Sugar is composed of oxygen, hydrogen, and carbon. There are three kinds, - cane sugar, or sucrose; grape sugar, or glucose; milk sugar, or lactose.
Cane sugar as an article of food closely resembles starch, but it is soluble and therefore more easily digested. It is readily distinguished by its sweet taste. It is found in many animal juices and also in fruits, but exists mainly in vegetable juices which have little or no acid in their sap, like sugar cane, rock maple, and beet-root. In its natural state it is dissolved in the vegetable fluids, mingled with many other substances. It is obtained by crushing the raw material; the fluids thus obtained are heated with a solution of lime, which causes the impurities to separate and rise in scum. These are removed, and the purified juice boiled down until it solidifies as a brownish deposit. This brown sugar is again dissolved, boiled, and filtered through charcoal, evaporated, and crystallized. Molasses is the drainage of the raw sugar. Brown sugar is the first product. Granulated sugar is brown sugar refined and re-crystallized. All brown and moist sugars are inferior in quality; they contain water and mineral matter, and are sometimes infested by a minute insect. Loaf sugar is the purest.
Sucrose, or cane sugar, is changed, by the acids of the gastric juice and the nitrogenous matter of the food, into grape sugar, or glucose. One of the most remarkable properties of sugar is that it can be decomposed and converted into other substances by fermentation. In its chemical relations sugar ranks with acids, and combines with bases, as in sugar of lead. It melts at 320°, and by cooling forms a transparent amber-colored solid known as barley sugar. If heated to 420°, it forms a brown mass, called caramel. Sugar has great preservative powers, and is used in preserving fruits, hams, bacon, etc.
Glucose, or grape sugar is abundantly distributed throughout the vegetable kingdom. It is found in honey, figs, grapes, and other fruits which have acid juices. It is less sweet than cane sugar, and is immediately absorbed into the circulation when taken into the stomach. It is less soluble and less easily crystallized than sucrose.
Lactose, or milk sugar, is obtained only from the milk of mammalia. It has the composition of cane sugar, and is converted into grape sugar when taken as food.
Fats, or oleaginous substances, are composed of carbon, hydrogen, and oxygen, - the two former elements preponderating, - and, having a very strong affinity for oxygen, are highly combustible.
Fats are solid; oils are liquid. Fats may be changed to oil by a slight accession of heat, and are obtained from both animal and vegetable tissues, - suet and dripping, from beef fat; lard, from the fat of pigs; butter, from the cream of milk; olive oil, from the fleshy pulp of the fruit of the olive tree. Oil is also found in nuts, seeds, cereals, and fruits. Croton oil, used for medicinal purposes, is from a plant, a native of India; cod liver oil, from the liver of cod fish; castor oil, from the seeds of the castor-oil plant.
Fats and oils contain three different oleaginous substances, known as stearine, margarine, and oleine. Oleine is that portion of oil that causes its fluidity. It is more abundant in oils than fats, and in the fat of swine than in the harder fat of sheep or beef. Lard is better than mutton fat or suet for frying, because, having more oleine, it can be converted into a liquid sooner. Margarine is harder than oleine. It exists in human fat, in butter, and olive oil. Stearine is the most solid substance of. the three, and is most abundant in tallow and suet.
The peculiar odor some fats and oils possess is from the presence of an acid. In butter it is butyric acid. Glycerine is the base common to all the fats. In stearine, the hardest fat, it unites with stearic acid; in margarine, a less solid form, with margaric acid; in oleine, or oil, with oleic acid.
"Fat forms the chief material of adipose tissue. It serves to fill spaces and give rotundity and beauty to the form, to equalize external pressure, to diminish the friction of the parts, to give suppleness to the tissues, and, being a non-conductor of heat, to keep the body warm. An undue accumulation of fat is a species of disease."
Oils and fats will not mix with water; but if an alkaline substance, like potash or soda, be added, the oil becomes separated into fine particles, and is held suspended in the watery fluid. This is called an emulsion, and this is what takes place in intestinal digestion. The gastric juice, being acid, does not digest fat, but only separates it from these substances, that it may digest the albuminous portions with which it is mingled. But the pancreatic fluid, being alkaline, resolves the fat into an emulsion. This completes the digestion, then the fats are absorbed and received into the general circulation. Having a strong affinity for oxygen, these fatty particles in the venous blood, when they come in contact with the oxygen of the air, burn, and heat is evolved. The power of. fat in maintaining heat and activity is two and a half times that of starch.
Oils which are used as food are fixed oils. Volatile oils are found in many condiments and perfumes. Volatile oils can be distilled, or changed to vapor, and recondensed into their original form; they leave no permanent stain on paper. Fixed or greasy oils cannot be distilled; before changing to vapor they recombine into new compounds.