34 
SELECTED ARTICLES. 
this salt forms the sulphate of lime, and this with the portion 
of lime not acted on, falls to the bottom of the kettle, while 
the potash resulting from the decomposition of the sulphate, 
enters into other combinations. The lime rapidly absorbing 
carbonic acid from the air, is converted into carbonate of lime, 
and hence carbonate and sulphate of lime constitute the largest 
proportion of the insoluble matters, which are often found in 
such large quantity in our samples of potash. 
I have been the more particular upon this point because, in 
the original specification of the patent now under considera- 
tion, it was proposed to add lime to the lixivium, a practice 
which, however general it may be, I have uniformly con- 
demned. But I have the depositions of two manufacturers, 
and the assurances of several others, that more recently, the 
mode adopted is that which I have given above, and in which 
it will be observed that such addition is omitted. 
Addition of Common Salt. — The addition of this sub- 
stance to the lixivium is a most unwarrantable practice, as it 
injures the quality of the potash, while its presence cannot 
easily be detected. The reason of this will be apparent, from 
the fact long known to chemists, that when common salt is 
added to carbonate of potash in solution, a double decomposi- 
tion takes place, the result of which is the formation of chlo- 
ride of potassium and carbonate of soda; the former being 
almost wholly useless, and the latter being employed for pur- 
poses, other than those to which common potash is ordinarily 
applied. 
The danger attending the adulteration is, that the chloride 
of potassium and carbonate of soda thus formed, are both 
highly soluble in water, so that they would escape detection 
by the ordinary mode of inspection, and samples in which 
they were contained in considerable quantity, be branded as 
" first sort." 
The reason advanced by the manufacturers in favour of the 
use of salt, is that it facilitates the " melting of the potash." 
But this advantage can by no means make up for the positive 
injury done to the potash by its addition. 
