STARTER MAKING 



31 



a dead air space of about three inches between the 

 tin jacket and outer tank. This space surrounds the 

 entire tin jacket or inner tank, and can be filled with 

 warm air in the winter and cold in the summer, to 

 impart uniform temperature to the samples contained 

 therein. About six inches of water may be kept in 



FIG. 26 



the tank to aid in maintaining an even temperature. 

 Ice may be used in summer if obtainable. Of course 

 the opening E should be closed in the summer. The 

 accompanying cut represents the vat. E represents 

 the opening from below to the dead-air space and 

 the place for the lamp which is kept burning con- 

 tinually except when room temperature is 70 F. or 



