§§ 193, 194. EXTRACTION. 209 



differing greatly from one another in solubility, etc. The majority 

 of them are characterized by a certain disposition to combine with 

 lime, potash, etc., and this has led to their classification with the 

 weak organic acids (arabic acid, etc.) ; in fact, some of the differ- 

 ences in solubility, etc., seem occasionally to depend directly 

 upon the quantity and quality of the bases with which they are 

 combined. 1 



But other substances, such as albumen, tannin, etc., that simply 

 accompany the pectin and mucilage, can also exercise an influence 

 on the behaviour of the latter to solvents. On this account, and 

 because, as a rule, such matters as mucilage diffuse but slowly, it 

 is not always possible, in extracting vegetable substances with 

 water according to § 71, to be certain that all the mucilage (arabin, 

 etc. ) soluble in water has really passed into solution. If heat were 

 employed, the amount dissolved would certainly be increased, but 

 at the same time other and more serious errors would be intro- 

 duced. 



One such source of error is to be found in the presence of 

 carbohydrates closely allied to soluble mucilage, but differing 

 from it in only swelling (not dissolving) in cold water (metarabic 

 acid, etc.). These carbohydrates are of frequent occurrence in 

 plants. Prolonged heating with water gradually dissolves them. 

 Error would also be caused by carbohydrates like lichenin, 

 caraghin, starch, etc., hot solutions of which gelatinize on cooling, 

 as well as by other substances. 



§ 194. Modified Method of Examination for Mucilage, etc. — For the 

 reasons given in § 19-3, I think it is preferable to extract with 

 cold water, and estimate the mucilage and albumen in the solution 

 prepared according to § 71. The washings mentioned in that 

 section should be evaporated to a syrup, in Avhich a similar deter- 

 mination of mucilage and albumen should be made. If the 

 material has been macerated with exactly 100 cc. of water, and 

 65 cc. of filtrate have been obtained (used for the first determina- 

 tion of albumen, etc.), then 35 cc. must be retained by the residue 

 and filter, and these 35 cc. must be extracted by the washing. If the 



^ This was clearly the case in peony-seed (Archiv d. Pharm. [3], xiv. 426, 

 1879 ; Journ. Chem. Soc. xxxv. 1043). Treatment of the seed with alcoholic 

 tartaric acid rendered far more arabic acid soluble in water than it was 

 possible to extract by direct treatment with the latter menstruum. It had 

 evidently been liberated from combination by tartaric acid, and rendered 

 soluble in water. 



14 



