ADULTERATION OF POTASSA BY SODA. 205 
the perchloric acid is riot driven off under the form of gas 7 
and leaves, on the contrary, the perchlorate of potassa. The 
two perchlorates are then cautiously calcined, and they are 
converted, with a disengagement of oxygen, info chloride 
of potassium and chloride of sodium, which serve for cal- 
culating the quantities of potassa and soda. 
Although this second process is not so expensive as the 
preceding, the other objections apply to it; for not only 
does it require too much chemical skill, but it likewise gives 
an inaccurate result, since the potassa of the chloride of 
potassium, and sulphate of potassa contained in the potassa, 
is found in the result, and because it is necessary, conse- 
quently, previously to make an accurate determination of 
the impurities accidentally or purposely mixed with the 
potassa. 
All the re-agents which are now employed for defecting 
potassa and separating it from soda, such as the tartaric, 
hydrofluosilicic, and carbazotic acids and sulphate of alu- 
mina, are, more or less, liable to the objection of indicating 
not only the alkali combined with the carbonic acid, but 
also that combined with the sulphuric and hydrochloric 
acids, &c, and not being able, consequently, to give an 
accurate result without a previous and minute determina- 
tion of the accidental mixtures of potassa. 
It should, therefore, rather be possible to find, in the 
capacity of saturation of potassa and soda, a means of solv- 
ing the question ; for, by comparing the capacity of satura- 
tion of potassa with that of soda, we find a very considerable 
difference. Thus, for example, 100 grains of dry simple 
carbonate of potassa require for their neutralisation 1,000 
grains of pure dilute sulphuric acid, (for alkalimetary) 
which contains nearly 82 per cent, of anhydrous acid, 
whilst 100 grains of anhydrous carbonate of soda require 
nearly 15 per cent, of the same acid for their neutralisation. 
It would, therefore, be sufficient to establish, by calcula- 
tion, a Table in the following form for each hundredth, in 
order to be able, only after the employment^ an alkalimetric 
