246 



EVAPORATION. 



[CH. IX 



has drained away the felt-like layer of asbestos can be 

 pressed with a pestle to any degree of tightness required. 

 The asbestos and paper can be washed and used again. 



Evaporation of solutions. 



Much time is always necessary for this tedious opera- 

 tion, but work can generally be so arranged that it can go 

 on whilst other experiments are in progress. 



Evaporations should always be conducted on the water- 

 bath, but even so a considerable amount of 'charring' 

 usually occurs, and this discoloration of the solutions, 

 not being easily removable, renders the subsequent exami- 

 nation much more difficult. 



By concentrating solutions under reduced pressure the 

 difficulty is largely avoided. By the use of a good water 

 filter-pump aqueous solutions can be concentrated fairly 

 rapidly at 50° — 60° C. and alcohol can be distilled off below 

 50° C. 



Fig. 45. 



A convenient form of apparatus for distilling off liquids 



