production. His experiments were successful; but not till many years after was ultramarine produced on a commercial scale, though now as much as 180,000 cwt. are annually manufactured in Europe, at a mere fraction of the price of the natural product.

The artificial pigment can be made to rival the natural in beauty and softness, at the same time that it admits of a greater variety of shades and tonings. It is manufactured principally in Germany and France, and consists of definite proportions of kaolin or silicate of alumina, calcined sulphate of soda, calcined soda (sulphuret of sodium is a by-product of the manufacture), sulphur, and pulverised charcoal or pit-coal-other ingredients, as gypsum, baryta, &c., being added to tone the colour to special requirements. Different manufacturers adopt different methods and proportions; but the following may be taken as an example of the composition of the artificial pigment: 46.60 silica, 23.30 alumina, 3.83 sulphuric acid, 21.48 soda, 1.06 iron peroxide, with traces of lime, sulphur, and magnesia. Ultramarine is largely employed as a paint, as a pigment for paper-hangings, in calico-printing, for colouring printing-ink, for the bluing of linen, and for imparting blue tints to various fabrics; and is said to be rapidly superseding smalt, litmus, and Berlin blue.

Metallic Pigments.

A great many pigments are prepared from the metals-lead, zinc, copper, cobalt, chromium, arsenic, iron, manganese, mercury, &c.; but as the processes are purely technological, they belong to chemistry rather than geology. The metals, no doubt, belong to the mineral kingdom, and will be treated in other Chapter (XVIII.); but all the reductions, manipulations, and admixtures by which they are converted into colours of unrivalled brilliancy and durability, are matters that lie beyond the domain of the geologist. In illustration, however, of their importance as colour-producers, we may adduce a few examples: From lead we obtained massicot or the yellow oxide, litharge, red-lead, and white-lead; from chromium and lead, chromeyellow, chrome-orange, and chrome-green; from cobalt, smalt or cobalt-blue, cobalt-ultramarine, cobalt-green, and cobaltbronze; from zinc, zinc-white; from copper, Brunswick green, mineral green, emerald green, Bremen green and blue, and the like; from mercury, vermilion; from gold, purple of Cassius; from antimony, orange, Neapolitan yellow, and vermilion-red; from arsenic, realgar and orpiment; and from iron and manganese, various tints of black, red, brown, and yellow. Indeed it is

from the metals that we obtain the majority of our most brilliant and durable pigments; and chemistry is every year inventing new methods and producing new colours-the art of the colourmanufacturer being at once one of the most subtle and successful.

The subject, perhaps, may be rendered more obvious by tabulating the colours and the mineral and metallic sources from which they are derived :

:

White pigments, from lead, zinc, heavy-spar or sulphate of baryta, chalk,

and admixtures.

Yellow pigments, from antimony, lead, arsenic, chromium, chalk, and admixtures.

Orange pigments, from ochre, chromium, lead, chalk, and admixtures. Brown pigments, from umber, Terra di Sienna, manganese, and admix

tures.

Red pigments, from ochre, bole, reddle, chrome, mercury, arsenic, lead, and admixtures.

Black pigments, from iron, manganese, asphalt, coal-tar, and admixtures. Blue pigments, from cobalt, copper, iron, lapis lazuli, potash, soda, and admixtures.

Purple pigments, from gold and tin, and from admixtures.

Green pigments, from copper, chrome, arsenic, potash, and admixtures. Intermediate shades, like compound colours, are all obtained by skilful admixture-the produce, in fact, of the chemist and technologist.

Pastel Pigments.

As already mentioned, pastel pigments for writing, drawing, and marking, consist of colouring matters worked up with pipe-clay, steatite, soap, and various gums, to give them body and consistency. Writing and drawing pencils, drawingchalks, lithographic chalks, and the like, belong to this class of materials. Some of them, like the common black-lead pencils, consist of native mineral substances; others, like the coloured crayons, are manufactured admixtures. Their preparation is wholly technical; we only allude to the minerals which enter into their composition.

Formerly, black-lead pencils were sawn from the finer varieties of graphite, like that of Borrowdale in Cumberland; but now the great majority of those in ordinary use are manufactured from graphite finely triturated, and then compressed into blocks in imitation of the native mineral-the various shades of B, BB, HB, &c., being brought out by admixture and treatment. The Borrowdale mine having been closed for many years, the Keswick pencils, like others in the market, are now chiefly made from the manufactured material. For the composition, modes of occurrence, and other characteristics of

graphite, which is found in the metamorphic rocks of many countries, the reader is referred to Chapter XII.

Coloured Crayons or Drawing-Chalks.-Red, blue, and other tints are chiefly made of fine pastes of pipe-clay, china-clay, or steatite, intimately mixed with earthy or metallic pigments. Some of these so-called chalks, however, are natural products, such as Red chalk, a clay or reddle containing from 15 to 20 per cent of iron peroxide; Brown chalk, a fine variety of umber; Black chalk, a variety of carbonaceous drawing-slate; and French chalk, a variety of steatite or soapstone.

Lithography.

While speaking of chalks and crayons, we may appropriately advert to the limestones fitted for the purposes of Lithography, and which also come under the domain of Economic Geology. Though attempts have been made to utilise some of our own liassic and oolitic limestones, the slabs of the best quality are still obtained from the quarries of Solenhofen, near Munich, where the art of lithography had its birth. There, and throughout Pappenheim, on both sides of the Danube, lithographic slabs of all sizes and qualities can be obtained from the flaggy oolites. Good serviceable stones have usually a yellow or bluish-grey colour, are compact and uniform in texture, and free from veins, flaws, and spots, that would interfere with the delicate lines of the lithographer. The quarrying, dressing, and polishing of lithographic slabs for home use, and their exportation to all parts of the world, has of late years become an important branch of industry in Upper Germany.

Varnishes.

Closely related to the pigments are the varnishes-compounds which are spread over the surface of any body to give it a shining, transparent, and hard coat, capable, more or less, of resisting the action of air and moisture. The great majority of the varnishes employed by cabinetmakers, japanners, tanners, and others, are solutions of gums, resins, and wax in alcohol, turpentine, oils, and the like, and consequently lie beyond the domain of Geology. A few, however, are prepared from amber and asphalt—the former forming a very hard and durable varnish, the latter being the main ingredient in most of the black or Japan varnishes.

II.-DYES.

"Dyeing," says Wagner, "is distinguished from painting by the fact that the pigments are fixed to the animal and vegetable textile fabrics according to certain physico-chemical principles, and are not, as in painting, simply fixed by adhesion to the surface, although painters and artists occasionally use the same pigments. Printing consists in the duplication of coloured patterns, and is a very important part of dyeing. In the art of dyeing, some colouring matters are applied by immersing the tissue to be coloured in the decoction or solution of the pigment. Some substances are applied to the surface of the woven fabric by the intervention of what is termed a 'mordant,' which secures the adhesion, fixing, and permanency of the colours."

The great majority of dyes and dye-stuffs are obtained from the vegetable kingdom; some from the animal; and, till recently, only a few from the mineral. Though these are chiefly of organic origin, the "mordants," or substances employed in fixing or striking their colours, whether in woollen, silk, cotton, or linen, are all, or nearly all, of inorganic origin-such as acetates of iron, lead, and alumina, sulphates of iron and alumina, aluminate of soda, and alum. In this way the art of dyeing comes within the range of Economic Geology. Of recent years, however, the relationship has become more intimate, and by the researches of modern chemistry we now derive from the inorganic world a variety of dyes of unsurpassed beauty and brilliancy. Strange as it may seem, these are chiefly obtained from coal-tar—a dark, dingy, and uninviting by-product of our gas-works. Chemically treated, by a number of ingenious processes this substance yields the aniline or coal-tar colours of commerce-fuchsin, magenta, aniline blue and violet, Manchester yellow, aniline orange and aniline brown, coralline, alizarine, Magdala red, and aniline black. Few triumphs of chemistry have been more marvellous than the production of these beautiful colours—no substances so unlike as a mass of pitchy coal-tar, and the brilliant flush of roseine, mauve, and magenta.

III. DETERGENTS.

Fuller's Earth.

One of the best-known and abundant of mineral detergents is fuller's earth or fuller's clay, so called from its being em

ployed in the fulling of woollens. In composition it is somewhat varied; but all the varieties are soft, unctuous, hydrous silicates of alumina-that of Reigate, from the greensand of Surrey, consisting of 53 silica, II alumina, 24 water, and 9 iron oxide, with traces of magnesia and lime. Good fuller's earth is usually massive, opaque, soft, dull, with a greasy feel and an earthy fracture; scarcely adheres to the tongue; and when placed in water, falls down to an impalpable powder without forming a paste with it. It occurs abundantly in the oolitic and cretaceous systems of England, in beds from one to several feet in thickness, and of a greenish or greyish-green colour. So important at one time was this earth to the woollen manufacture of England, that its exportation was prohibited by Act of Parliament. Its place is now mainly supplied by soap and other chemical detergents, though considerable quantities are said to be still dug and prepared for the fuller in Surrey, Gloucestershire, and Bedfordshire. Besides being used by the fuller, under the names of fuller's earth, Walker's earth or walkerite, and smectite (Gr. smectes, a cleaner) it is also employed in paper-making, and as an addition to artificial ultramarine.

Nowadays the principal detergents, whether employed in woollen, silk, cotton, linen, or leather manufacture, are of chemical preparation-soaps, leys of soda and potash, chlorine, chloride of lime, &c.—and as far as the limes, alkaline salts, and soluble silica (which enters into the composition of some soaps), are concerned, come under the cognisance of Geology. The operations of washing, bleaching, and tanning are all more or less facilitated by preparations obtained wholly, or in part, from the mineral kingdom. The same may be said of sugarrefining, in which lime, gypsum, and baryta are now successfully employed, not only in producing a purer article, but in facilitating the operation.

As explained in the preceding pages, most of the pigments, several of the dyes, and many of the detergents, are obtained either directly or indirectly from the mineral kingdom, and in this way come within the scope of Economic Geology. The elaboration of these substances belongs more especially to chemistry; but to the working geologist is left the discovery of the raw materials, their modes of occurrence, abundance, and the facility with which they can be procured. Many of them have long been known; but some are the results of recent research, and hold out the hope that others may yet reward the skill and industry of the diligent inquirer. The earth is a