§§ 71, 72. TREATMENT WITH WATER, ETC. 65 



V. 



Examination of Substances Soluble in Water, 



mucilage, acids, glucoses, saccharoses and other 

 carbohydrates, albuminous substances, etc. 

 § 71. Treatment with Water. — The residue of the material after 

 exhaustion with alcohol (§ 47) is dried at a temperature not above 

 40° C, and transferred to the vessel previously used, which should 

 likewise be dried. Water is then added in the proportion of at 

 least 10 cc. for every gram of original substance, and the whole 

 frequently shaken during twenty-four hours. The liquid is now 

 filtered off through the same filter that has already served for 

 such operations, and the filtrate set aside for examination. The 

 residue is Avashed by repeated maceration and filtration, the wash- 

 ings being reserved for treatment as directed in § 194. The in- 

 soluble substance is not dried (§§ 92, 102, 105 et seq. ; 193 et seq.). 



§ 72. Total Solid Residue. — 10 cc. of the filtrate are evaporated 

 in a tared platinum dish, dried at 110° and weighed. The resi- 

 due is then incinerated and the ash deducted. It should be 

 ascertained if the ash is rich in carbonic, sulphuric, or phosphoric 

 acid, chlorine, lime, magnesia or potash ; and if large quantities of 

 sulphuric or phosphoric acid are present they should be estimated 

 (§ 82). 



If the filtrate contain much siigar, moisture may easily be re- 

 tained by the residue. In such cases Serrurier^ advises the addi- 

 tion of h per cent, of alcohol before evaporation. It is claimed 

 that the residue is then porous and easily dried. 



EXAMINATION OF MUCILAGINOUS SUBSTANCES, DEXTRIN AND 

 ALLIED CARBOHYDRATES PRECIPITATED BY ALCOHOL. 



§ 73. Mucilaginous Substances. — 10 to 20 cc. of the aqueous 

 extract (§71) are mixed with two volumes of absolute alcohol, and 



^ Zeitschr. f. anal. Chemie, x. 491. 



