ULTRAMARINE.

i59

of alum in water, both of which discolour and decompose artificial ultra-marine.

In the year 1814 M. Tassant accidentally observed the formation of a blue-coloured substance in the soda furnace at St. Gobain. The substance havingbeen submitted for analysis to Vauquelin, he found it to be identical in com-position with lapis lazuli , and thence argued the possibility of its synthesis.In the year 1824 the Societe d’Encouragement pour l’lndustrie Nationaleoffered a prize of 6000 francs (^*240) for the discovery of a practical methodfor the preparation of ultramarine by artificial means, at a price not exceeding600 francs the kilo. In the year 1827 M. Guimet announced to the Academiedes Sciences that he had succeeded in solving the problem of the manufactureof this substance. The discoverer established a manufactory near Lyons,and had for many years the monopoly of the trade, though the price of 600francs (£24) per kilo, sank to 30 francs. The then Professor of Chemistry atTubingen, M. C. Gmelin, claimed priority of discovery; but after a lengthy,impartial, and painstaking inquiry, there remained no doubt whatever that M.Guimet had claim to the premiums offered.

The manufacture of ultramarine is carried on in France and some parts ofGermany along the Rhine, and in Bavaria. The process there in use was,however, imported from France.

The trade distinguishes four kinds of ultramarine, viz.—(1). The deep andpure blue, as to its colour quite identical with the average of native ultra-marine. (2). Pale blue ultramarine, sometimes with a green tinge, but alwaysa very brilliant pigment. (3). Ultramarines of a violet or rose hue. (4). Greenultramarine, of a dull appearance. As many as thirty-six different varieties ofultramarine, gradually verging from perfectly pure blue to pure green, may bemet with.

Ultramarine, artificial as well as native, is decomposed by excess of hydro-chloric acid; sulphuretted hydrogen is given off, leaving a milky and gelati-nous liquid, which runs turbid through filtering-paper, owing to the very finelydivided state of the sulphur, the quantity of which is far larger in artificialultramarine than in the native product. Ultramarine is not affeCted by air andsun-light, withstands washing with soap and alkalies, and is fixed upontissues by means of albumen. There exists no proof whatever as to theorigin of the blue colour of this pigment. Notwithstanding the number ofanalyses made of the native as well as of the artificial product, no rationalecan be given of the blue colouration from the composition of the material,while the question arises whether or not the component substances are modifiedas soon as acids are caused to aCt upon them.

The manufacture of ultramarine on the large scale requires a great deal ofskilful management, and more than ordinary taCt, in regulating the heat, whichis always higher than full red-heat. The material called green ultramarine isthe result of incomplete ignition.

Ultramarine is a substance not subject to wilful adulteration to any greatextent; it is sometimes customary to dilute the pigment with whites, such assulphate of baryta and lime. Ultramarine of good quality exhibits anextremely deep blue powder, which imparts its beautiful colour very readilyto other substances with which it is mixed. It is used in printing, and is fixedby means of albumen and steam.