1821.] The Edinburgh Pharmacopaia. 59> 



excess renders the use of large retorts necessary, and thus 

 greatly increases the expense of the operation. 



The acetic acid actually produced scarcely merits the name 

 of ** strong " by which it is described. I find that its strength 

 is to that of distilled vinegar only about as three to one ; added 

 to these objections, its odour is extremely unpleasant arising from 

 empyreuma. 



Another circumstance to be noticed is, that there is left in the 

 retort a mixture of sulphate of lead and peroxide of iron, from 

 which it is very difficult to clear it for a second operation. 



These difficulties are all easily remedied. Let the acetate of 

 lead be decomposed by sulphate of soda; the sulphate of lead 

 being rejected, crystallize the acetate of soda, and decompose it 

 by sulphuric acid. The acid thus obtained is not at all empy- 

 reumatic; the sulphate of soda left in the retort is easily dissolved, 

 and serves for a second decomposition ; the quantity of sulphu- 

 ric acid required is only 2*6 parts instead of the 6-4 parts con- 

 tained in the sulphate of iron directed. It is indeed true that 

 there is the additional process of crystallizing the acetate of 

 soda, but this is more than compensated for by omitting the 

 preparation and drying of the sulphate of iron. 



Acidum Muriaticum, — Equal quantities of sulphuric acid and 

 common salt are directed to be employed in the preparation of 

 this acid. It will be seen by Dr. WoUaston's scale that the 

 requisite proportions are 84 parts of acid to 100 of salt. 

 , Acidum Mtrosum. — This acid is directed to be distilled by 



decomposing 24 parts of nitre by 16 of sulphuric acid ; and it 

 may be remarked that the product is not strictly speaking 

 nitrous acid, but a mixture of it and nitric acid, the latter being 

 unquestionably in much the larger proportion. 



Without denying the propriety of directing two processes for 

 obtaining what I must consider as really and essentially nitric 

 F acid, I think the utility of the present directions is more than 

 " questionable. Dr. Wollaston has shown that, to obtain the 



whole of the acid from nitre in the state of greatest concentra- 

 tion, it is requisite to employ two portions or atoms of sulphuric 

 acid with one of nitre. If, however, as I have observed in my 

 remarks upon the London Pharmacopoeia, one portion only of 

 sulphuric acid be employed, that portion of nitric acid, which 

 would otherwise be lost, may be condensed by passing through 

 water. 



Considering Dr. WoUaston's statement, and my own on expe- 

 riments on the subject, I am of opinion that nitric acid ought to 

 be prepared either by the use of one atom of sulphuric acid, or 

 two atoms. The Edinburgh College have steered exactly 

 between these points; but their reason for so doing, I confess, is 

 not to me at all evident. 



I put into a retort 24 parts of nitre and 16 of sulphuric acid, 

 ' and carried on the distillation as long as nitricacid was produced. 



