68 



with 100 c.c. alcohol of 50° Tr. The filtrate is thus brought to 

 about 220 c.c. It is then carefully evaporated on a water bath to 

 about 50 c.c, refiltered, when necessary, and finally evaporated to 

 dryness in a weighed platinum dish. The drying is finished in an 

 air bath at from 100 to 110° C, and is to be continued until no 

 further loss of weight is observed. To facilitate the drying, it is 

 well to add to the solution, which has been concentrated to about 

 10 c.c, some absolute alcohol from time to time, whereby the carbo- 

 hydrates are precipitated, and then to spread the mass over the sides 

 of the dish by means of a spatule. Evaporation is thus greatly accel- 

 erated. "When constant weight has been reached, the contents of 

 the dish are incinerated, and, after deducting weight of dish and 

 ashes from the weight first determined, we obtain the weight of 

 the soluble carbohydrates. 



Determination of Insoluble Carbohydrates. 



The residue from the alcohol treatment is transferred into a 

 flask of 400 c.c contents, and then 200 c.c. of water and 20 c.c. 

 pure hydrochloric acid are added. Loosely covered with a cork, 

 the flask is inserted into the water of a boiling water bath, and 

 kept there for from three to four hours. The inversion will be 

 completed by this time. The contents of the flask are then care- 

 fully neutralized, whereby any albumen which may have gone into 

 solution under the influence of heat and acid, is precipitated. The 

 neutralized solution is then filtered through a ribbed filter, flask 

 and filter being washed until the filtrate measures 500 c.c. The 

 amount of sugar in this solution is determined by Fehling's solu- 

 tion as previously described. For the calculation of starch, 

 Sachsse's figures, 108 glucose = 99 starch, have been accepted. 



CALCULATION. 



Supposing that 2.093 grms. substance had been used for the de- 

 termination of soluble and insoluble carbohydrates, and tliat, of the 

 sugar solution obtained by inversion, 2S c.c. had been required for 

 5 c.c Fehling's solution, we would find the starch by the following 

 equations : 



28 : 0.025 = 500 : X or X = 0.44 

 108 : 99 = 0.44 : X or X = 0.403 

 2.093 : 0.403 = 100 : X or X = 19.24 

 per cent, of insoluble carbohydrates (amylum). 



