ON SESQUICARBONATE OP SODA. 143 
ART. XXXIV. — ON THE FORMATION AND COMPOSITION 
OF SESQUICARBONATE OF SODA.* 
BY HERMANN. 
The former opinion, that the sesquicarbonate of soda is 
formed by the ebullition of solutions of bicarbonate of soda, 
which should then allow half an equivalent of carbonic acid 
to be disengaged, has already been refuted by Rose. That 
chemist has found that the solutions of bicarbonate of soda 
completely disengage their second atom of carbonic acid by 
exposure in vacuo, or by long boiling. He has not suc- 
ceeded in obtaining crystals of sesquicarbonate of soda with 
solutions composed of equal atoms of bicarbonate and simple 
carbonate of that base. 
The conditions in which the sesquicarbonate of soda is 
formed were hitherto unknown. Hermann thinks he has 
found them. This salt is not produced by crystallisation in 
aqueous solutions; it is then decomposed into bicarbonate 
and carbonate of soda, which crystallise separately; but it is 
very easily formed, according to this chemist, by efflores- 
cence. 
If, then, we promptly combine by the boiling, concen- 
trated solutions of bicarbonate of soda, and if we thus pre- 
vent the second atom of carbonic acid from being com- 
pletely disengaged; if we fuse together equal atoms of bi- 
carbonate and simple crystallised carbonate of soda, in the 
water of crystallisation of the latter, and if the mass be 
dried; finally, if bicarbonate of soda be heated to a tem- 
perature not exceeding 200° C, saline masses are obtained, 
which consist chiefly of sesquicarbonate of soda. To obtain 
them in the crystallised state, it is sufficient to expose them 
for some time to the action of damp air, especially in cellars. 
* Journal fur Praktische Chemie. 
