of Cellulose in Starch-grains. 247 



raised to 158° F., at which point unaltered starch-grains are 

 very quickly entirely dissolved. 



It is therefore evident that a strong expansive quality exists 

 only in the starch-substance which can be extracted by saliva, 

 and that the intimate combination in which the two substances 

 composing the grains stand in the grains must have a modify- 

 ing effect upon their respective properties. While the starch- 

 substance is in the fresh grain protected by the substance inso- 

 luble in saliva from the solvent action of cold water, when it 

 swells up from the action of hot water, &c., it carries the latter 

 with it in its expansion, and transfers the solution to which it 

 is subject by the action of saliva at a proper temperature, to 

 the substance which in a pure condition is altogether unaffected 

 by saliva. 



The substance insoluble in saliva is regarded by Nageli, as 

 above mentioned, as cellulose. In investigating the grounds on 

 which he makes this determination, we must first of all consider 

 the characters which Nageli uses for distinguishing cellulose and 

 starch. He says (pp. 182, 189) : The reaction with iodine forms 

 an essential distinction, and at the same time the only discrimina- 

 tive test J between starch and cellulose. Iodine colours starch, when 

 acting weakly, wine-red or violet ; more strongly, indigo-blue or 

 black : pure cellulose, on the contrary, is coloured from pale 

 and dirty reddish to copper-red or reddish brown. Cellulose is, 

 on the other hand, also coloured blue when softened by sulphuric 

 acid, and likewise when saturated with tincture of iodine, dried, 

 and afterwards wetted with water. Since the cellulose is here 

 softened as by sulphuric acid, perhaps iodic or hydriodic acid 

 (or both) may be formed; Nageli thinks the formation of iodic 

 acid probable. The action of sulphuric acid and the drying up 

 with iodine so transform the condition of aggregation of cellu- 

 lose, that it behaves like starch with iodine, or, as Nageli thinks, 

 is converted into starch. 



This interpretation of facts, which in themselves are certainly 

 true, is, in my opinion, altogether incorrect. Whether iodine 

 produces a red colour (rising from wine-red, through beautiful 

 purple, to deep violet), or a blue colour (from the brightest sky- 

 blue to deep indigo and apparent black), depends neither on the 

 circumstance that the object is starch or cellulose, nor upon the 

 quantity of iodine, but essentially upon the conditions of the 

 organic substance in respect to water. When very little water 

 is taken up, we have a red, when more, a blue colour. By 

 attending to this point, we may colour cellulose the finest blue, 

 and starch red and violet, without any chemical alteration of the 

 object. 



It is self-evident that a greater or less sweUing-up of the 



