374 Scientific Intelligence. 



By M. Caventou. — M. Caventou has ascertained several interesting facts 

 relative to the chemical changes which are occasioned by heat in fecula, 

 and has applied them ably in illustrating the nature of the different amy- 

 laceous substances of commerce, such as salop, sago, and arrow-root. 



Fecula, or starch, is characterised by its insolubility in cold water, by 

 forming a blue compound with iodine, and by dissolving in hot water, 

 with a due proportion of which it forms a paste. Chemists generally re- 

 gard this gelatinous mass as a hydrate of starch, but M. Caventou has 

 taken a different view of its nature. For he finds that paste cannot by 

 any means be reconverted into pure starch ; and that on mixing it with 

 a sufficient quantity of cold water, the greater part of it dissolves, a few 

 opaque white particles alone remaining, which are found, on examination, 

 to be unchanged starch. 



The change in the constitution of starch, by which it is rendered soluble 

 in cold water, is ascribed by M. Caventou to the influence of heat. When 

 dry starch is exposed to a temperature somewhat above 212° F. it acquires 

 a slight reddish tinge, emits an odour analogous to baked bread, and if ex- 

 posed, after cooling, to the action of cold water, it is dissolved. The same 

 effect is produced by boiling starch in water. M. Caventou regards this 

 modified starch as identical with the substance which M. Sauesure has 

 described under the name of amidine. Its essential character is to give a 

 blue colour with iodine, and to be soluble in cold water. The solution, 

 when evaporated, does not form a paste, but yields a hard, transparent 

 mass, like horn, which retains its solubility in cold water, and in which no 

 trace of pure starch can be detected. 



When dry starch is exposed to a still higher temperature than is suffi- 

 cient for converting it into amidine, a more complete change is effected. 

 It now dissolves with great facility in cold water, and gives a purple colour 

 with iodine. A similar effect is occasioned by long-continued boiling in water. 



Salop- 

 Salop, reduced to powder, forms with cold water a semifluid bulky gela- 

 tinous mass, which does not dissolve in that menstruum even by the aid 

 of heat, and which has all the characters of bassorine. Cold water dis- 

 solved nothing but saline matters and a small quantity of gum. The 

 solution did not give a blue colour with iodine, and therefore no amidine 

 was present. Boiling water took up a minute portion of starch, the pre- 

 sence of which was detected by iodine. Hence it follows that Salop is 

 composed of bassorine, with a small quantity of gum and of starch. 



Sago, Tapioka, and Arrow-root. 



When powdered sago is macerated in cold water for twenty-four hours, 

 it yields after filtration a perfectly clear solution, which forms a rich blue 

 with iodine. On macerating the residue in a fresh portion of water for the 

 same length of time, a solution is formed, which with iodine gives a blue 

 colour like the foregoing ; and by successive additions of cold water the 

 whole of the sago may be dissolved. Boiling water dissolves it still more 

 easily. The properties of tapioka are similar to those of sago. 



It hence appears that sago and tapioka have the character of amidine. 

 M. Caventou is of opinion that both substances originally exist in the 



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