/6 PROOFS OF THE PROPERTIES OF MERCURY.

tinued until the mixture begins to change from its original blackcolour to a brown, which usually happens when a large part ofthe fluid is evaporated; it then passes very rapidly to a red. Nomore water is now to be added, but the trituration is to be con-tinued. When the mass has acquired the consistence of a jelly,the colour increases in brightness, with an incredible degree ofquickness. The instant it has acquired its utmost beauty, theheat must be withdrawn, otherwise its brilliancy will be impaired,and the red will pass to a brown colour. This red powder isalso sulphuret of mercury or cinnabar.

Remarks. ..Until lately cinnabar was considered to be a com-pound of the red oxid of mercury and sulphur, but Mr. Prousthas shown that it is composed of about 15 parts of sulphur, and85 of mercury, and that it differs from the preceding preparationin not containing hidrogen.

Count de Moussin Pouschin has discovered that its passing toa brown colour may be prevented by taking it from the fire assoon as it has acquired a tolerable red colour, and placing it fortwo or three days in a gentle heat, taking care to add a few dropsof water, and to agitate the mixture from time to time. Duringthis exposure the red colour gradually improves, and at lastbecomes excellent. He discovered also that, when the sulphuretis exposed to a strong heat, it becomes instantly brown, and thenpasses to a dark violet > when taken from the fire it acquires abeautiful carmine red.

Experiment V.

Preparation of pkosphuret of mercury.

Put into a Florence flask equal parts of red oxid of mercury,and phosphorus; add one part of water, and place the flaskon a sand-bath, taking care to shake it frequently, and not toremove it from the bath too early ; it will soon become blackish,and in that state the mercury remains united to the phosphorus.