gunpowder is made of alder, willow, or dogwood, exposed to heat in close iron cylinders. The bark is previously removed, as it is this portion alone which crackles when charcoal is united. We will return to gunpowder when treating of POTASH.

The engraver uses charcoal and oil for planishing copper-plates. The manufacturer employs it with iron in making steel; and in refining sugar it is used for removing colour. From its affinity for oxygen, the chemist sometimes selects it as the agent for removing oxygen.-(Vide phosphorus.) In the laboratory and manufactory wood and bone charcoal are employed. In its fine state, as in ivory-black and lamp-black, it forms the basis of black paints, Indian ink, and printer's ink.

Experiment 55.-Place in a crucible, two pieces of wood, with and without bark, cover them with sand, and expose them to a strong heat. After some time, when the vapours cease, charcoal will be found in the crucible. On igniting the two different specimens, that which contains bark will alone crackle.

68. Lowitz of Petersburgh discovered that charcoal removes offensive odours from animal and vegetable substances, and counteracts putrefaction. This constitutes an important feature in domestic economy, for removing colour from vinegar, and odours from meat and water. Small pieces red hot are to be thrown into the vinegar or the vessel containing meat; the water is to be filtered through three or four inches of powdered charcoal, placed on a stratum of fine pebbles and sand, lying on a plate of burnt clay perforated

with holes, (this can be prepared at the pipe-maker's) —such a filter will stand for many years.

In the article on carbonic acid it will be seen that when charcoal is ignited, it forms with the oxygen of the air, carbonic acid, a subject of much importance. (Vide 64.) Carbon unites with sulphur and phosphorus. It combines with nitrogen, forming the basis of prussic acid. United with iron, it forms steel and black-lead, (plumbago,) as will be seen in part third; and with hydrogen it combines in two definite proportions, making carburetted and bicarburetted hydrogen.

QUESTIONS.

248. What is coal principally composed of?

249. How does anthracite differ from common coal ? 250. How is coke prepared?

251. Why is it used on railroads?

252. Describe the two methods for preparing charcoal? 253. Why are the piles of wood covered with earth? 254. Why is it used for covering steam-pipes?

255. Is it affected by fire if confined in close vessels?

256. Relate some of the facts connected with charred wood.

257. What is mixed with charcoal in making gunpowder ? 258. What woods are used in preparing the charcoal? 259. Why is it employed in refining sugar?

260. In obtaining phosphorus, what part does the charcoal play?

261. How would you prepare charcoal on a small scale? 262. Who discovered that it removed offensive odours? 263. How is a charcoal filter prepared?

264. What does it form when ignited?

265. When united with hydrogen what does it form?

CARBURETTED HYDROGEN.

69. This gas is composed of one volume of the vapour of carbon and two of hydrogen. It is colourless and inodorous. It burns with a yellow flame like a candle, and is easily procured from stagnant pools or ditches by

Experiment 56.-Place the mouth of a glass vessel, full of water, in the stagnant pool; stir the bottom with a stick and the gas will ascend into the inverted vessel, this may be called a natural pneumatic trough. This gas is evidently produced, particularly in warm weather, by the action of the hydrogen of water on decaying vegetable matter which parts with its carbon. Carbonic acid is also present from the oxygen of the water uniting with another portion of carbon. The FIRE-DAMP of mines is a gas similar to that of ditches. Against its destructive influence there is the safety-lamp of Sir H. Davy. Without entering minutely into the subject we may easily explain its principle.

Experiment 57.-By holding a piece of fine wire gauze in the flame of a candle it will be seen that though the products of combustion pass through the gauze, THE FLAME DOES NOT; this arises from the metallic gauze cooling the inflammable hydrogen of the tallow below the temperature at which its combustion ensues.

Founded on such experiments, Sir H. Davy surrounded the taper with fine iron or copper gauze, so