“Around thee shall glisten the loveliest amber
That ever the sorrowing sea-bird has wept.”
Amber is not soluble either in water or alcohol; it is, however, soluble in sulphuric acid. It takes a good polish, and when rubbed is very electrical. It is composed of water, an acid, some oil, and an inflammable gas, which goes off when the amber is distilled.
The well-known camphor is got from a tree called the “Laurus Camphora”; it is a white, waxy substance, and can be obtained by oxidizing certain volatile oils. It is generally produced from the Laurus Camphora in a “still.” The behaviour of a piece of camphor in pure water is curious, but its motions can be at once arrested by touching the water or dropping oil on the surface. This phenomenon is due to the surface tension of the liquid, which diminishes when it is in contact with the vapour of the substance.
Nitrogenous Substances.
There are certain albuminous compounds which we must mention here. These are albumen, fibrine, and caseine. Albumen is the white of egg; fibrine is, when solid, our flesh and muscular fibre, while caseine is the substance of cheese. These are very important compounds, and the albuminous bodies are of the very highest importance as food, for the solid portion of blood, brain, and flesh consist, in a great measure, of them. Albumen, fibrine, and caseine contain carbon, hydrogen, nitrogen, and oxygen, with sulphur and phosphorus.
Albumen. The most familiar and the almost pure form of albumen is in the white of eggs, which is albuminate of sodium. It also exists in the serum of the blood, and therefore it is largely found in the animal kingdom. It can also be extracted from seed or other vegetable substances, but it is essentially the same. Albumen is very useful as an antidote to metallic poisons. It forms about 7 per cent. of human blood. It is soluble up to about 140° Fah.; it then solidifies, and is precipitated in a white mass. Albumen is used in the purification of sugar, etc.
Fibrine is found in a liquid condition in blood. The vegetable fibrine (gluten) is prepared by kneading wheat flour in a bag till the washings are no longer whitened. Like albumen it is found both in a solid and liquid state.
Caseine is seen in the skin which forms upon milk when heated, and forms about 3 per cent. of milk, where it exists in a soluble state, owing to the presence of alkali; but caseine, like albumen, is only soluble in alkaline solutions. As we have said, it is the principal constituent of cheeses. Caseine is precipitated by the lactic acid of milk, which is produced by keeping the milk too warm. Caseine, or curds, as they are called, are thus precipitated. The milk is said to be “sour,” or turned.