240 PREPARATION OF [CH. IX 



Among general works which may be consulted for 

 descriptions of the apparatus and manipulation used in 

 the experiments are: 



SACHSSE. Die Chemie und Physiologie der Farbstoffe, 

 Kohlenhydrate und Proteinsubstanzen. (Leipzig, 1877.) 



FRANKLAND. Agricultural Chemical Analysis. (Mac- 

 millan and Co., 1889.) 



DRAGENDORFF. Plant Analysis. (Trans, by GREENISH.) 

 (Bailliere, Tindall and Co., 1884.) 



In references to original papers the ordinary abbrevia- 

 tions are used. 



Preparation of the material to be examined. 



For extraction with benzene, ether, etc., the material 

 must be dried as completely as possible, and as the residue 

 will generally be treated with boiling alcohol before 

 extraction with cold water, the original substance may be 

 dried at 100 C. in the steam-oven, till it ceases to lose 

 weight. Fixed oils and fats, glucosides, tannins, carbo- 

 hydrates including starch, will not be seriously altered by 

 drying at 100. 



On the other hand proteids and ferments would be 

 completely changed by drying at 100, and in these cases 

 either the undried material is used or material which has 

 been dried at a temperature not exceeding 30 this is 

 commonly spoken of as air-dried material. 



Where comparative experiments only are being made it 

 is not a matter of much consequence whether the percent- 

 ages are calculated for material which is fresh, or has been 

 air-dried, or dried at 100, but if determinations of several 



