Phosphorus melts at 111°.45, and boils at 554°. Its vapor is colorless, with a density =

4.328. Exposed to a heat of 140 to 158°, and suddenly cooled, it becomes black; by cooling slowly, it stays transparent and colorless; a moderate cooling gives it the aspect of horn; from black it becomes colorless by fusion, to become black again by cooling.

Mr. Thenard was the first to observe these phenomena. He thought they were common to every kind of phosphorus, but since, he has had occasion to ascertain that such is not the case. He found that phosphorus was susceptible only of those different aspects, even after distilling as often as three or four, and even eight or ten times.

The distillation of phosphorus must be made carefully, and in small quantities, otherwise the facility with which this body burns renders it dangerous.

The phosphorus must be introduced into a small glass retort, fixed in a small furnace. The neck of the retort, which must bo kept warm, communicates with water at about 190°. Heat the phosphorus by degrees till it boils, and continue the heat till the whole is distilled.

The distillation is made below red heat, and does not require even 892°. It always leaves in the retort, a little red powder of oxide of phosphorus.

Solar light colors it red without rendering it opalescent; and this change is effected, not only in the air, but also in vacuum.

Phosphorus kept over mercury, in a glass tube full of oxygen, at a temperature of 80°, and under a pressure of thirty inches, does not absorb oxygen in twenty-four hours; but if the temperature remaining the same, the pressure is diminished, so as to be only two or three inches, the phosphorus begins to be surrounded by a white vapor. It becomes luminous in the dark, it dissolves the gas oxygen by degrees, and forms hypo-phosphoric acid. The less the pressure, the less heat is needed to produce combustion; nevertheless, it will not burn at 41° or below.

If in the above experiment the pressure is increased, the combustion is determined only at a higher temperature.

The addition of more or less quantities of nitrogen, or hydrogen, or carbonic acid, to a given volume of oxygen, produces the same effect. The diminution of pressure is the reason why phosphorus is luminous in the the air, burns slowly in it, and absorbs oxygen to isolate the nitrogen.

Phosphorus is reduced sensibly in vapor, at the ordinary temperature, in all gases which do not attack it.

Phosphorus burns in a mixture of air and oxygen, containing four of oxygen and three of nitrogen, the oxygen being absorbed.

If solid phosphorus acts very slowly on oxygen, it is very different when melted; it immediately absorbs and solidifies the gas, and the result is phosphoric acid. The disengagement of heat is so violent that the eyes cannot bear it.

Besides phosphoric and hypo-phosphoric acids, phosphorus produces two other acids, and one oxide, then it unites with oxygen in five proportions.

It possesses the property of combining with a great many simple bodies, viz., hydrogen, sulphur, selenium, chlorine, bromine, iodine, and all metals. Its union with carbon and nitrogen is a problem. Those that it can make with barium, silicium, fluorine, have not been studied.

As phosphorus has a great action on air, it must be kept in bottles containing no particle of this fluid. For this purpose, boiled water is cooled without the contact of the air, and the phosphorus is introduced into it. The bottle is shut, and kept in a dark place; but, notwithstanding this precaution, phosphorus covers itself with a white crust composed of four of phosphorus and one of water. To preserve it from this alteration, it must be moulded in the form of sticks, and kept in this state in bottles full of water.