26 



Biological Chemistry. 



held firmly bound to the substance, the latter must be 



heated in vacua in the presence of absorbing material 



to effect complete elimination of the solvent. Whatever 

 treatment is adopted, it is neces- 

 sary that it should be continued 

 until the substance no longer loses 

 weight. 



Illustrations are appended of 

 three types of apparatus which 

 are usually employed for eliminat- 

 ing the solvent. The first of these 

 (Fig. 6) is the so-called Victor 

 Meyer bath, a double-walled vessel, 

 containing in the outer jacket a 

 liquid of known boiling point, 

 which is kept in a state of con- 

 stant ebullition, and is condensed 

 in a tube (either jacketed with 

 water or not, according to the 

 Fi 6 boiling point of the liquid used 



and the length of the tube) fitting 



into the outer jacket. The inside of the vessel is thereby 



kept at constant temperature. For elimi- 

 nating water from a substance, toluene 



(boiling point about 110) is usually 



employed. 



The second form of apparatus (Fig. 7) 



is the ordinary vacuum " desiccator," which 



is generally evacuated by connecting with 



a Bunsen water pump and manometer to 



ascertain the pressure. The lower part 



of the apparatus is filled with a liquid to 



absorb the vapour of the solvent. 



The third form of apparatus (Fig. 8) is devised for elimi- 



