10 Original Communications. 
failed, on account of the difficulty of separating the iron 
with which it is impregnated. If they had been acquainted 
with the simple process just mentioned, I have no hesitation 
in saying that they would have succeeded. 
ADULTERATIONS OF CALCINED MAGNESIA. 
Magnesia is commonly adulterated with Jlour, chalk, lime 
and gypsum. 
Flour may be detected by its burning when thrown upon 
red hot iron or coals ; or its presence may be proved by add- 
ing to the specimen an aqueous solution of iodine, when if it 
contain flour a blue compound will be formed. 
Chalk, by dissolving it in nitric acid, and precipitating with 
sub-carbonate of ammonia. 
Lime may be detected by dissolving it in dilute sulphuric 
acid, and precipitating with oxalate of ammonia. 
Gypsum may be discovered by boiling the suspected mag- 
nesia in distilled water, and adding oxalate of ammonia, 
which will precipitate oxalate of lime ; or by adding muriate 
of barytes, we will have a precipitate of sulphate of barytes. 
I have ascertained by experiments that mixtures contain- 
ing magnesia, adulterated with calcined sulphate of lime, 
after standing short time, will become solid. The circum- 
stance which led to these experiments was an article by an 
apothecary, in the twelfth number of the Journal of the Phila- 
delphia College of Pharmacy, vol. iii. p. 290. 
At the time this communication appeared, it gave rise to 
some speculations amongst some of the members of this Col- 
lege, and we, with the Philadelphia apothecary* were unable 
to account for the " singular change," and a number of ex- 
periments were instituted by Professor Rogers, Mr. Geo. D. 
Coggeshall and myself, with the view of ascertaining the 
cause of the phenomenon. We prepared the mixture ac- 
cording to the above formula, and also varied the ingre- 
dients in every variety of proportion, but a permanently thin 
mixture was uniformly the result. 
