312 Caventou on the CJiemical Properties of Starch. 



the action of hot water. In paste, therefore, the fecula is not 

 merely hydrated, but is essentially modified. In this state, it 

 still possesses the characteristic and well known property of 

 forming a blue compound with iodine. It seems to be quite the 

 same as the amidine of M. de Saussure ; w^ho imagined, how- 

 ever, that the principle he procured was the result of putrefac- 

 tion. It was not, according to Caventou, the result of putrefac- 

 tion, but was formed in consequence of the action of hot water 

 on the undeccmposed part of the fecula. 



When amidine is boiled long in water, it loses its property of 

 striking a blue colour with iodine, causes a purple tint instead, 

 and has become much more soluble. The same change of pro- 

 perties may be effected by mere heat, namely by a higher de- 

 gree of torrefaction than that required to form amidine ; or it 

 may likewise be very readily effected by boiling starch in water 

 acidulated with a twelfth part of sulphuric acid. In this state, 

 it has not so great an affinity for iodine, as in the state of ami- 

 dine ; for if a little paste be mixed with the purple compound, 

 the colour becomes immediately bhie. 



When starch or amidine is boiled still longer, it becomes still 

 more soluble ; and iodine does not cause any change of colour on 

 it at all. Most of these facts, particularly the property pos- 

 sessed by heat, of rendering dry fecula soluble, more or less, in 

 cold water, have been familiar to chemists since the researches 

 of Vauquelin and Bouillon-la-Grange ; but the merit of ta- 

 king a connected view of the whole changes induced by heat 

 and water, and of associating those caused by heat alone with 

 those caused by boiling water, seems to belong to Caventou. 

 He might have stated more distinctly, however, than he has 

 done, where our former knowledge ended, and his discoveries 

 begin. 



Of the substances in commerce usually considered as amylace- 

 ous, Salep, according to the analysis of Caveqtou, ought not to 

 be accounted such. It yields a considerable quantity of matter 

 to cold water ; and the properties of this portion, both when dis- 

 solved and when dried by evaporation, are almost precisely the 

 same with those of gum. The residue, after the action of cold 

 water, is a tremulous, jelly-like mass, which, when treated with 

 boiling water, enlarges in volume, but imparts only a small quan- 



