36 ■■£ M. Caventou's Chemical Researches on Starch, 



from thence the author concludes that the iodide of starch does 

 not exist, and consequently that there is no chemical action 

 between the iodine and the starch, and that it is only a 

 simple superposition of the molecules of the iodine on the 

 surface- of the grains of fecula. 



This experiment proves, in my opinion, that the grains of 

 fecula are not endowed with a porosity great enough to permit 

 the absorption of iodine into the interior of their substance : 

 and that as the chemical action is very feeble between these two 

 bodies, there is no disaggregation of the amylaceous molecule, 

 which then preserves its primitive form ; but it is no reason 

 for not admitting a combination, superficial as it may be. The 

 animal and vegetable tissues submitted to the processes of 

 dyeing, do they lose their pristine form by the fixing of the 

 colours? And notwithstanding I think it will not be said 

 that there is no combination. 



From the circumstance that the grains of fecula are all 

 formed and free in the cells of the vegetable; of their rounded 

 and smooth form ; of their unalterability in cold water, their 

 colouration by iodine and their discolouration by alkali, — M. 

 Raspail concludes that fecula is not an immediate principle of 

 vegetables ; and a series of experiments which he has made 

 seems to prove to him that the grains of fecula are organs 

 formed of a smooth integument, not to be attacked by acids at 

 an ordinary temperature, and of a substance therein inclosed, 

 which he thinks of the same nature as gum. We are about 

 to give in succession these experiments, and to discuss the 

 consequences of them. 



This author exposed some fecula to heat, in such a manner 

 as to carbonize the upper layer ; he then made haste to pro- 

 ject some parcels of the intermediate layer of fecula on the 

 object- slider, on the centre of which he put a drop of diluted 

 alcohol. All at once he saw currents become established, 

 grains of fecula attract and repel one another with the rapi- 

 dity of lightning ; and he "perceived, he says, certain gummy 

 traces which spread themselves slowly in the liquid, as if even 

 the much-diluted alcohol could thus permit the gum to diffuse 

 itself. The author adds, that if the fecula is coloured before it 

 is exposed to the action of fire, by the microscope we see the 

 liquor come out of it colourless ; with pure water, the experi- 

 ment is not so decisive, because this liquid too quickly dis- 

 solves the gummy part : nor are we constantly successful with 

 the diluted alcohol ; and we must always, according to the au- 

 thor, repeat the experiment often in order to see the liquid por- 

 tion come out of its envelope ; but we always find on the object- 

 slider a mass of insoluble integuments and a gummy substance 



which 



