Detection of Adulterations. 81 



of lead, and powdered brick. Such frauds, however, are easily de- 

 tected by heating to low redness a portion of the oxide ; by which 

 process the mercury and the oxygen are separated and volatilized, 

 while the other substances remain fixed at that temperature. Should 

 vegetable matter have been added to the oxide, the latter will afford 

 carbonic acid when heated ; or, if mixed with water, the oxide 

 will sink rapidly, while the vegetable matter will float for a longer 

 time. As the red precipitate of commerce is prepared by cautiously 

 heating the nitrate of mercury, it almost always contains a portion of 

 undecomposed nitrate from which it should be freed, by exposure to 

 a heat gradually increased until it ceases to evolve nitrous vapors, and 

 gives off good oxygen. 



Peruvian Bark. — The physical characters of the various species 

 met with in commerce, being detailed by authors easily accessible 

 to our readers, we shall dwell rather upon the chemical researches 

 connected with the subject.* The external appearances not being 

 always satisfactory, it sometimes becomes necessary to resort to chem- 

 ical analysis, to determine the quantity of quinine contained in the 

 bark, and its consequent value as a medicine. M. Tilloy recom- 

 mends the following process ; add one ounce of the bark in coarse 

 powder, to twelve ounces of alcohol sp. gr. '867, and at the tem- 

 perature of 120°. After digesting for half an hour, decant the al- 

 cohol, and repeat the process ; observing to press the bark after de- 

 canting the second portion. Mix the several portions of alcohol, fil- 

 ter and add a solution of bi-acetate of lead as long as a precipitate 

 falls. Then filter the solution, which contains acetate of quinine, 

 and add cautiously sulphuric acid, as long as a white precipitate 

 falls. This precipitate is sulphate of lead ; and does not occur at 

 all, unless a slight excess of the bi-acetate has been used in the for- 

 mer part of the process. When the sulphate of lead ceases to fall, 

 add a litde more sulphuric acid, in order to convert the acetate of 

 quinine into a sulphate. Then filter and distil. f We thus obtain 

 sulphate of quinine and a fatty matter which adheres to the sides of 

 the vessel. Decant, and add just enough ammonia to precipitate 

 the whole of the quinine. Wash the precipitate with warm water, 

 and dissolve it in very dilute sulphuric acid containing an admixture 

 of animal charcoal ; by which means we shall obtain, on the first 



* See observations and experiments on Peruvian Bark, by G. W. Carpenter, Vol. 

 XVI, p. 28 of this Journal, 

 t It should be stated how far the distillation is to be carried. 



Vol, X1X,--No. 1. 11 



