of copper, prepared by precipitating solutions of copper with the carbonates of potash or soda in the same way as blue verditer is made. It has a pale tint of a somewhat yellow tone of green. As a pigment it has no great use, and has become nearly obsolete; it is not permanent, either as an oil or a water colour. Green verditer has also been known as "British verdigris,” and its preparation under this name has been patented.

BREMEN GREEN. This is of a pale green tint, prepared in the same way as Bremen blue, except that the final blueing is omitted. Like green verditer it is essentially a basic carbonate of copper. Its use as a pigment has become obsolete.

PROPERTIES OF THE COPPER GREENS.-With one or two exceptions, the copper greens are by no means satisfactory pigments; their colour is but pale and not brilliant, except emerald-green and the natural mineral green. Their covering power is also deficient; they mix with either oil or water. They are not permanent, as exposure to light and air causes them to fade, while sulphuretted hydrogen and sulphur compounds cause them to go black, owing to the formation of the black sulphide of copper; hence they cannot be mixed with any pigments containing sulphur-such as cadmium yellow, King's yellow, ultramarine, &c. Strongly alkaline bodies, such as lime, change their colour to a blue.

Heat decomposes all the copper greens, the acid portioncarbonic, acetic or arsenious-being volatilised, and a black residue of oxide of copper being left behind.

They are all soluble in acids, some with effervescence, indicating the presence of a carbonate; the solutions have a blue colour, to which ammonia imparts a characteristic deep blue tint; on adding caustic soda a blue precipitate is obtained, which, on boiling, turns black. Sulphuretted hydrogen gas passed through the solutions throws down a black precipitate of the sulphide, which is soluble in nitric acid to a blue solution.

TERRE VERTE.

Terre verte is the name given to green pigments of an earthy character, found naturally in various places; in some cases, the pigment has been named after the place where it was found, as 66 Verona green," ," "Verona earth," &c. These natural greens are usually of a pale greyish-green tint, and are only useful on account of their permanence. Deposits of green earth are found in many places, but only the deep bright samples are usable as pigments. The places where the best qualities of terre verte are found are

the Mendip Hills, as also many localities in France, Italy, and Cyprus.

Terre verte is found in masses of a more or less compact character; some varieties are soft and easily powdered, others are harder and more vitreous in appearance. For use as a pigment, the mineral is ground up as fine as possible; sometimes it is levigated.

Although varying somewhat, as might be expected in earthy pigments from various sources, yet there is a certain amount of resemblance between different samples of terre verte, as shown by the few analyses of this pigment available. Berthier gives

the following analysis of terre verte, the source of which is not stated:

This is not a very satisfactory analysis; of what does the 4 per cent. of unaccounted for material consist?

A sample of terre verte from Cyprus, analysed by Klaproth, gave the following figures :

A sample of terre verte from the neighbourhood of Rome was examined by the author, and found to have the following composition:

This sample was very hard, and had a conchoidal fracture, a waxy lustre, and a soapy feel. Acids had but slight action on it. It was evidently a specimen of the mineral bronzite, which is essentially a ferrous magnesium silicate.

As a

Terre verte is of a pale bluish-grey tint, and has no great colouring power or body, being somewhat transparent; it mixes well with either oil or water, and is perfectly permanent, being unaffected by any length of exposure to light and air; it is not altered by sulphur or sulphureous gases in any way. pigment terre verte has been used from very early times, being one of the best greens available to the early painters. Heat turns the colour of terre verte to a reddish-brown, the change being similar in nature to that which takes place when the ochres are heated.

Sometimes greens having a copper base are offered as terre vertes; these are not permanent.

Cobalt

COBALT GREEN.

green, Rinman's green, Zinc green is a compound of the oxides of zinc and cobalt, having an analogous composition to cobalt blue and being prepared in a similar manner. Preparation of Cobalt Green.

prepared in several ways.

Cobalt green

can be

(a) Sulphate of cobalt in solution is mixed with zinc oxide into a paste; this is then dried and exposed to a red heat in a muffle furnace until the desired green tint has been developed, which will take from three to four hours. The tint of colour will depend upon the proportions of the cobalt salt and zinc oxide used; 1 lb. of cobalt sulphate to 5 lbs. of zinc oxide will give a deep green; with twice as much zinc oxide a grass green is obtained, while if the proportions are 1 lb. of cobalt sulphate to 20 lbs. of zinc oxide a fine bluish-green is obtained, which forms a fair substitute for emerald-green.

(b) Instead of the sulphate, the nitrate of cobalt may be used. 1 lb. of cobalt nitrate is mixed with 2 to 5 lbs. of zinc oxide according to the depth of colour required, the mixture is kept at a bright red heat in a muffle furnace for a few hours until the green has been fully developed; it is then ground with water, and dried. The cobalt salt must be free from metallic impurities, such as iron, alumina, or tin.

The principal difficulty in these two processes is that of ensuring a thorough mixture of the cobalt and zinc compounds; if this is not properly done the green which is formed will not be

of a uniform tint throughout the mass; there will be dark and light places. The following processes avoid this difficulty by mixing solutions of the two metallic salts, thereby ensuring perfect admixture, then precipitating the oxides from the solution and finishing as in the above processes :

(c) 1 lb. of nitrate of cobalt or lb. of the chloride of cobalt and 6 lbs. of sulphate of zinc are dissolved in 7 gallons of water; a solution of carbonate of soda is then added as long as a precipitate falls; the mixture filtered, and the precipitate of hydroxides of cobalt and zinc so obtained washed, dried, and heated as before. By varying the proportions between the zinc and cobalt salts the depth of colour of the resulting green can be varied to a great extent.

(d) Instead of using the carbonate of soda to precipitate the solution of zinc and cobalt, there may be used either the phosphate or the arseniate of soda. Wagner states that the resulting green is purer, brighter, and less dense. The greens made in this way will contain phosphoric acid, which will give the greens a rather bluer tint.

Cobalt green has a bright green colour of a slightly yellow hue. It is perfectly permanent when exposed to light and air, and is on that account a useful pigment. It can be mixed with all other pigments without being affected by them or altering them in any way. It is unacted upon by acids in the dilute state; but strong acids decompose it, forming a blue solution. Alkalies have no action on it.

Wagner gives the following analyses of cobalt green made by various processes :

Owing to its cost cobalt green is not much used.

Should it be possible to find a cheap source of cobalt this green might come into more general use, as its permanent qualities would give it superiority over many of the other greens.

Besides the greens described above many others have been used on a small scale, some are still used for special purposes, and others have been described by various chemists, but whether they

have ever been used on a practical scale is doubtful; these will be briefly described.

BRIGHTON GREEN is the name given to a pigment made by grinding together in the dry condition 7 lbs. of copper sulphate, 3 lbs. of acetate of lead, and 24 lbs. of whiting; during the grinding chemical decomposition sets in, resulting in the formation of a basic acetate of lead. It was a pigment of no great depth of colour or permanency.

DOUGLAS GREEN.—Mr. Thomas Douglas has described in the Chemical News, vol. xl., p. 59, a green prepared from barium chromate. The latter compound, prepared in the usual way by mixing solutions of barium chloride and potassium chromate, is mixed with 20 per cent. of its weight of strong sulphuric acid, which partially decomposes it, forming a mixture of barium chromate, chromic acid, and barium sulphate; the mixture is dried and then calcined at a bright red heat in a crucible; the chromic acid is thereby decomposed into the green oxide of chromium, which, being disseminated throughout the mass of barium sulphate and chromate, colours it green, forming a pigment possessing considerable body and permanency. Nothing definite is known as to its having been used as a pigment.

CHINESE GREEN or LOKAO.—This is a green pigment, as yet but little used, made from the juice of various Chinese species of buckthorn trees by extracting the juice from the berries by pressure, mixing this with alum, &c., and drying. It comes into commerce in the form of bluish-green slabs, which are easy to break, but somewhat difficult to powder. Chinese green contains from 27 to 47 per cent. of mineral matter, principally lime and alumina, and, probably, consists of the lake formed by the combination of those bases with the colouring principle of the juice from the buckthorn berries, named by Kayser lokaonic acid, C42 H48 O2 According to the same authority, the colouring principle consists of a glucose, which he calls lokaose, to which he assigns the formula C6 H12 06, and lokanic acid, a body having the composition C33 H36 021 The colouring principle has also received the name lokain and the formula C28 H34 017

27.

SAP GREEN.-This pigment is prepared from buckthorn berries. Two methods are adopted in its preparation. In one the berries are allowed to ferment slightly by placing them in a warm place for a few days; they are then pressed, the juice collected, and alum added in the proportion of from an ounce to 1 ounce per pound; the mixture is then boiled down and evaporated to dryness at the boiling heat. Another plan is to