THE VOLATILE PAKT OF PLANTS. 67 



albuminoid substances, the fats, the sugar, and dextrin, are brought 

 into such a condition that simple washing with alcohol or water suf- 

 fices to remove them completely. The chief part of the phosphoric 

 and silicic acids is likewise rendered soluble. The starch-grains 

 are not affected, neither does the cellulose undergo alteration, either 

 qualitatively or quantitatively. In fact, this treatment serves excellently 

 to isolate starch-grains for microscopic investigations. Besides starch 

 and cellulose nothing resists the action of alcoholic potash save portions 

 of cuticle, gum, and some earthy salts. 



When the digestion is finished, it is advisable, especially in case the 

 substance is rich in fat, to bring the contents of the tube upon a filter 

 while still hot, as otherwise potash-salts of the fatty acids may crystallize 

 out. It is also well to wash immediately, first, with hot absolute alcohol, 

 then, with cold alcohol of ordinary strength, and finally, with cold wa- 

 ter until these several solvents remove nothing more. In the analysis 

 of matters which contain much mucilage, as flaxseed, the washing 

 must be completed with alcohol of 8 to 10 per cent, to prevent the 

 swelling up of the residue. 



The filter should be of good ordinary (not Swedish) paper, should be 

 washed with chlorhydric acid and water, dried at 212, and weighed. 

 When the substance is completely washed, the filter and its contents 

 are dried, first at 120, and finally at 212. The loss consists of albumi- 

 noids, fat, sugar, and a part of the salts of the substance, and when the 

 last three are separately estimated, it may serve to control the estima- 

 tion, by elementary analysis, of the albuminoids. 



The filter, with its contents, is now reduced to powder or shreds, and 

 the whole is heated with water containing 5 per cent of chlorhydric 

 acid until a drop of the liquid no longer reacts blue with iodine. The 

 treatment with potash leaves the starch-grains in such a state of purity 

 from incrusting matters, that their conversion into dextrin proceeds 

 with great promptness, and is accomplished before the cellulose begins 

 to be perceptibly acted upon. By weighing the residue that remains 

 from the action of chlorhydric acid, after washing and drying, the 

 amount of cellulose, cork, lignin, gum, and insoluble fixed matters is 

 found. By subtracting these from the weight of the substance after 

 exhaustion with potash, the quantity of starch is learned with great ac- 

 curacy. The only error introduced by this method lies in the solution 

 of some saline matters by the acid. The quantity is, however, so small 

 as rarely to be appreciable. If needful, it can be taken into account by 

 evaporating the acid solution to dryness, incinerating and weighing the 

 residue. By warming with concentrated malt-extract at 332, the starch 

 alone is taken into solution, and no correction is needed for saline mat- 

 ters. If it is wished to determine the sugar produced by the transfor- 

 mation of the starch, a weaker acid must of course be employed. In case 

 of mucilaginous substances, the starch must be extracted by digest ion 

 with a strong solution of chloride of sodium, with which the requisite 

 quantity of chlorhydric acid has been mixed, and the residue should be 



