42 
SELECTED ARTICLES. 
of those chemical principles, which should regulate the manu- 
facture. But this desirable result can scarcely be expected, 
without some improvement in the mode of inspection. I am 
aware of the tact which the inspectors acquire, by the con- 
stant examination of samples of potash, and of the accuracy 
with which they ordinarily judge of their relative purity. 
But there are cases in which they are liable to be deceived 
and against which, it is important to guard. Being sensible 
of the extreme difficulty of introducing new regulations into 
such an every day business, it is not without some hesitation, 
that I am induced to offer the following suggestions. 
1. There are now, I believe, three sorts of potash recog- 
nised by the inspectors ; but if my information be correct, the 
samples passed as " first sort," always contain a considerable 
proportion of lime, to say nothing of soluble impurities. 
Another brand designated " pure," or by any other conve- 
nient term might, in my opinion, be advantageously intro- 
duced. Samples thus branded, should contain no lime or 
salt, and at least eighty-five per cent, of carbonated potash. 
2. The insoluble impurities may be easily determined, by 
dissolving a known quantity of potash, as five hundred or one 
thousand grains, in pure rain water, conducting the operation 
in a glass flask, and applying a gentle heat to facilitate the 
solution. Then filtering the solution, washing the precipitate, 
if any, and drying it carefully, the per centage of insoluble 
matter can at once be ascertained. When the proportion 
exceeds two or three parts in the hundred, it is probably due 
to the carelessness of the manufacturer, or to the addition of 
lime to the alkaline liquor during its evaporation. 
3. The soluble impurities are more difficult of detection; 
and it is by no means easy to reduce the process to a single 
trial. The mode ordinarily prescribed in chemical works, 
consists in determining the saturating power of the specimen 
under examination, and very convenient instruments for this 
purpose are described by Mr. Faraday, and MM. Descroizilles 
and Gay Lussac. In these instruments sulphuric acid of 
known specific gravity, is employed in a fixed quantity, and 
