HYPOSULPHITE AND TRITHIONATE OF POTASH. 191 
I will describe in a few words the process which I have 
adopted for preparing the hyposulphite of potash from the 
neutral sulphite. It may be of some service, as pure hy- 
posulphite of soda may equally be obtained by it 5 and this 
is now a very important object of commerce. 
Bisulphate of potash is prepared as above described ; the 
carbonate of potash is wholly converted into bisulphite 
when the sulphurous acid passes off without dissolving. 
This is then converted into the neutral salt by adding car- 
bonate of potash until it produces no further effervescence ; 
the neutral sulphite, thus prepared, is boiled in a capsule or 
flask with flowers of sulphur, for fifteen or twenty minutes, 
stirring frequently with a glass rod to facilitate the solution 
of the sulphur. The liquid separated from the excess of 
sulphur is evaporated over the fire to a syrupy consistence • 
if any sulphate has formed in the course of the operation by 
the absorption of oxygen, a portion of the salt separates at 
this point of concentration. The clear liquid is decanted 
after 24 hours' standing, and again concentrated, which 
however does not determine the precipitation of a fresh 
quantity of sulphate, and in the course of 24 hours beauti- 
ful crystals of hyposulphite gradually form in a dry place. 
The presence of the sulphate, far from being disadvan- 
tageous, causes the hyposulphite to crystallize better than 
from a pure concentrated solution. The crystals as ob- 
tained are perfectly colorless, transparent and hard, very so- 
luble in water, not deliquescent, and contain 2 equiv. water 
of crystallization. 
The hyposulphite of soda may be purified by melting it 
in its water of crystallization ; on cooling, very beautiful 
crystals of hyposulphite separate, which are removed from 
the liquid containing the impurities. 
I will now proceed to describe the process I employ for 
preparing the trithionate of potash. 
I obtain this salt by the action of sulphurous acid on the 
hyposulphite of potash. This very remarkable action in 
