ADULTERATION OF POTASSA BY SODA. 207 
But even when it is wished summarily to determine pre- 
viously the quantity of accidental impurities of potassa, 
to subtract them from 100 grains of potassa, and to reduce 
to 100 the number obtained after the neutralisation, an 
accurate result cannot be arrived at, because we rarely find 
in commerce a potassa which contains only simple carbo- 
nate of potassa, without any mixture of free caustic potassa, 
or, which is most common, of sesquicarbonate of potassa, 
and in both these cases the numbers indicated in the Table 
would be inaccurate ; for if a pure potassa, submitted to 
examination, contained free caustic potassa, we should, 
from the employment of the test-acid, maintain, according 
to the foregoing Table, that this potassa contained soda, 
whilst at another time we should declare to be free from 
adulteration a potassa containing much sesquicarbonate of 
potassa, and which would not be mixed with too great a 
quantity of soda. It is evident, therefore, that this Table 
would be applicable only after having first not only removed 
from the potassa submitted to examination all the foreign 
mixtures, with the exception of soda, but also after having 
transformed into simple carbonate the alkali obtained, if 
this were potassa alone, or mixed with soda ; but as this 
operation would be too difficult, and would require too 
much chemical skill, this mode of testing, to ascertain the 
proportion of soda contained in potassa, cannot be admitted, 
at least as an ordinary process. 
The same observation is applicable to the case in which 
it is desired to calculate the proportion of soda contained in 
a potassa by the increase of weight which takes place 
when moistened potassa is exposed to an atmosphere of 
carbonic acid until there is no further augmentation of 
weight, or by the loss of weight produced by the expulsion 
of carbonic acid by potassa by a more energetic acid ; in- 
deed, these two processes could be used only for operating 
on mixtures of pure simple carbonate of potassa with anhy- 
drous simple carbonate of soda. 
