250 STARCH, LICHENIN, ETC. 



and yelhw, according to the colour they yielded Avith iodine. 

 These two were connected by intermediate modifications striking 

 violet, reddish and reddish yellow colours with iodine, differences 

 which are probably referable to variations in the density. In accord- 

 ance with this theory the several modifications vary in the resistance 

 they offer to solvents and chemical agents. As the blue modification 

 is the most easily attacked, it might be considered to be that of 

 lowest density. It is followed by the violet, red, etc., in succes- 

 sion up to the yellow, the densest form of which shows a great 

 resemblance to cellulose. When starch is boiled the blue modifi- 

 cation passes into solution, carrying with it a little of the yellow. 

 If the former is removed by allowing it to decompose, the yellow 

 modification separates out. From a solution of the latter, pre- 

 pared by prolonged boiling with water and concentrating, crystals 

 of amylo-dextrin can be obtained, which are coloured yellow by 

 iodine. 



The bodies above referred to occur in different proportions in 

 the different varieties of starch, and the amount of either present 

 might possibly be found to be characteristic of the starch under ex- 

 amination. It might, for instance, be ascertained by comparative 

 experiments how long the action of an acid of certain strength 

 must be continued before the blue or red colouration with iodine 

 ceases to be produced. For the isolation of the yelloiv modification, 

 formerly called cellulose, y amnion (Bechamp), I have recommended 

 digestion at a temperature not exceeding 60°, with 40 parts of a 

 saturated solution of chloride of sodium containing 1 per cent, of 

 hydrochloric acid, and washing with water and dilute spirit. I 

 have thus obtained 3'4 per cent, from arrowroot, 2*3 per cent, 

 from wheat-starch, and 5 7 per cent, fi'om potato-starch. 



§ 244. Hydrocelhilose. — A blue colouration of the cell-wall is fre- 

 quently noticed when sections of vegetable substances are moistened 

 with iodine water. It was probably this reaction that gave rise to 

 the theory that a modification of cellulose could occur striking a 

 blue colour with iodine, 



I do not concur in this view ; in fact, I am convinced that in 

 such cases the cell-wall in question contains besides cellulose, which 

 is characterized by its power of resisting the action of chlorate 

 of potash and nitric acid, other carbohydrates (amyloid), probably, 

 at least m part, of the composition 012^22^11' agreeing therefore 

 in this rcs})ect with arable acid, pararabin, etc. Whether these 



