The following description of this essential article of food, the use of which is now universal, and which forms so important an ingredient in the economy of vegetable nature, j is extracted from a new work by Dr. Pierce, I lately published, and which will be found no-[ ticed in our review of new publications :— " The physical properties ot sugar are so well known, that it is unnecessary to describe them. Sugar is very soluble in water and diluted spirits, is almost insoluble in absolute alcohol, and is entirely insoluble in ether. In our market only two sorts ot sugar are met with, the cane and the maple sugar, while I in different parts of Europe two other sorts occur, the beet and grape or starch-sugar.— Another variety, sugar of milk, is sometimes prepared for pharmaceutical purposes. But this article has little in common with the other sugars, except the name, and a sweetish taste. The cane, beet, and maple sugars have ; about the same sweetening power ; the grape-: sugar has much less, and the sugar of milk less than grape-sugar. The principal impurities to be sought for in cane-sugar are inorganic matter, water, molasses, farina, and grape or starch-sugar. The latter substance, though extensively added in Europe to cane-sugar, is not, I think, much, if at all, used for adulterating in this country. It may be detected by the action of concentrated sulphuric acid and of a solution of caustic potassa ; the lormer blackens cane-sugar, but does not affect the starch-sugar, while potassa darkens the color of starch-sugar, but does not alter that of cane-sugar. But the Copper Test is far more delicate. Add to the solution to be tested, a few drops of a solution of blue vitriol, and then a quantity of potassa solution, and apply heat ; if the cane-sugar is pure, the liquor will remain blue, while, il it be adulterated with starch-sugar, it will assume a reddish-yellow color. Sugar of milk acts with the copper test in the same way as starch sugar. Inorganic matter is determined by incinera tion, farina by the Iodine Test, water by drying at 212 , and molasses by getting rid of it by recrystallization from alcohol, as also by the color and moisture of the article. The natural impurities of sugar are gum and tannin ; gum is detected by giving a white precipitate with diacetate of lead, and tannin by giving a black coloration or precipitate with persulphate of iron. An experienced sugar dealer easily judges of the value of sugar by the taste, smell, specific gravity, moisture, and general appearance. The value of molasses may be determined by drying at 220 , and by the taste.
This article was originally published with the title "On Sugar" in Scientific American 8, 31, 242 (April 1853)