Dehydrating and Clearing 103 



bottle at a time, to keep a layer of some good dehydrating agent at the 

 bottom of the bottle. The best dehydrant for use in absolute alcohol is 

 anhydrous copper sulfate, for this not only absorbs water readily but also 

 indicates, by changing from white to blue, when it is becoming ex- 

 hausted. Anhydrous calcium sulfate, in the form commercially known as 

 Drierite, is a somewhat better dehydrating agent but cannot be used 

 as an indicator in alcohol. 



One may also anticipate that both the hydrocarbons and the essential 

 oils used for clearing will be in a water-saturated condition when pur- 

 chased. These, therefore, should always be dehydrated as soon as they 

 have been purchased— preferably using Drierite— but, since they have 

 little tendency to absorb moisture from the air, it is not necessary to keep 

 them in bottles containing a dehydrating agent. 



