S. W. Johnson— Composition of the Sweet Potato. 199 



The total loss of water experienced by the fresh substance = 

 73-39 per cent. 



Fat was extracted from the dried-residue of the water-estima- 

 tion, by treatment with carbon disulphide in the apparatus 

 before described. The process required twelve hours tor com- 

 pletion. Two trials yielded 0-26 and 0-31 of a soft yellow 

 substance, appearing at first like a pure fat, but which to the 

 feel and taste had more of the properties of wax than of the 

 ordinary fats. It probably resides chiefly in the laticiferous 

 tissue, whose yellow juice is evident on a" fresh section of the 

 sweet potato. 



An aqueous extract of the sweet potato was obtained by 

 digesting four grms. of finely-pulverized air dry substance 

 with nearly half a liter of cold water for five hours and filter- 

 ing. The residue was treated with a similar quantity of cold 

 water for twelve hours more. Aliquot portions of the two 

 extracts were separately evaporated in capsules and dried at 

 212° F. The first extraction v» a- [>racth \\ > mplete, as the 

 second digestion took up but 3"5 mgr., or a little more than T V 

 per cent of soluble matters. The total amount of solid aqueous 

 extract, after deducting ash, was 7"94 per cent. 



The aqueous extract was brown in color and perfectly clear. 

 Boiled, it gave a very slight precipitate, acids made it turbid, 

 and Ifillon'a test b the liquid on heating. 



Iodine gave no coloration. Basic lead acetate gave a copious 

 precipitate, separating in flocks on boiling, and in the filtrate 

 Fehling's solution gave reddish-yellow precipitate on boiling. 

 These react :■ Lice of a trace of albuminoids, of 



gum* and of a glucose. They exclude starch, amylodextrin 

 and dextrin.f 



To effect proximate separation of gum and sugar, a portion 

 of aqueous extract was e\ morated to dryness, taken up in a 

 very little water and treated with 80 per cent alcohol. Sugar 

 was recovered by evaporation of the alcohol solution. As is 

 known, this separation is a rough one. The sugar obtained 

 gave on boiling with Fehling's solution, at once, a copious 

 flocky-red precipitate. Set aside in concentrated solution it 

 showed do s ition. It therefore largely con- 



sisted of a glucose. Its amount was 6"86 per cent. The 

 substance remaining insoluble after a second treatment with 

 alcohol, which was mostly gum, was 1-08 per cent of the fresh 



Cellulose was determined by alternate treatment of the po< 

 dered substance with dilute (2 percent) sulphuric acid and — - 



ie der Starkegruppe, p. 1 



