The explanation is as follows: So strong is the affinity of the acid for the water that it breaks up the chemical combination between it and the carbon, unites with the water, and leaves the carbon free. So intense is the chemical change that an enormous amount of heat is evolved,--so much, in fact, that a considerable part of the water is vaporized, leaving the more or less solid charcoal. The light color noticed during the first part of the union indicates that the chemical dissociation is just beginning, and that only a small amount of carbon has been set free. =Glucose.= Glucose or grape-sugar (C_{6}H_{12}O_{6}) is one of the kinds of sugar found in grapes, peaches, and other fruits. It is about two and one half times less sweet than cane-sugar. It is manufactured on a large scale from the starch of corn. =Lactose.= Lactose or milk-sugar is the sugar found in the milk of the _Mammalia_. That of commerce comes chiefly from Switzerland, where it is made by evaporating the whey of cow's milk. For sweetening drinks for infants and for the sick, milk-sugar is said to be less liable to produce acid fermentation than cane-sugar, and also to be more easily digested. Sugar is a valuable nutrient, being very easily digested and absorbed. Cane-sugar is converted into glucose in the process of digestion by the pancreatic juice, and after absorption it is completely utilized in the body, furnishing heat and probably energy. =Effects of Heat on Sugar.= Sugar undergoes various changes, with different degrees of heat, by loss of some of its water of crystallization. One of the most remarkable of these is seen in caramel sauce, which is a rich crimson-brown syrup generally supposed to contain foreign coloring matter, but which does not. It is made by melting sugar without water, and heating it until the desired hue and thickness are reached. Nothing is added, but something is taken away; that is, some of the water is driven out, with the result of change in both color and taste. In a recent article in "The Century Magazine" (November, 1891) Prof. Atwater touches upon the subject of the production of artificial foods from the crude materials of the earth, and states, among other things, that a sugar resembling fruit-sugar has been made artificially by synthesis, by Prof. Fischer of Würzburg, Germany. AIR Air is a gaseous elastic body which envelops the earth on every side, extending possibly two hundred miles from its surface, but all the while growing more and more rare as the distance increases. When pure it is tasteless and odorless. We really live at the bottom of an atmospheric ocean, and are pressed upon by its weight. At the sea-level the pressure upon every square inch of surface is equal to fifteen pound.