1821.] Mr. Phillips's Reply to Dr. Hope. 29 



I now distilled a mixture of 24 parts of nitre and 24 of sulphu- 

 ric acid. The product was of a pale colour, of specific gravity 

 1499, and weighed 16 parts within a few grains. On comparing 

 it with the nitric acid procured in your mode, there was scarcely 

 a shade of difference in their colour. The whole quantity of 

 nitric acid, of specific gravity 1500, obtainable from 24 parts of 

 nitre, amounts to 17 parts ; so that a little more than ]-17th was 

 lost in the operation. 



Now the cost of 24 parts of nitre and 24 of sulphuric acid 

 being estimated at 144, that of 24 parts of nitre and 16 of sulphu- 

 ric acid will be 128, and the acid produced by the former 

 amounts to 16 parts, and that by the latter to 13*7 parts. It 

 follows, therefore, that 16 parts of pale acid obtained by using 24 

 parts of sulphuric acid cost less than as much red acid obtained 

 by using 16 of sulphuric acid, in the proportion of 144 to 149 ; 

 for 13-7 : 128 :: 16 : 149. This calculation is made on the sup- 

 position that red nitrous acid, of specific gravity 1534, is equal 

 in strength to pale acid of 1499, which, however, is far from 

 being the case; for, as already shown, both from theory and 

 experiment, the 3*2 parts of water which 16 of sulphuric acid 

 contain can yield only 12*7 of pale acid ; therefore, the cost of 

 your method is greater than that incurred by using one half more 

 sulphuric acid in the proportion of 161 to 144 ; for 12-7 : 128 :: 

 16:161. 



You do not seem to suppose that nitrous acid is applicable to 

 any one medicinal purpose which may not be as well answered 

 by using nitric acid ; but unless you are prepared to show this, 

 I think I have proved that your process is for several reasons 

 much less advantageous than that which Dr. Wollaston has 

 described, and I have quoted from him. Your process, from 

 the deficiency of water to condense the nitric acid, is less 

 economical ; and you incur some expense of fuel and in- 

 creased risk of breaking the retort, merely to render the acid 

 red ; and when this is done, it is to be rendered colourless by 

 incurring fresh expense of time, fuel, and the chance also of 

 breaking the vessel in which the operation is performed. 



Acidum Muriaticum. — With respect to this preparation I have 

 no hesitation in stating that I was in error in supposing that the 

 quantity of sulphuric acid which you employ is less economical 

 than that indicated by the scale as equivalent to the common salt. 

 The experiments upon which my present opinion is founded are 

 the following : 



According to your process, I mixed in a retort 10 parts of 

 sulphuric acid with 10 of common salt, and the requisite quan- 

 tity of water. The cost of the salt being estimated at 4, that of 

 the sulphuric acid will be 2, total cost = 6. When the opera- 

 tion was over, I tried the specific gravity of the muriatic acid, 

 and found it 1176, and the residuum weighed 13-45 parts. We 

 may, therefore, presume, that the whole of the common salt was 



