96 Extracts from the Journals. Jan., 



on professional business, and where I had no means of prosecut- 

 ing my experiments. At my first period of leisure since, I resum- 

 ed my inquires, and have obtained certain results which may pro- 

 bably be found useful, as well as interesting. Before entering in- 

 to a detail of them, I shall shortly describe the constituents of 

 sound potatoes, according to the most authentic analyses. Their 

 average composition in one hundred parts, according to Einhof and 

 Lampadius, is — fibrous matter, 7 ; starch, 15 ; vegetable albu- 

 men, 1 ; gum, acids, and salts, 3.5 ; water, 75. Besides these 

 principles, Vauquelin, by his older and more minute analysis, dis- 

 covered the following in minute quantities: crystallizable aspara- 

 gin; an azotised substance resembling gum; a resinous matter 

 emitting an agreeable odor when heated; an extractive matter 

 which blackens in the air; citric acid; citrates and phosphates of 

 potash and lime. 



The fibrous matter of potatoes is not of the same species as that 

 of woody roots, but consists of a substance analogous to starch, 

 which swells in water, becomes transparent, dissolves for the most 

 part in dilute sulphuric acid, and affords gum and sugar, only by 

 the action of concentrated sulphuric acid. In some of Einhof 's 

 experiments, the gummy matter which remained after evaporating 

 the potato juice was saccharine, but he ascribed the formation of 

 this sugar to an alteration produced on a portion of the gum in 

 the course of analysis. Neither he nor Lampadius, nor even Vau- 

 quelin, found sugar in sound potatoes. There can be no doubt, 

 however, that, from several causes, potatoes may become sweet tast- 

 ed indicating that part of their starch is saccharified. Thus, by 

 exposing them to repeated alternations of temperature, a few de- 

 grees below and above that of melting ice, the formation of sugar 

 is so much promoted, that they grow soft with the production of a 

 syrup of so rich a nature, that it will not permit the potatoes to 

 solidify even when cooled several degrees below 32° Fahrenheit. 

 This curious transmutation seems to depend, at least in its origin, 

 upon a vital reaction; for when they are frozen very rapidly, no 

 sugar is formed either dviring or after their thawing; but, on the 

 contrary, potatoes so treated afford more starch than otherwise. 



The nutritious quality of potatoes resides chiefly in the starch, 

 fibrine, and albumine; the latter being essential to the formation 

 of blood. Boussingault rates the feeding of a cow for twenty- 

 four hours at fifteen kilogrammes (about thirty three pounds 

 avoirdupoise) of potatoes, and the quantity of azote in them at 

 fifty grammes, or gloth part of their weight. This w^ould give 

 -^Lth part of azote in dried potatoes. Now, since these contain 

 four times as much albumine as the moist ones do, we shall have 

 four per cent of albumen in them, according to the above analy- 

 sis, which four parts contain the whole of the azote in 100 parts 



