293 



the analysis with alcohol the whole of them is dissolved, while by 

 commencing with ether a separation of two different groups is 

 effected at the outset. 



3. Not less advantageous is the previous treatment with ether 

 and then with alcohol for the subsequent one with water, whereas, 

 if the commencement be made with water, inconveniences of 

 various kinds are incurred. Amongst these stand out in the first 

 line the difficulty of filtering, caused sometimes, it is true, by a 

 considerable amoimt of gum, but also and often alone by finely 

 susj)ended particles of resins and fats. These could, indeed, easily 

 be removed by a few drops of dissolved acetate of lead, but this 

 would disturb the course of the analysis by introducing acetic acid 

 and by otherwise complicating the process. Since the water is to 

 be employed not only cold but also hot, fats and resins present 

 would be liable to undergo alterations, and greater still would be 

 the difiiculty with amylaceous substances, since the formation of a 

 paste would make straining impossible, and to overcome this diffi- 

 culty by means of adding an acid, in order to convert the paste of 

 starch into sugar, would involve troubles of another kind, for in- 

 stance, the breaking up of glucosids or resins, or the displacement of 

 volatile acids. 



Before commencing the analysis the question must be answered, 

 how much of the material has to be worked upon, and how much may 

 be available. If it consists of whole herbs or of parts of these as 

 roots, barks, leaves, flowers or seeds, no more than 100 grammes 

 of the substance should be employed, even if there be no scarcity 

 of material. With very costly or not easily procurable substances 

 a less amount must suffice, and with gummous or resinous exuda- 

 tions or with excretions of other kind it is possible to operate even 

 upon 20 grammes, since the number of constituents of these 

 bodies is comparatively small. 



After the analysis, completed according to I. to VII., has given a 

 clear idea of the chemical constitution of the substance under in- 

 vestigation, then those constituents which have been obtained in 

 too small a quantity for a thorough investigation, such as alkaloids, 

 bitter substances, volatile oils, volatile acids, must be prepared 

 from considerably larger quantities of the raw material, according 

 to the methods indicated under VIII. to X. 



I. — Quantitative Estimation of the Water. 



Weigh off from the substance in the possibly finest state of com- 

 minution 2 to 5 grammes, according to its bulk, into a platinum 

 crucible, the weight of which and of its lid having been before 

 carefully determined ; place the crucible uncovered into a metallic 

 air-bath furnished with a centigi'ade thermometer, put the whole 



