Jeudi 28 juillet 2011

The substance used for pencils

Charcoal is fixed in the fire, no degree of being able to produce any change on it, so long as the air is excluded.
Obs. When newly made, it will absorb about 90 times its own bulk of ammoniacal gas, and certain, but less quantities, of any other gaseous substance.
148. It attracts from the air a quantity of water, which it strongly retains. The powder of fresh charcoal, is strongly disposed to unite to the odorous particles of bodies and the coloring matter of vegetables : hence it may be employed to correct the bad smell of corrupted water, of oiled silk bags, of ill conditioned ulcers, and of decayed teeth, when used as a tooth powder: it is employed to deprive vegetable infusions and other substances used in chemistry, of their colour, and for giving mellowness and maturity to newly distilled spirits.
Obs. Its principal use is as fuel, but it always ought to be remembered, ti at the gas which arises from burning charcoal, is the most insidious and deleterious that can be inhaled.
149. Charcoal when perfectly freed from saline and earthy matters, may be considered as pure carbon, differing from the diamond only in form and colour.
150. Charcoal has the quality of rendering putrid substances sweet, and preserving animal substances from putrefaction.
Ilius. 1. Let putrid water, as from a ditch, be passed through a few inches in depth, of pulverized charcoal. It will come through perfectly sweet, and fit to drink.
2. Finely powdered charcoal is of peculiar efficacy as a dentrifice, its particles being sufficiently hard to remove the concretions from the teeth, without hurting the enamel, while at the same time it destroys the fetor arising from a carious tooth.
3. If meat that is a little tainted be rubbed with fine charcoal, it becomes sweet. Fresh meat may be preserved for a considerable time, if surrounded with pulverized charcoal.
For all the above purposes, it is understood that the charcoal is to be fresh prepared, finely pulverized, and perfectly dry.
151. Neither air nor moisture affect charcoal at ordinary temperatures.
li/us. It is stated by Mr. Watson, that the beams of the theatre at He.culaneum, which were converted into charcoal above 1700 years ago, are still as entire, as if this event had happened only yesterday. It is also said, that there still exists charcoal made of corn in the days of Caesar, which is in so perfect a state, that the grains of wheat can be distinguished from those of rye.
152. Carbon unites to several substances, forming * class of compounds called carburets.
Illus. The substance used for pencils, and improperly callled black lead, is a carburet of iron, and contains about ten parts of carbon to one of iron. The name black lead was given it long before its real composition was known. Steel is a carburet of iron, or a compound of iron and diamond ; hence its hardness. The conversion of iron into steel depends on a quantity of carbon which it absorbs from the charcoal when it is heated. Case hardening is the superficial conversion of the surface "of iron into steel, by heating it in contact with animal carbon in close vessels. Bar iron is converted into steel, in the same way; only that powdered charcoal is the substauce in which it is imbedded.


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Par qida23 - 0 commentaire(s)le 28 juillet 2011

If you pound it and wash away

 In the natural state, phosphorus is found combined'with lime in the form of an acid, forming phosphate of lime, which is the composition of bones.
138. Sulphur is a well 'known substance of a yellow colour, without much taste and without smell unless it is heated or rubbed. So far as is known, it is a simple body. It exists in nature in great abundance, being found in the animal, vegetable, and mineral kingdoms : but chiefly in the latter. .
Obs. The sulphur of commerce is chiefly dug out of the earth in volcanic countries, or in the craters of extinct volcanoes. It is deposited in these places by sublimation, being brought up by the heat from the depths below, where it existed in combination with metallic substances. It is also obtained, of an inferior quality, during the process of refining coppor ore.
139- When sulphur is heated to a little above the temperature of boiling water, it melts and becomes completely fluid. But it is a singular fact, that if the heat be raised much above this, it again becomes solid, and becomes fluid again as the temperature is reduced.
If after it is melted, it is safiered to cool, it shoots into crystals.
140. When sulphur is in complete fusion, if it is poured into.water it becomes soft and tenacious like wax.
Obs. in this slate it is made use of to take impressions from medals and engraved stones, and as it soon becomes hard, it will retain tni impression for any length of time.
141. When sulphur is exposed to a beat of about 300 degrees, it sublimes, or is converted into vapor.
Obs. In this stale it is called Jlawers of sulphur, and differs from brimstone only in being more pure, and in a state of minute division
142. Sulphur combines with the earths, alkalies, and metals, and forms a class of compounds called sulphurets.
143. It unites to oxygen in two proportions and forms two acids, the sulphurous and sulphuric : see acids.
144. It unites with hydrogen, forming sulphuretted hydrogen This substance is extricated from animal substances during their decomposition, and is chiefly the cause of the disagreeable smell.
Carbon is a constituent of all vegetable and animal substances. When perfectly pure and crystallized, it constitutes the most costly of all substances, the diamond.
Obs. If carbon could be crystallized by art, the diamond would immediately lose a great part of its value. But as yet, this has been effected in the labratory of nature alone.
146. The method of making charcoal is by submitting wood, to a red heat, having it covered from the contact of the air.
Example. Expose wood of any kind, stripped of its bark, to a red heat in a close vessel, till vapors cease to issue, and you obtain a black, opake, brittle substance, easily reduced to powder, and without taste or smell. This is charcoal.
Obs. If you pound it and wash away the salts it may contain by dilute muriatic acid, and afterwards, by repeated effusions of cold water, and then dry it at a low red heat, you obtain it sufficiently pure for experiment. Common charcoal dried in an oven will do, where great nicety is not required.


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Par qida23 - 0 commentaire(s)le 28 juillet 2011
Mercredi 27 juillet 2011

When gum is submitted to destructive

By subjecting different vegetable substances to ultimate analysis, it has been ascertained that the products which result from the different combinations of oxygen and hydrogen, are as follows :
A vegetable substance is always acid where the oxygen which it contains is to the hydrogen in a proportion greater than is necessary to form water, or where there is excess of ,oxygen.
A vegetable substance is resinous, oily, or alcoholic, where the oxygen is to the hydrogen, in a less proportion than in water, or where there is excess of hydrogen.
A vegetable substance is neither acid nor resinons, but saccharine, mucilaginous, &c. where the oxygen and hydrogen are in the same relative proportion as in water, or where there is no excess of either.
Obs. In addition to the oxygen and hydrogen, there is in resin, oil, alcohol, sugar, and mucilage, a quantity of carbon.
530. jThe ingredients of plants are distinct substances, formed by their secreting organs, and separable from each other without destructive distillation.
531. They are separated by certain solvents which have the power of dissolving some, but not the others. Thus water dissolves gum, but not resin ; while alcohol will take up the resin and leave the gu.-u, &c.
Obs. The solvents made use of for separating the ingredients of vegetables, are hot aud cold water, alcohol, ether, and some of the acids.
2. The following are the principal ingredients, or what are called the proximate principles of vegetables. Some account of the most important among them will be given.
1. Gum. 9. Fixed oil.
2. Sugar. ,10. VolatUe oil.
3. Starch. 11. Camphor.
4. Gluten. 12. Resins.
5 Extractive and Lignin 13. Narcotic principle.
6. Tannin. 14. Bituminous substances.
7. Colouring matter, 15. Vegetable acids.
8. Wax.
532. Gum. Gum Arabic may be taken as a specimen of pure gum. It dissolves in water forming a viscid solution, or mucilage from which it may be obtained in its original state by evaporation. It is insoluble in alcohol, which therefore causes a white precipitate in its aqueous solution.
Obs. 1. Gum is decomposed by sulphuric and nitric acids : the former produces water, acetous acid, and charcoal; tbe latter among other products converts a portion of the gum into a white acid substance, called mucous acid.
2. When gum is submitted to destructive distillation it affords carbonic acid, and carburetted hydrogen, empyreumatic oil, water, and a quantity of impure acetic acid.)
Par qida23 - 1 commentaire(s)le 27 juillet 2011

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