( 278 ) 



Description of an Apparatus Jbr Evaporating Fluids, and also 

 for separating Salts Jrorn their aqueous solution by Crystalli- 

 zation without the aid of the Air-pump. By P. A. Von 

 BoNSDORF, Professor of Chemistry in the Alexander Univer- 

 sity in Finland. 



W HEN we wish to evaporate gradually the water of a solution, 

 and particularly to dry such matters as will not bear exposure 

 to heat without being decomposed or otherwise changed, we 

 employ, as is well known, free or rarified air, in which the aque- 

 ous vapour as it rises is removed by substances, particularly 

 sulphuric acid, that greedily absorb moisture. But, as the air- 

 pump, the instrument employed for obtaining a vacuum, is not 

 in the possession of every one, and besides it is difficult to pro- 

 cure one in which the bell-glass will remain long in the state of 

 a vacuum, and even the best is so far inconvenient, that in it 

 only a small number of evaporations can go on at the same 

 time, the account of another method for evaporating water will 

 not, we think, prove unacceptable to the friends of science. 



In a series of experiments I undertook, in the year 1826, on 

 the salts which are formed by the union of the chloride of elec- 

 tro-negative and electro-positive metals, I procured a number 

 of salts, which (as they could only be prepared in small quan- 

 tities), it was nearly impossible to obtain well crystallized, parti- 

 cularly when they had a tendency to deliquesce. I found my- 

 self, therefore, arrested in the midst of my investigations, because 

 one air-pump only was at my command. This difficulty in- 

 duced me to think of other means. It appeared to me that air 

 has little or no effect in retarding evaporation, providing it is 

 kept dry or nearly so ; that is, if the aqueous vapour is absorbed 

 by an appropriate substance as fast as formed. I therefore 

 tried whether or not a saline solution, placed under a bell-glass, 

 in which there was at the same time a saucer with sulphuric 

 acid, could be evaporated to crystallization, and actually found 

 that, by this arrangement, my object was gained, notwithstand- 

 ing the pressure of the atmosphere. 



The following is a description of the apparatus I used for 

 this purpose. 



