VERMILION, is Ethiop's mineral, heated red-hot, and sublimed. It is e bi-sulphuret of mercury. In a cake it is cinnabar, but, in powder, vermilion,.
Chinese Vermilion.—Take quicksilver and sulphur, in the proportion of sixteen parts 'of the former, to four of the latter. After powdering the sulphur, place the two ingredients in an earthen ,jar, the outside of which, to exclude the air, must be plastered with mud and salt, to the thickness of three inches and a half; place an iron cover on the mouth of the jar, and let it be kept constantly moist. Place the jar in an oven, early in the morning, and at the same hour on the next morning extinguish the fire ; at noon take it out of the oven, and, when cold, break the jar in pieces, and take out the contents. Pick out the dross, and then reduce the rest to a fine powder : let this be poured into a large jar full of water. After a time, a thin coating will be found on the surflice of the water, which must be skimmed off, and a por tion of the water let off; in a short time this process must be repeated, and the third time let all the water be drained off. The sediment is then exposed to dry, and taken out in cakes.
The humid process of Kirehoff has of late years been so much improved, as to furnish a vermilion quite equal in bril liancy to the Chinese. The following pro cess has been recommended : Mercury is triturated for several hours with sulphur, in the cold, till a perfect ethiops is form ed; potash ley is then added, and the trituration is continued for some time. The mixture is now heated in iron ves sels, with constant stirring at first, but afterwards only from time to time. The temperature must be kept up as steadily as possible at 180° Fehr., adding fresh supplies of water as it evaporates. When the mixture which was black, becomes, at the end of some hours, brown-red, the greatest caution is requisite, to prevent the temperature from being raised above 114°, and to preserve the mixture quite liquid, while the compound of sulphur and mercury should always be pulveru lent. The color becomes red, and bright ens in its hue, often with surprising ra pidity. When the tint is nearly fine, the process should be continued at a gentler heat, during some hours. Finally, the
vermilion is to be elutriated, in order to separate any particles of running mercu ry. The three ingredients should be very pure. The proportion of product varies with the constituents. (See MEncuay.) VIBRATION. Reciprocal motion. In music, that regular reciprocal motion of a body, which, suspended or stretched between two fixed points, swings or shakes to and fro. The vibrations of chords are the source of the different tones they emit. If two strings or chords of a musical instrument merely differ in length, their tones, that is, the number of vibrations they make in equal times, are in the reverse ratio of their lengths. If they differ in their diameters only, their sounds will be in the inverse ratio of their diameters. To measure the tension of strings, let us conceive them stretched by weights attached to their ends; then their sounds will be in the direct ratio of the square roots of the weights stretching them; that is, the pitch of a string stretched by a weight equal to 4 will be an octave above the pitch of a string stretched by a weight 1.
Vibration in mechanics is the recipro cating motion of a body, as of a pendu lum, a musical chord, or elastic plate. The term oscillation is, however, more frequently used to denote a slow recipro cating motion, as that of the pendulum which is produced by the action of gravi ty on the whole mass of the body ; while vibration is generally confined to a motion with quick reciprocations, as that of a sonorous body, and which proceeds from the reciprocal action of the molecules of the body on each other when their state of equilibrium has been disturbed. Metallic rods or glass tubes may vibrate longitudinally like stretched chords. In this case they divide themselves sponta neously into several parts, which vibrate in unison ; and are separated by nodes, or parts which remain at rest. The extreme parts are shorter than the others which are all of equal length ; but the vibrations of all the parts are synchronous. This sort of vibration may he induced in a slip or tube of glass, by holding it between the fingers, in the middle, and rubbing it longitudinally with a piece of moist cloth„ when it will emit a very acute sound.