842 Transactions of the American Institute. 



ON THE SWEET PRINCIPLE IN FROZEN POTATOES. 



It is a well known fact that the nutritious root of Solanum tubero- 

 sum is getting sweet in freezing, and especially is this the case when 

 it has been exposed to cold for several times. The supposition was 

 made, that this change might be due to the conversion of the starch 

 of the potatoe into sugar, but I neither know of this hypothesis 

 being verified, nor am I acquainted of it ever being attempted to 

 be explained. It remains to be decided also whether sweet prin- 

 ciple exists already in the raw, or but in the boiled root. To 

 decide upon these questions, I exposed one pound of this vege- 

 table to the cold of a severe winter night, and when they were 

 thoroughly frozen, I reduced first, one-quarter of a pound of them 

 to a fine pulp, in a rasping machine, pressing the sap through a 

 flannel ; from this I measured 100 cubic centimeters (3.38 fluid 

 ounces), added to them ten per cent of a solution of basic acetate 

 of lead, shake.d the mixture well and filtered it finally through 

 coarse blotting paper. The clear liquid was transferred in the 

 glass tube of Mitscherlich's polarimeter, and the same interposed 

 between Nichols' prisms. There was, however, no rotation of the 

 plan of polarization to be noticed, and thus the fact was ascertained 

 that no sugar is present in raw frozen potatoes. 



For the purpose of deciding whether sugar is produced in the 

 process of cooking, I steamed 250 grammes of the vegetable for 

 one hour, crushing them afterwards with 200 cub. cent of tepid 

 water. The thus obtained solution was divided in two portions, 

 one of them was set aside, and from the other I precipitated gum 

 and protein matters, with sub-acetate of lead, in discoloring also 

 the reddish-brown liquid perfectly with a few drops of oil of vitriol. 

 In filling the same in the sugar tube, and rotating the analyser of 

 the polarimeter to its left, a change of color was instantly observed, 

 thus indicating the presence of uncrystalizable sugar. No calcula- 

 tion, however, was made from this rotation, as the rotation of the 

 uncrystalizable or fruit sugar to the left is compensated by dex- 

 trine and other substances, w^hich are right handed with respect to 

 polarized light, they being generally the product of the action of 

 heat upon albuminous starchy matter. 



I therefore made recourse to Fihling's test, in using the infusion 

 of the boiled potato, w^hich had been set aside. Then the follow- 

 ing two elements were determined: 1. The percentage of sugar in 

 the infusion. 2. The amount of water in the boiled potato. 



