118 ELEMENTS OF GENERAL SCIENCE 



does not contain the impurity, it condenses into pure water. 

 The process is called distillation. This is the most certain 

 method of securing pure water (fig. CO). 



Large distilling plants are employed to produce commercial 

 supplies of pure water for drinking purposes, for ice manu- 

 facture, and for other uses ; and in private establishments and 

 in laboratories smaller plants are sometimes maintained. 



136. Use of thermometers in candy-making. The fact that 

 sugar dissolved in water raises the boiling point has an 



FIG. 60. Distillation 



The solution to be distilled is placed in A ; the steam which passes through the 

 tuhe is condensed in B, which may he cooled with ice or snow 



interesting application in candy -making. The temperature at 

 which the sirup boils depends upon the amount of sugar 

 used. If we know from experience at what temperature to 

 stop the boiling to get candy of the desired texture, we can 

 get much more certain results by always using a thermometer. 

 Temperatures at which boiling should stop are as follows : 



