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boil the berries in water for two or three hours with constant stirring; the liquors are then strained through cloths in order to separate the woody and other insoluble particles; the clear liquor is boiled down to a syrup, 5 ozs. of alum per gallon added to the syrup, and the mixture carefully evaporated to dryness. For some purposes the mass is left in the pulpy condition.

Sap green is a dark yellowish-green pigment; when dry it breaks with a glossy fracture; it is very transparent, and hence is not used as a body colour, but chiefly as a glazing colour; another use for it is in colouring confectionery and beverages.

It works well as a water-colour, but not as an oil-colour; and fades on exposure to light.

An analysis of sap green made by the author shows it to have the following composition:

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Of the organic constituents a quantity equal to about 29-34 per cent. of the original colour are soluble in alcohol. Its composition and general properties somewhat resemble those of a lake.

MANGANESE GREEN.-This pigment was patented in 1864 by Schad, who prepared it by the following process:14 parts of oxide of manganese, 80 parts of nitrate of barium, and 6 parts of sulphate of barium, are intimately mixed together. The mixture is heated in a crucible in a suitable furnace to a bright red heat until it has assumed a green colour; it is then ground in a mill with water to a fine powder; a small quantity of gum arabic, dextrine, or similar substance, amounting to about 5 per cent. of the original material, is added, and the mass is dried at from 190° to 212° F.; or it may be used in the form of a paste. Instead of the above mixture there may be used one of 24 parts of nitrate of manganese, 46 parts of nitrate of barium, and 30 parts of sulphate of barium. The addition of the gum or dextrine is said to be essential for its stability, a factor which cannot but have an adverse influence on its value as a pigment, for which purpose it has probably not been used. principally of manganate of barium.

It consists

TITANIUM GREEN. This pigment is the ferrocyanide of titanium, prepared by mixing solutions of potassium ferrocyanide and of a titanium salt; the pigment must be dried at a low temperature, as decomposition sets in above 100° C. It has a pale

green colour, and was proposed as a substitute for the arsenical greens; owing to its cost it has never come into use.

ZINC GREEN.-Under this name there is frequently sold greens made in a similar way to the Brunswick greens, by mixing together zinc chrome, Prussian blue, and barytes; such greens possess the advantage that they are not affected by sulphur as much as the Brunswick greens. They are best made in the dry way (see p. 161).

The green lakes and the pigments made from coal-tar colouringmatters will be found described in the chapter on Lakes.

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Blue, as a colour, enters very largely into the decoration of objects, both alone and in combination with other colours, to form a large and very useful series of tints and shades. Although so important as a colour, yet there are few blue pigments; but these possess the merit of being more permanent, and, therefore, more useful than any other group of pigments. The list of blue pigments includes ultramarine (a curious compound of silica, alumina, and soda, which was at one time obtained exclusively from natural sources, but is now mostly prepared artificially), and Prussian blue with its varieties (a most valuable blue, whose base is iron), which are the most predominant blue pigments used. Cobalt is the base of cobalt blue and smalts, while copper forms the basis of several unimportant pigments.

ULTRAMARINE.

Ultramarine is one of the most important pigments possessed by the painter; being used in painting, in printing of all kinds (letterpress, wall-papers, calico), and in bleaching; it is undoubtedly the best blue for the laundry, and in soapmaking it is used to produce the blue mottled soap.

Ultramarine has been known for centuries, but its extended use has only been possible during the last half century. Prior to about 1820 the natural supplies were small, and the processes so expensive that it could only be used by artists who did not find the cost prohibitive; but about the year named, discoveries were made by several chemists, which resulted in ultramarine being made artificially at such a cheap rate that it is the cheapest blue pigment known; consequently, its consumption is now measured by tons.

Natural Ultramarine.—The source of natural ultramarine is a blue mineral, lapis lazuli, found in small quantities in Persia, China, Siberia, and a few other places. This mineral is found in streaks and small patches distributed through an earthy matrix

or gangue, from which it has to be separated by mechanical means. The production of natural ultramarine has declined very much during the last fifty years, it having been displaced by artificial ultramarine; but the mineral is still sought for in fair quantities, for use in the production of inlaid ornamental work, as the peculiar blue colour of the mineral cannot be obtained by other means.

The process of extraction of the pigment from the mineral consists in grinding the mineral to a fine powder, after separating as much of the gangue as possible; it is then mixed with a compound of resin, wax, and linseed oil, and the mixture put into cloths and kneaded under hot water; the colour comes through the cloth into the water, several waters being used; after the working, the waters are placed on one side for the colour to settle. The blue thus obtained varies in shade in the different waters; that which settles out of the first water is the deepest in colour, and the brightest, and is sold as ultramarine; that which comes from the last waters has a blue-grey colour, and is sold as ultramarine ash. After the colour has settled, it is usual to grind it still finer, so that the beauty of the pigment shall be developed as much as possible. No better process for extracting ultramarine has been devised, although it is so tedious and gives such poor results. Very little is now so produced, as the natural variety has been almost replaced in European and other countries by the artificial variety.

The chemical composition and constitution of ultramarine early became the subject of research by chemists, which researches were partly undertaken with a view to its artificial production; for it was recognised that, from the beauty of its colour and its permanent qualities, ultramarine would, if it could be produced cheap enough, have a wide field of use. Several analyses were made by different chemists, but these vary very much, owing, as is probable, to the difficulty of obtaining the pigment quite free from its matrix. Those by Clement and Desormes and by Gmelin, which are, perhaps, the most typical, are here given.

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It is evident that with such discrepancies in the analyses nothing could be satisfactorily inferred as to the chemical composition and constitution of ultramarine, and it is no wonder that none of them led to its artificial production.

Artificial Ultramarine.-Early in the present century, soon after soda began to be produced on the large scale from salt by the Leblanc process, many persons noticed the formation of a substance resembling ultramarine in colour; Tessart and Kuhlmann recorded, in 1814, that they had seen this blue colour in a soda furnace. Vauquelin, on examining it, found it to be a compound of silica, alumina, lime, soda, and sulphur, and showed that it had a similar composition to ultramarine. was recorded that it was formed only when sandstone was used in the construction of the furnace; when bricks were used it was not formed.

It

Guimet, an eminent French manufacturing chemist, studied the production of ultramarine. In 1828 he succeeded in making it on a large scale, and obtained a prize of 6,000 francs, offered by the Société d'Encouragement of France to any one who made ultramarine in a wholesale way. Guimet's process is still used by his successors, but has not been published.

Gmelin also interested himself in the production of ultramarine, and in 1828 he published an elaborate description of his method of making it.

Kottig, the director of the Miessen Porcelain Works also, about the same time, observed the production of ultramarine in his furnaces, and, as the result of his researches, succeeded in making the pigment on a large scale; the Miessen ultramarine was for many years one of the leading brands; the works are now closed.

About 1834 Dr. Leverkus, working by Gmelin's process, started its manufacture in Germany at works which are still in existence.

The great bulk of the ultramarine used is made in Germany; there are two or three works in England, a few in France, and one in America. Several writers have given descriptions, more or less complete, of the process of making ultramarine; but the best and most complete description is that by J. G. Gentele,* and more recently one by Rawlins.+

Varieties of Ultramarine.-There are two principal varieties of artificial ultramarine-1st, sulphate ultramarine, which is of

* Technologiste, vol. xviii., pp. 389-411.
+ Journ. Soc. Chem. Ind., 1887, p. 791.

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