1821 «] The Edinburgh Pharmacopma, 68 



Even however, when more mercury is used than the aoid can 

 dissolve, a large portion of peroxide of mercury is formed, which 

 may be thrown down by an alkali after the precipitation of the 

 calomel, I found that 48 parts of mercury gave 15 of- peroxide 

 after the calomel had been formed and separated. 



Oxidum Hydrargyii Cinereum. — Two hundred and forty parts 

 of calomel are directed to be decomposed by as much lime- 

 water as contains about 180 parts of lime. Now the muriatic 

 acid yielded by the calomel employed cannot combine with 

 more than 30 parts ofhme : 1 do not mean to say, if lime-water 

 be used, that an excess is of no importance ; but I think that in 

 the quantity used, a portion must during ebuUition be converted 

 into carbonate, and mix with Lie oxide of mercury obtained. It 

 seems to me that potash is i much better alkali than lime for 

 this purpose ; being so readily soluble in water, a amall quantity 

 of the solution is sufficient. 



Oxidum Hi/drargyn Rubrurn per Acidum Nitricum, — This 

 substance, to which so intolerably long a name has been given, 

 is prepared by first dissolving three parts of mercury in four 

 of dilute nitrous acid. As 1 have already noticed that mercury 

 is soluble in its own weight of this acid, and that some peroxide 

 is formed ; it appears, therefore, that one-fourth more acid is 

 now ordered than is necessary. The decomposition of that 

 nitric acid which holds protoxide of mercury in solution is suffi- 

 cient at a high temperature to convert it into peroxide. 



Subsulphm Hydtargyii Flavus is formed by boiling together 

 two parts of mercury and three of sulphuric acid. In preparing 

 corrosive sublimate, the proportions are two of metal to two and 

 a half of acid. In one case the acid must be redundant, or in 

 the other, deficient. 



Acetas Plumbi. — Prepared by dissolving white oxide of lead 

 in distilled vinegar. By white oxide of lead is meant, I suppose, 

 carbonate of lead, no white oxide existing, or being mentioned 

 among the materia medica. Litharge is the oxide usually 

 employed by the manufacturers of sugar of lead. 



It is of little importance to notice this preparation, because, 

 while it can be bought, prepared as it now is in purity on the 

 large scale, it will always be preferred on account of its 

 cheapness. 



In concluding these observations, I wish to remark, that 

 although I have scarcely mentioned any processes of this work 

 with approbation, it is not because I have found them unworthy 

 of it : on the contrary, there are many parts which I can recom- 

 mend with the greatest confidence to those who may in future 

 undertake the pffice of reforming a Pharmacopoeia. 



