and the different amylaceous Substances oj Commerce. 367 



To proceed : " The soluble substance," says this author, 

 " not only loses in the open air the blue colour which the iodine 

 communicated to it, but moreover the action of heat takes 

 away its property of again becoming coloured. It is known that 

 the syrup of fecula is prepared by the apothecaries when iodine 

 no longer colours the amylaceous substance. This pheno- 

 menon has been attributed," he says, " to a metamorphosis 

 produced by a long ebullition : we were far from adopting 

 explanations of this kind so much used nevertheless in vege- 

 table chemistry, and the following observation is sufficient to 

 remove every idea of metamorphosis." 



See, now, the capital observation which prevents M. Ras- 

 pail's admitting the modifications so much used in vegetable 

 chemistry. 



"Evaporate," he says, "the soluble substance of the fecula 

 obtained as far as possible in the highest state of purity, and let 

 it be evaporated in layers not very thick ; a substance will be 

 obtained entirely similar to gum in its physical characters, and 

 its no longer colouring iodine, either in a solid state, or dis- 

 solved in water. The colouring of the fecula is then cer- 

 tainly owing only to a foreign and volatile substance, which 

 evaporation causes to disappear." — (Page 395.) 



What astonishes most in an assertion so new, and I would 

 almost say so unexpected, according to the preceding expla- 

 nations, is the facility with which M. Raspail admits the ex- 

 istence of a volatile substance which he neither saw nor ob- 

 tained : just now, the colouration was inherent in the membra- 

 nous form of the integuments and to that analogue which can 

 affect the gummy part in certain circumstances; and now, that 

 the microscope no longer indicates any trace of membranes 

 or of integuments, M. Raspail borrows from his imagination 

 a volatile substance, by the help of which he escapes from the 

 difficulty ; — this seems very convenient. Thus the integuments, 

 like the gummy part dissolved in water, now no longer become 

 coloured by iodine but by the help of a volatile substance ; but 

 then what becomes of the theory of the colouration and the de- 

 colouration of the filtered liquor, and proceeding from the em- 

 jpois diluted in cold water ? This colouration then is no longer 

 owing to the integuments that have passed through the pores 

 of the filter, but to the gummy part, which can affect in 

 this case a membranous form. It seems to me again very 

 difficult to reconcile all these different explanations of one and 

 the same fact, of which notwithstanding a simple chemical al- 

 teration gives in my opinion so satisfying an account. 



I shall follow up this examination no further: the various 

 citations which I have just made from the Memoir of M.Raspail 



will 



