1846.] Potato Disease. 97 



of dried potatoes, amounting to y^th, or one and one-third per 

 cent. But 100 parts of albumen, according to Dumas and Ca- 

 hours, contain 15.75 of azote, and four will therefore contain on- 

 ly 0.63, being about one-half the proportion of azote assigned by 

 Boussingault. Having, in the course of my frequently recurring 

 analysis of guano, contrived a method of determining its propor- 

 tion of azote, even to yo o^h "f a grain, or half a milligramme, I 

 have recently had recourse to this method in the examination of 

 potatoes. When a portion of these, in a dry, pulverulent state, was 

 subjected to ignition in contact with hydrate of soda and lime, 0.579 

 of azote were obtained from 100 parts of the potato ; a number 

 which accords well with that deduced from Dumas and Cahours' 

 results as applied to the proportion of albumine in potatoes, an ac- 

 cordance which seems to justify my determination. Potato, in its 

 ordinary moist state, will hence contain about 0.015 of azote, or 

 one and a half parts in a thousand. To this element, and the ani- 

 mal principles into which it enters, th'e nutritive quality of pota- 

 toes is to be ascribed, while their starch and starchy fibrine af- 

 ford the fuel of animal temperature. 



In the diseased potatoes, a portion of the starch is transformed 

 into sugar, and of the albumine into an acrid offensive brown sub- 

 stance. If such tubers as are characterized by brown spots in the 

 interior, and a thickened brown skin, both composed of fungous fi- 

 bres, be grated or sliced, and exposed to pressure, either alone or 

 with a little tepid water, the juice obtained will be found to have 

 a mawkish sweet taste, followed by a sense of pungency on the 

 tip of the tongue. If some of this juice be mixed with a little of 

 Trommer's grape-sugar test, (an alkalized solution of sulphate of 

 copper,) this blue-colored mixture will change into a bright or- 

 ange hue, slowly, in the cold, but rapidly on the application of a 

 gentle heat, with a deposit of protoxide of copper. By means 

 of a modification of that test, described by me in the Pharmaceut- 

 ical Journal for July, 1842, I have ascertained the existence of 

 about five per cent of saccharine matter in diseased potatoes; 

 yet by the same re-agent, which is insensible to yI^ of a grain of 

 sugar, I could observe none of it in a perfectly sound potato. 

 After satisfying myself, in this way, as to the presence of sugar 

 in diseased potatoes I proceeded to verify the fact by placing their 

 expressed juice, as also their infusion in contact with a little yeast, 

 at a fermenting heat of from 80° to 90° Fahrenheit, and watched 

 the resulting phenomena. A fermentative action soon began, and 

 in an hour or two became so brisk as to throw up a thick, creamy 

 froth, like that occurring with small beer wort. At the end of 

 thiry-six hours, the liquor having considerably diminished in 

 specific gravity, was subjected to distillation, and yeilded alcohol 

 equivalent to about four per cent of sugar in the potato. In ord- 



