1824.] Pharmacopoeia Londinensis. 455 



sesses, and to which its solvent power is owing. The quantity 

 of iron directed to be used appears to me to be almost exactly 

 such as, if it were all dissolved, would render the medicine of such 

 a degree of strength, as I found it actually to possess when pre- 

 pared with sherry wine ; namely, 22 grains of peroxide of iron in 

 a pint ; the College order 60 grains of iron to be converted into 

 tartarized iron, and the compound formed to be dissolved in 60 

 ounces of dilute spirit ; and as 60 grains of iron are convertible 

 into about 85 grains of peroxide, and as 60 ounces would contain 

 this quantity, a pint, or 16 ounces, would hold about 22*6 grains 

 in solution. 



Jt happens, however, unfortunately, that three causes conspire 

 to prevent this medicine from possessing the strength of the 

 former ; first, the whole of the iron is not dissolved by the super- 

 tartrate of potash ; secondly, apart of that which is dissolved is 

 rendered insoluble by the process of drying ; and lastly, a portion 

 of what the water dissolves is immediately precipitated by the 

 spirit, and the quantity is so very considerable that the vinum 

 ferri now contains only 16 grains of peroxide in a pint instead of 

 22 as formerly. In this preparation" therefore, merely for want 

 of experiment, and by taking that for granted which did not 

 happen to be true, the strength has been reduced to about two- 

 thirds that which it formerly possessed, and no notice what- 

 ever is of course taken of the change. 



In preparing calomel, the College have introduced what 

 is certainly a very considerable improvement ; namely, form- 

 ing it by one sublimation, instead of first preparing corrosive 

 sublimate, and then triturating that with an additional portion of 

 mercury, and subliming again ; the present process consists in 

 mixing bipersulphate of mercury with mercury and common 

 salt, and subjecting the mixture to sublimation; the sublimed 

 calomel is then to be reduced to powder, and washed with a 

 solution of muriate of ammonia, in order, I presume, the more 

 readily to dissolve any corrosive sublimate which may have been 

 formed ; this, perhaps, might have been spared, for corrosive 

 sublimate is sufficiently soluble in water to admit of its sepa- 

 ration from calomel during the process of elutriation. If, 

 however, no corrosive sublimate be actually found with the ca- 

 lomel, the manufacturer may use the same solution of muriate 

 of ammonia repeatedly, and if, on the other hand, any be dis- 

 solved, it may be converted into hydrargyrum pra:cipitatum 

 album. 



In comparing, however, the processes for procuring corrosive 

 sublimate and calomel, a strange disregard of proportions has 

 occurred ; in order to convert 24 parts of mercury into corrosive 

 sublimate, the College direct the use of 30 parts of sulphuric acid 

 and 48 of common salt; while in preparing calomel, 48 parts of 

 mercury are to be treated with 30 ounces of sulphuric acid, and 

 only 18 of common salt. Now it must be granted upon any 



