State Board of Pharmacy Questions on Chemistry

Abstract

and Belgian Pharmacopeias define quantities less than 1 mg. as unweighable, the Swiss and Danish Pharmacopaeias quantities of 0.5 mg. and less. Crucibles or dishes of platinum are usually preferable to porcelain for exact determinations af non-volatile and non-combustible matter, on account of better heat conduction and because of reaction of some ash constituents with silicates at high temperatures, with a consequent loss in weight of the residues. For quantities of 0.1 to 0.2 gm., platinum crucible lids are generally best suited. The German Pharmacopaeia give the following directions for ash determinations: A suitable quantity is first carbonized in a crucible at a low temperature, then incinerated. T o hasten combustion of the carbon, the flame is removed from the crucible occasionally for a short time. If complete incineration cannot be attained by a moderate heat, the mass is mixed with hot water and transferred to a filter of known ash content. The filter and contents are washed with a little, water, then returaed to the crucible, dried and incinerated. After cooling, the filtrate and washings are added and evaporated on a water-bath after addition of a little ammonium carbonate. The residue is heated to dull redness, cooled, weighed, and filter ash subtracted.