Page images

them theit nutritious qualities. When evaporated to dryness; it forms portable soup, size, glue, &c. The union of this latter substance in the skin with tannin constitutes leather: I singlass is gelatine procured from certain parts of several fish, particülarly the sturgeon. The tendons and membranes of the body are chiefly gelatine.

Fibrin, or animal fibre, forms the basis of the muscular, or fleshy parts of animals. It is there combined with albumen, and remains with it after all the soluble parts of the flesh have been separated by water. It may also be obtained from blood, by washing the clot or coagulum in water, till a white fibrous matter remains. Fibrin is not soluble in cold water, but is very slightly so in boiling water. It is soluble in acids and alkalies, and by its union with the latter a soap is formed. Chaptal employed this property to make a soap from wool. It is very analogous to vegetable gluten.

Albumen is the principal constituent of the serum of blood, and is also called coagulable lymph. The white of eggs consists almost entirely of albumen. It is miscible with cold water, but is coagulated by heat, which forms the best test of its presence. It is also coagulated by acids and alkohol.

Mucus.- This substance in animals appears intended to lubricate or smooth certain parts of the body, and seems very analogous to a solution of gum. However, Dr. Bostock has shown that it differs from gelatine, as it cannot in cold water be brought to assume the gelatinous state. Tannin precipitates gelatine, but not mucus; whereas subacetate of lead, (extract of Goulard,) forms a precipitate with mucus, but not with gelatine. Mucus is found in saliva, tears, in the intestines, joints, &c.

Oil.--Animal oils are fat, tallow, butter, &c. They are mostly solid at the usual temperature. They may be rendered fluid by heat. Oil is obtained in great quantities from certain fish, partiçularly the whale, seal, &c. and fish oil continues fluid. It is very similar to vegetable oil in its other properties. Spermaceti somewhat resembles wax, and is obtained from the head of a species of whale. Animal fibre may be converted into a substance like spermaceti by treatment with the nitric acid, or by exposing it to a current of running water for several months. This has been called adipocire. It has been shown lately that fat is a compound body, consisting of a substance solid and much like wax, which has been called stearin, and a fluid oil called elain.

Milk is a substance secreted by certain animals for the nourishment of their young. As is well known, milk on standing for a day throws up cream to the surface. Cream has much of the properties of an oil, and when agitated by churning, butter is separated from it. If milk stands until it becomes sour, it separates into a coagulum and a whey. This change may be more completely effected by adding to the milk a small quantity of certain substances, as acids, or rennet, procured by boiling in water the inner coat of the stomach of a calf. The coagulum is thus made more solid, and when pressed and dried it forms cheese.

In animal bodies there are also found several péculiar acids.

The lactic acid is found in sour whey. bines with the earths and alkalies, forming salts called lactates. It resembles much the acetic acid.

The uric acid is found in urine. The substance voided with the urine called gravel, and also those

It com

[ocr errors]

stones formed in the bladder called calculi, are almost entirely composed of uric acid. This acid, however, exists in urine even in its most healthy state.

The amniotic acid is found in the liquor of the amnios of a cow. It separates in white crystals.

The saccho-lactic acid is formed by acting on sugar of milk, or on gum by the nitric acid. It forms salts called saccho-lactates.

The sebacic acid is procured from animal fat. It becomes solid, is of a white colour, with a taste slightly acid.

The Prussic acid has been described, p. under the name of the hydrocyanic acid.

The formic acid is an acid procured from ants.

Animal resins.- Peculiar resins have been found in certain animal substances, as in the bile, ambergris, &c.

Animal sugar is found in milk, also in the urine in certain diseases. It is similar to common sugar.

Blood, when suffered to rest, separates into two parts; the one a coagulum or clot, called the crassamentum ; the other, a fluid called the serum. The crassamentum consists of fibrin mixed with albumen and colouring matter. The colouring part of blood consists of extremely minute globules of a red colour, which float in the serum, and may be seen by the microscope. The red colour of blood has been supposed to be owing to iron which was oxydated by the air in the lungs, but this theory is now rendered questionable.

The serum is composed of albumen, and also contains a small portion of alkali and other substances. It is coagulated by heat, the acids, and alkohol.

Bone is composed of gelatine, another substance which seems to be analogous to cartilage or coa.

gulated albumen, an oil, or marrow, and phosphate and carbonate of lime, besides other matters in minute portions.

Teeth are composed of similar ingredients.

Shells contain a greater proportion of carbonate of lime.

Horns, nails, hoofs, and quills are chiefly gelatine and albumen.

Besides the animal substances above enumerated, there are various matters secreted or formed by certain organs in the body, as saliva, the gastric juice, the bile, the fluid of perspiration, &c., the nature of which is not yet thoroughly known.

The examination of animal substances, called animal chemistry, is one of the most difficult, as well as one of the most important, branches of the science; and a wide field is yet open for research.

When animal bodies are deprived of the vital principle, and are exposed to the air, they undergo a speedy decomposition called putrefaction. By this they are resolved partly into their elementary principles, and some of these form new compounds. The first change is observed by the bodies altering in their colour, losing their elasticity, and by their giving out a very fetid and noxious smell. The greater part, in time, assumes a gaseous form, and nothing remains but a small quantity of earths and salts.

One of the greatest, improvements in chemistry has been that made in its nomenclature, which we owe chiefly to the French chemists. As the former names of many substances differ so entirely from those at present employed, that, without some assistance, many of the old writers on chemistry are not now intelligible to those acquainted only with the modern nomenclature, a list is subjoined

of the terms which most generally occur in old books on this subject, together with those which are now adopted instead of them.

[ocr errors]

Old Names arranged

New Names.
Acetous salts

Acid of vitriol, phlogisticated Sulphureous acid

of alum
of vitriol
of vitriolic

Sulphuric acid
of sulphur
of nitre, phlogisticated Nitrous acid
of nitre, dephlo-

Nitric acid
of saltpetre
of sea salt

Muriatic acid
of chalk

Carbonic acid
of charcoal
mephitic )
of spar or fluor

Fluoric acid
of borax

Boracic acid
of arsenic

Arsenic acid
of tungster
of wolfram

Tungstic acid
of molybdena

Molybdic acid
of apples

Malic acid
of sugar 3

Osalic acid
of lemons

Citric acid of tartar

Tartareous acid of benzoin

- Benzoic acid of galls

Gallic acid of amber

Succinic acid of ants

Formic acid

[ocr errors]


[ocr errors]
[ocr errors]

of phosphorus de-


of phosphorus phlo- } - Phosphorus acid


Phosphoric acid

« PreviousContinue »