1821.] of the Edinburgh FharnKicopaia. 193 



College orders a slight excess of acid. Allow me, therefore, to 

 inform you, that when a solution of the nitrate of mercury with- 

 out excess is poured into a solution of the acetate of potassa, a 

 turbidity and deposition of subnitrate of mercury commonly 

 take place ; and the proper product is injured, unless the liquor 

 be immediately filtered as the Dublin College directs. The slight 

 excess of acid completely guards against this occurrence. 



The quantity of water directed by the Pharmacopoeia is not, 

 as you allege, too large ; it is required to keep the acetate of 

 mercury in solution at the moment of its formation, and thus 

 secures its perfect crystallization. 



Murias Hydrargi/ri Corrosivus. — The fault which you have 

 stated to the direction for this substance is the excess of the 

 common salt ; but you are certainly in a mistake in asserting 

 that it is totally useless. Here I am persuaded it is particvdarly 

 required that no portion of the sulphate may suffer the subliming 

 temperature free from the contact of muriate of soda. 



Submurias Hydrargyri PrcEcipiiatus. — Since you admit the 

 assigned proportions of acid and mercury to be correct, little 

 comment on your remark is required. The College, however, is 

 not inconsistent, as you assert, in ordering some excess of nitric 

 acid for the acetate, and forbidding it for this preparation ; 

 because the excess is advantageous for the one, and prejudicial 

 for the other. 



Oxidum Hydrargyri Cinereum. — As you have already acknow- 

 ledged with much candour, in p. 144 of No. II. of the New 

 Series of the Annals^ that you had committed an error in greatly 

 overrating the quantity of earth in the solution of lime, and have 

 in consequence withdrawn your objection to the formula for this 

 substance, it is unnecessary for me to say any thing in its 

 defence. 



Oxidum Hydrargyri Rubritm per Acidum Nitricum. — If the 

 diluted nitric acid have been formed from the strongest acid, 

 you are perfectly correct in saying Ihat it will dissolve an equal 

 weight of mercury, and in that case more acid is ordered by the 

 Edinburgh College than is necessary for preparing this substance. 

 But if the best acid usually met with in apothecaries' shops be 

 employed, in consequence of its inferior strength, the proportion 

 assigned in the Pharmacopoeia will be found most suitable. 



Acetas Plumhi. — In the formula for this substance 1 acknow- 

 ledge that you have detected an oversight on the part of the 

 College. I trust, however, it is a very venial one, as it consists 

 merely in employing the older instead of the new name for the 

 oxide of lead used in this preparation. 



I have now gone through the different articles of your criticism, 

 and with the exception of the trivial oversight in nomenclature 

 now admitted, I trust that every chemist who shall peruse these 

 remarks will be satisfied that none of your objections are well 

 founded. I am very far from thinking that our Pharmacopoeia 



ISlew Series, vol. i. n 



