236 Mr. Murdoch on the Impurity of some Drugs. 



about equal to that obtained bj means of the same apparatus, from a 

 solution of sugar in water, containing five grains to the ounce. Should 

 farther observations confirm tho idea here suggested of the existence 

 of sugar in the blood as a normal product, it is obvious that a corre- 

 sponding modification must be made of the prevailing theories of 

 diabetes, according to which the production of sugar is regarded, as 

 the essential derangement of action in which that disease consists. 



27th Marchy 1844, — The President in the Chair. 



A Report from the Botanical Section was read, stating that at their 

 meeting on the 25th instant, Mr. Henrj Craig had presented seeds 

 from Pernambuco ; and Mr. Balloch read a paper on two disputed 

 species of fungi found on oak leaves — one of the species being known 

 as oak spangles — which some authors consider to be caused bj insects, 

 but which he maintained to be true fungi. Drawings were exhibited 

 illustrative of their high organization. 



The following communication was then read. 



LI. — On the Impurity of some Drugs. By Mr. David Murdoch. 



1. CALAMINE, OR CARBONATE OF ZINC. 



As the calamine or impure carbonate of zinc sold in London, had 

 been frequently examined by Dr. R. D. Thomson, and found always 

 destitute of zinc, it became a matter of some interest to ascertain if 

 the same remark applied to the calamine which occurs in commerce 

 in Glasgow. Accordingly, at the request of Dr. Thomson, a specimen 

 was subjected to analysis. The colour of this substance is well known 

 to be a light red. When it is boiled with muriatic acid it effervesces 

 slightly, and becomes perfectly white, the residue, consisting of a heavy 

 white powder, which on being heated on charcoal before the blow-pipe, 

 and then digested in acid, gives out the smell of sulphohydric acid ; or 

 when fused with carbonate of soda and digested in water, sulphate of 

 soda is dissolved and carbonate of barytes remains unacted on. The 

 main constituent of the commercial calamine is thus obviously sulphate 

 of barytes. To ascertain if any zinc was contained in the red powder, 

 the acid solution which was boiled upon it was mixed with a quantity 

 of caustic ammonia in excess, which precipitated the peroxide of iron 

 and alumina. This precipitate was filtered, and the ammouiacal liquid 

 which passed through the filter was precipitated by oxalate of am- 

 monia. The oxalate of lime was thrown on a filter, and the washings 

 evaporated to dryness and heated to low redness in a platinum capsule. 

 No residue was left, showing the absence of zinc and magnesia. 144 

 grains of calamine in one analysis gave of sulphate of barytes and some 



