192 HYPOSULPHITE AND TRITHIONATE OF POTASH. 
some degree explains the formation of S 3 O 5 KO by M. 
Langlois's process. In fact, it may be admitted that the 
sulphur, on dissolving in the bisulphite of potash, forms 
hyposulphite ; and that the excess of sulphurous acid, in- 
stead of being disengaged, reacts upon this salt so as to 
produce the trithionate. This supposition, in fact, led me 
to examine the action of sulphurous acid on the hyposul- 
phite of potash. 
The following is the method I employ for the preparation 
of M. Langlois's salt: — 
I procure a solution of hyposulphite of potash, so con- 
centrated that it will not mix with alcohol of 0.851 spec, 
grav. When dry or crystallized hyposulphite of potash is 
conveyed into water to which about g volume of this alco- 
hol has been added, the alcohol separates at a certain pe- 
riod, and comes to the surface, I add then no more salt, 
and pass through some sulphurous acid, generated from 
sulphuric acid and powdered charcoal; the solution of 
the hyposulphite is, however, previously heated to about 
77° or 86°. If the disengagement of the gas is rather rapid, 
this temperature maintains itself. From time to time a 
little hyposulphite is added, taking care that the tempera- 
ture always remains constant. When the liquid acquires 
an intense yellow color, and gives off the smell of sulphu- 
rous acid, the disengagement of this gas is discontinued, 
and after some hours, in the course of the night, the liquor 
becomes colorless, quite loses the odor of sulphurous acid, 
and deposits a large quantity of crystals. The alcohol 
which floated on the surface now mixes with the liquid, 
which indicates that a fresh quantity of hyposulphite should 
be added, and more sulphurous acid passed through, if a 
greater quantity of crystals is desired- 
When a sufficient quantity of these crystals has been ob- 
tained, they are dissolved in water at 122° or 140°, the so- 
lution filtered to separate the sulphur they contain, and then 
an eighth of its volume of alcohol of 0.851 spec. grav. added 
