CANNACEiE. 



starch is resolved into Dextrin, (J'-'WO'', and Dextrose, 0'W0\ with 

 which decomposition, the fornuila, C^^ff'^O'^ would he more in accord. 

 Sachsse (1877) on the other hand advocates the formnla C=^'^H^-0''H 

 12 Om • 



Cold water is not without action on staf ch ; if the latter be con- 

 tinuously triturated with it, the filtrate, in which no particles can he 

 detected hy the microscope, will assume a blue colour on addition of 

 iodine, Avithout the formation of a precipitate. The proportion of starch 

 thus brought into solution is infinitely small, and always at the expense 

 of the integrity of the grains. It is even probable that the solution in 

 this case is due to the minute amount of heat, wdiich must of necessity 

 be developed by the trituration. 



Certain reagents capable of attacking starch act upon it in very 

 different ways. The action in the cold of concentrated aqueous solutions 

 of easily soluble neutral salts or of chloral hydrate is remarkable. 

 Potassium bromide or iodide, or calcium chloride for instance, cause the 

 grains to sw^ell, and render them soluble in cold w^ater. At a certain 

 degree of dilution a 2:)erfectly clear liquid is formed, which at first con- 

 tains neither dextrin nor sugar ; it is coloured blue, but is not precipi- 

 tated by iodine w^ater; and starch can be thrown clow^n from it by alcohol. 

 This precipitate, though entirely devoid of th e structural peculiarity of 

 starch, still exhibits some of the leading properties of that substance ; 

 it is coloured in the same manner by iodine, does not dissolve even 

 when fresh in ammoniacal cupric oxide, and after drying is insoluI)le 

 in water, whether cold or boiling. The progress of the solvent is most 

 easily traced when calcium chloride is used, as this salt acts more slowly 

 than the others we have mentioned. It leaves scarcely any perceptible 

 residue. This fact in our opinion militates against the notion that 

 starch is composed of a peculiar amylaceous substance, deposited within 

 a skeleton of cellulose. 



The remarkable action of iodine upon starch was discovered in ISH 

 by Colin and Gaultier de Claubry. It is extremely different in degree, 

 according to the peculiar kind of starch, the proportion of iodine, and 



tlie 



nature of the substance the grains are impregnated with, before or 

 after their treatment with iodine. The action is even entirely arrested 

 (no blue colour being produced) by the presence in certain proportion 

 of quinine, tannin. Aqua Picis, and of other bodies. 



The combination of iodine wath starch does not take place in equi- 

 valent proportions, and is moreover easily overcome by heat. The iodine 

 combined with starch amounts at the utmost to 7o per cent. The 

 compound is most readily formed in the presence of w^ater, and then 

 produces a deep indigo blue. Almost all other substances capable ot 

 penetrating starch grains, weaken the colour of the iodine compouncl to 

 violet, reddish yellow, yellowy or greenish blue. These different shades, 

 the production of which has been described by Ntigeli wdth great diffuse- 

 ness are merely the colours which belong to iodine itself in the solid, 

 iiqnid or gaseous form. They must he referred to the fact that the 

 particles of iodine diffuse themselves in a peculiar but hitherto unex- 

 plained manner within the grain or in the swollen and dissolved starch. 



rn,^^""'"'^'"'^? °^ Arrowroot— The chief kinds of arrowroot found in 

 commerce are known as Bei^uda, St. Vincent, and Natal; but that of 



