288 M. Caventou's Chemical Researches on Starch, 



These results make me think that iodine is really susceptible 

 of forming a combination with starch ; and what in my mind 

 supports this opinion is the following fact. If, to the above 

 liquor filtered and brought to a purplish colour by iodine, a 

 little amidine or starch be added, at the same instant these two 

 bodies take away the iodine from the substance which causes 

 the purplish colour, and produce a blue combination, which 

 remains dissolved if produced by the amidine, and which be- 

 comes precipitated if it is owing to the starch. If this last 

 combination is isolated by the filter, we may again succes- 

 sively reproduce, as above, the purple and blue colours. — 

 Does not this fact prove that there is really a chemical action 

 between iodine and starch, and that the colouring is not deter- 

 mined merely by a physical effect, as M. Raspail has advanced? 

 — when there is a very evident affinity, can we call in question 

 the chemical action ? 



Application of the preceding observations to the investigation 

 of the amylaceous substances of commerce. 



As I have said at the beginning of this memoir, I had at 

 first begun at once the study of salep, of sago, of tapioca, and 

 of arrow-root ; and the chemical phenomena which I had ob- 

 served with these substances had induced me to admit sago 

 and tapioca especially, as new species of starch. But I had 

 made my experiments under the notion that fecula was per- 

 fectly known to us in all its chemical properties ; and it is this 

 which made me deduce from my results a consequence in a 

 certain degree premature: but the facts which I published 

 at this period will remain altogether the same ; I shall only 

 differ in the way of considering and explaining them. 



Of Salep. 



(This article is extracted literally from my notes, I have 

 not altered any thing in them.) 



Salep reduced to powder and put in contact with cold wa- 

 ter becomes easily diluted by agitation, and forms a sort of 

 half-liquid and translucid empois. This empois, diluted in a 

 sufficient quantity of cold water and thrown on a filtre, gives 

 a transparent gummy liquid of a saltish taste. There re- 

 mains on the filtre a gelatinous trembling matter, insoluble 

 in water, whether hot or cold, but which augments consider- 

 ably in volume in this liquid. This gelatinous substance, se- 

 parated from all the soluble principle, first by cold water and 

 then by boiling water, was set aside to be examined. — It will 

 be spoken of hereafter. 



Aqueous 



