88 SUBSTANCES SOLUBLE IN DILUTE SODA. 



VI. 



EXAMINATION OF SUBSTANCES SOLUBLE IN DILUTE CAUSTIC 

 SODA ; METARABIC ACID, ALBUMINOUS SUBSTANCES, PHLOBA- 

 PHENES, ETC. 



103. Extraction. The residue insoluble in water (71) is sus- 

 pended, whilst still moist, in water containing a known quantity 

 (about O'l to 0-2 per cent.) 1 of caustic soda in solution, using 

 about 10 cc. of alkaline liquid for every gram of original 

 substance. After standing for about twenty-four hours, with 

 frequent agitation, the mixture is filtered. From 20 cc. to 50 cc. 

 of the nitrate are acidified with acetic acid, mixed with 3 volumes 

 of 90 per cent, alcohol, and allowed to stand for twenty-four 

 hours in a cool place. The precipitate is then collected on a tared 

 filter, washed with 75 per cent, alcohol, dried, and weighed, de- 

 ducting ash. This precipitate usually consists of mucilaginous 

 substances (pectin) and albuminoids. The former generally cor- 

 responds to Scheibler's metarabic acid ( 195). 



104. Detection and Estimation of Albumen. If Lassaigne's test 

 shows the presence of a considerable quantity of albuminous sub- 

 stances, these should be estimated and deducted. To this end 

 another portion of the filtrate is precipitated as in 103, the 

 nitrogen in the precipitate estimated and calculated into albu- 

 minoids ( 224). This amount is then deducted from the weight 

 of the precipitate in 103. (See also 22G et seq; 236 to 238.) 



105. Estimation. But the amount of albuminous substances in- 

 soluble in water thus found cannot be noted as such in the summary 

 of results unless it corresponds to that calculated from the nitrogen 

 in the residue insoluble in water, as directed in 96. If the latter 

 is lower, it is to be regarded as the more accurate of the two ; the 



1 Not more, otherwise starch is attacked. 



