l^ 



1 cannot refrain from expressing my surprise at the folloWmg- 



■ paragraph : " I have already observed that the acid which I 

 - obtamed has only a straw colour instead of a red one, as the 



College seemed to expect, and I believe that w^henever this acid 

 has this red colour, it is owing to the presence of common salt 

 :m the nitre, the chlorine pf which partially decorpposes the 

 • nitric acid." ^^^'f^rt^^inUmiylri h lU ..^.a. 



Every chemist knows that nitric acid a6(j[tiir6s^ia,reH' colour by 

 the action of muriatic acid (not of chlorine as you by inadvert- 



