Elements of agricultural chemistry, in a course of lectures of the Board of Agriculture / [Sir Humphry Davy].

  • Humphry Davy
Date:
1814
Catalogue details

Licence: Public Domain Mark

Credit: Elements of agricultural chemistry, in a course of lectures of the Board of Agriculture / [Sir Humphry Davy]. Source: Wellcome Collection.

    108/532 (page 76)
    arts, particularly in calico-printing’: till lately, in this country, the calico-printers used gum arahic; but many of them, at the suggestion of Lord Dun- donald, now employ the mucilage from lichens. 2. Starch is procured from diderent vegetables, but particularly from wheat or from potatoes. To make starch from wheat, the grain is steeped in cold water till it becomes soft, and yields a milky juice by pressure; it is then put into sacks of linen, and pressed in a vat filled with water: as long as any milky juice exudes the pressure is continued ; the fluid gradually becomes clear, and a white pow- der subsides, which is starch. Starch is soluble in boiling w^ater, but not in cold water, nor in spirits of wfine. According to Dr. Thomson, it is a characteristic property of starch to be soluble in a warm infusion of nutgalls, and to form a precipitate when the infusion cools. Starch is more readily combustible than gum; when thrown upon red hot iron, it burns w ith a kind of explosion, and scarcely any residuum re- mains. According to Mr. Gay Lussac and The- nard, 100 parts of starch are composed of Carbon, with a small quan- tity of saline and earthy j y 43,5o matter - - ^ * 1 Oxygene 49,68 riydrogene 6,77