so 
PURIFICATION OF SULPHURIC ACID. 
furnace, furnished with a dome ; without this precaution, 
the distillation would proceed very slowly, although the 
ebullition might be very brisk, because the vapour of sul- 
phuric acid being very heavy, and only existing at a high 
temperature, would condense before reaching the neck of 
the retort. 
This process, which is very simple, is especially advan- 
tageous, since it may be applied to the distillation of many 
otlier liquids. In fact, the substance employed to facilitate 
the ebullition, is unalterable by nearly all chemical agents, 
and for the last three of four years, since I have discovered 
it, I have employed it in nearly all my distillations. 
2. In the process just described, the quarzite acts by its 
numerous rough surfaces in facilitating the formation of the 
vapour; but theory shows that the same result might be 
obtained, that is, the distillation without bumping, if the 
acid could be made a good, or at least a better conductor of 
heat; and this point I think may be thus arrived at : — 
Sulphate of potash, and dry sulphate of soda dissolve 
readily in sulphuric acid, especially when aided by a gentle 
heat. This solution appears to conduct heat very well, and 
boils without bumping, provided there be not too great a 
quantity of sulphuric acid in proportion to the sulphate. I 
proceed thus : — I put into a retort the sulphuric acid which 
I wish to distil, and add to it from 150 to 200 grammes of 
sulphate of potash or soda for every killogramme of acid 
(from two to three ounces to the pound avoirdupois) and 
then distil as already stated. I collect two-thirds or three- 
fourths at most of the acid, and if I wish more, I add fresh 
acid, and recommence the distillation. When the process 
is terminated, I allow the retort to cool, and stop it up to be 
kept for subsequent use. I have said that I do not collect 
more than three-fourths of the acid originally put into the 
retort, and for these reasons :— In the first place, the mixture 
boils at a higher temperature than the boiling point of sul- 
