§§ 229, 230. ESTIMATION. 237 



means of the tannin reagent mentioned in § 95, and Cramer- 

 Dolmatow has found that extracts from one and the same plant 

 yield concordant results when titrated with the same reagent. It 

 must be left, however, for further experiments to show what veget- 

 able albuminoids can be estimated in this way. 



§ 230. Estimation contimied. — A gravimetric estimation unth tannin 

 will generally yield higher results than can be obtained by coagu- 

 lation (§ 94). The source of the difference is to be looked for 

 partly in the deficiencies of the latter method, and partly in 

 the fact that a number of albuminous substances soluble in 

 water are not coagulated by boiling with dilute acetic acid, but 

 are nevertheless precipitated by tannin. For this reason the 

 results obtained b}^ the tannin-method will generally agree better 

 with those yielded by precipitation Avith alcohol. Nevertheless, 

 I do not recommend the omission of the estimation by coagulation, 

 for if the difference is considerable, that is, if the estimation by the 

 tannin-method yields much higher results than that by coagula- 

 tion, it i^roves that another albuminous substance is present, which 

 is not coagulated by boiling. It is only Avhen the difference is 

 small that the presence of vegetable albumen alone may be in- 

 ■ ferred ; it may then be estimated by precipitation by tannin. 



To render the coagulation-test as reliable as possible, I have 

 recommended chloride of sodium to be added, and the precipitate 

 to be washed, first Avith boiling water, and subsequently with 

 dilute spirit. If the chloride of sodium is omitted the precipita- 

 tion is generally less complete, and prolonged washing, especially 

 with cold water, is liable to redissolve part of the albumen. 



Ferments. — Simultaneously with the albumen a number of other 

 substances may be partially or wholly precipitated, which, although 

 agreeing with albumen in many respects, have been too little 

 investigated from a chemical point of vieAv to justify their being 

 classed straightway as albuminoids. I refer to the so-called fer- 

 ments. Like albumen, they contain nitrogen, and are precipitated by 

 strong alcohol, etc. ; most of them, probably, are coagulated like, 

 or together Avith, albumen Avhen boiled in aqueous solution. They 

 are distinguished from albumen by their fermentative action, which 

 evinces itself in various Avays. Diastase, like saliva, converts 

 starch into sugar, whilst invertin changes saccharose into invert- 

 sugar. Vegetable ferments allied to pepsin (papayotin) peptonize 

 albumen. Myrosin decomposes myronic acid, emulsin amygdalin ; 



