238 Mr. Murdoch o»* the Impurity of some Drugs. 



composition of the sulphur = sulphur 49*27, and sulphata of lime 50-73. 

 But as the gypsum was in crystals, it obviously contained its water of 

 crystallization, which must therefore be calculated. The constituents 

 of hydrous gypsum are:— Ca =35, SO3 = 5,2 HO = 225 = 10-75. 

 The quantity of water belonging to the sulphate of lime found in 

 the analysis will therefore be 13'42 per cent. The true constituents 

 then are : — 



Sulphate of lime, .... 50'73 

 Water of crystallization, . . . 13"42 



Sulphur, 35-85 



100- 



3. OXIDE OF ZINC. 



This oxide generally effervesces on the addition of an acid, proving 

 the presence of carbonate of zinc, or of the carbonate with which it 

 has been precipitated. When to the solution of this oxide in muriatic 

 acid an excess of caustic ammonia is added, some brownish red flocks 

 of peroxide of iron remain undissolved, (containing perhaps a little 

 alumina,) amounting to about li per cent. 



4. RED OXIDE OF IRON. 



This oxide, as sold in the shops, has been examined by my brother, 

 Mr. James Murdoch, and found to contain a small per centage of 

 alumina. 



5. TARTAR EMETIC 



This salt generally contains a small quantity of peroxide of iron. 



Note. — The first person who published an account of the extraordi- 

 nary mixture called calamine in the shops, was Mr. Brett, in 1837, in 

 the British Annals of Medicine, vol. i. p, 485. He found, however, 

 traces of lead and zinc in the specimen which he analyzed — a circum- 

 stance which has never occurred to me either before or since that period. 

 It is possible, therefore, that the specimens may vary slightly. Sul- 

 phate of lead is a probable ingredient in minute quantities, but there 

 is much reason to doubt if the manufacturer of this article is honest 

 enough to supply his customers with even a trace of zinc. It is not 

 a little remarkable that this adulterated article should have for so 

 long a period been infesting every drug shop, to the utter exclusion, 

 apparently, of the genuine article in England and Scotland, without 

 any complaint from those who purchase it. Does this fact not prove 

 that as calamine is used in the form of ointment, it is the lard which 

 is the efficient application? Mr. George Schweitzer, of Brighton, first 

 published an account of the impure milk of sulphur, in the British 

 Annals of Medicine, in 1837, vol. i., p. 618., and showed that the sul- 



