456 Analyses of Books. [June, 



theory that 24 parts of mercury will require exactly as much 

 common salt to convert them into corrosive sublimate as to 

 convert twice the weight of mercury into calomel, and yet 48 

 parts of common salt are ordered for the production of an effect 

 in one case, while an equal effect is to be produced in the other 

 by 18 parts ; the fact is, that the 48 parts are much in excess, 

 as I pointed out long since ; 49 parts of sulphuric acid cannot 

 decompose more than GO parts of common salt ; but in preparing 

 corrosive sublimate, after about 12 parts of the 30 of sulphuric 

 acid directed to be boiled with the mercury are decomposed by 

 oxidating it, the remaining 18 must be supposed capable of 

 decomposing 48 of common salt ; it is, therefore, evident that 

 about 26 out of 48 of salt are wasted. Why the quantity was 

 not diminished as to be more in agreement with the directions 

 for preparing calomel, I cannot discover. 



The preparations of lead do not call for any particular obser- 

 vation, excepting, that as the sulphate of copper, soda, and 

 potash, are introduced into the materia medica, no reason can 

 possibly exist why the acetate of lead should not also have 

 been ; it is perfectly well prepared for the purposes of 

 the arts, and the acetic acid of which it is made not being; sub- 

 ject to any duty, it may be purchased at so much cheaper a rate 

 than that at which it can be prepared, the formula is therefore 

 useless ; it may also be observed, that the acidum aceticum fortius 

 diluted with water would have answered the purpose of making 

 the liquor plumbi subacetatis. 



Oxide of zinc formerly prepared by combustion is now directed 

 to be formed by decomposing the sulphate of zinc with ammonia. 

 I have not examined the preparation ; there is a slight difficulty 

 attending the use of the caustic alkalies in precipitating oxide 

 of zinc, which is, that if accidentally added in excess, they 

 redissolve the precipitate at first formed. On this account I 

 prefer carbonate of soda or potash, which I recommended some 

 years since for this purpose. The advantage of the new mode of 

 preparation is, 1 think, considerable, as it prevents the presence 

 of any minute portions of metallic zinc which were apt to render 

 the ointment of zinc gritty. 



It appears to me that the College ought to have been more 

 consistent in their directions. I have already shown some 

 instances of their deficiency in this respect, and the spirits of 

 ammonia afford additional proofs of want of attention. In the 

 Pharmacopoeia of 1787, the spiritus ammonia? and spiritus ammo- 

 nite aromaticus are similar in strength, varying only in the 

 aromatics which the latter contained ; but in the present Phar- 

 macopoeia, and indeed in the last, as I pointed out, the 

 proportions of spirit, muriate of ammonia, and carbonate of 

 potash, are extremely different. In preparing the spiritus 

 ammonite, 32 parts of muriate of ammonia are directed to 

 be decomposed by 48 of subcarbonate of potash, a quantity 



