78 SUBSTANCES SOLUBLE IX WATEB. 



removing ths lead by svilpliurettecl hydrogen and any glucose 

 that may be present by rapid fermentation. The residue may be 

 exhausted ■with boihng 90 per cent, alcohol and allowed to crystal- 

 lize in the cold. But an accurate result cannot be expected, since, 

 in addition to other errors, mannite may be produced in consider- 

 able cjuantity by the fermentation of cane-sugar.^ For particulars 

 of some substances allied to mannite see § 212. 



The method of examination for bitter principles, glucosides, and 

 alkaloids has been described in §,§ 58 to 69. (See also i^.^ 165 

 et seq. ; 171.) 



EXAMINATION FOR ALBUMINOIDS SOLUBLE IN WATER, 

 AMMONIACAL SALTS AND NITRIC ACID. 



§ 92. Extraction of Albuminoids. — It has already been observed 

 in § 74 that if the residue, after extraction with ether and alcohol, 

 be exhausted with water the estimation of albuminoids in the 

 aqueous extract thus jjrepared will generally give inaccurate 

 results. A fresh portion of material should therefore be directly 

 exhausted -with water, or, if much fixed oil is present, the extrac- 

 tion with water may be preceded by treatment with petroleum 

 spirit. After having removed the fixed oil (if necessary) from 

 about 10 grams, the residue is dried at 40° C, macerated with 

 100 cc. of water, with freqvient agitation, for 4 to 6 hours, and 

 filtered as described in § 71. Jf thought desirable the maceration 

 may be conducted at a temperature not exceeding 35° to 40°. 

 (Comj^are also § 225 et seq.) 



Detection. — With a portion of the filtrate qualitative experi- 

 ments should be made. Among the reagents used for the detec- 

 tion of albumen, iodine and mercuric nitrate (containing as little 

 free nitric acid as possiljle) may be mentioned ; the former colours 

 it brown, Avhilst the latter produces a yellow colour, changing, on 

 the addition of a trace of nitrous acid, to a splendid red. The 

 addition of caustic potash to albumen, previously moistened with 

 solution of sulphate of copper, is followed l)y the appearance of a 

 bluish-violet colour. If the amount of albumen present ho rather 

 small, these experiments may be made with the i)recii)itates ob- 

 tained l)y the addition of an acid to the aqueous solution (§ 93). 



Microchemical. — These reagents also serve for the microchemical 

 detection of albumen. The latter substance possesses, moreover, 



^ Archiv d. Pharm, xv. 17 (Journ. Chem. Soc. xxxviii. 100\ 



