18

The greatest care and much experience are required in every stage of the manufacture, in purifying the substances employed, in mixing, in heating at the proper température, and in grinding, washing, and drying the manufactured mass. Fourteen distinct operations are required to produce it, and it would take too much time at this late hour to enter into the details of these processes. I will therefore only attempt to give you a very rough outline of the principal points of the manufacture.

The proportion of materials used, may be as fol-lows :—

White china, clay, or kaolin ....... 50 parts.

Sulphate of soda ................... 19 „

Sulphur............................. 25 „

Charcoal ........................... 12 „

Carbonate of soda .................. 28 „

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These substances are most intimately mixed together and introduced into an earthenware crucible, which is carefully closed and heated at a température of about 500°F. for twelve hours. The température is then gradu-ally raised till it reaches a white heat at the end of 48 hours ; the fire is then removed, and the crucible allowed to cool gradually in the fumace. The mass, as taken outof the crucible, is of a beautiful bright green colour. It is ground, washed, and dried, and then calcined in in an open furnace, to oxidise it ; but as the slightest excess of oxidation spoils the colour, the workman from time to time adds a small amount of sulphur to the mass,

by this means controlling the oxidation. The green mass gradually becomes blue, and is washed and dried, when it is ready for market.

The colouring matter of ultramarine is not well known. It is supposed to be a peculiar sulphite or hyposulphite of soda. The solid matter itself is a double silicate of soda and alumina. What is certainly worth notice is that, although we are ignorant of the true colouring matter of this pigment, we find its composition to be almost identical with that of the natural Lapis lazzdi, which, although very costly, was employed by printers for many centuries. The following analyses will show the similarity of composition :—

Lapis lazuli. Ultramarine

Silica ............

Alumina..................

Soda......................

Potash...................

Iron.....................

Lime ....................

Sulphuric acid ....

Sulphur .................

Chlorine.................

Water....................

Loss.....................

45-40 .... 46-60 31-67 .... 23-30

9-09 .... 21-46 nil .... 1-75

0-52 .... 1.06

3-52 .... 0-02

5-89 .... 3-08

0-95 .... 1-68

0-42 .... trace.

0-12 .... nil 2-42 .... 1-05

100-00 100-00

Artificial ultramarine was discovered by a French chemist and druggist, named Guimet, who kept the pro-cess of its manufacture secret for many years.

LECTURE IV.— DELIVERED TUESDAY, FEBRUARY 28THI, 1871.

QUERCITRON, FUSTIC, PERSIAN BERRIES, WELD, ALOES, TÜRMERIC, ANNATTO, ILIXAN-THINE, LO-KAO, TANNIN MATTERS—GALL NETS, SUMACH, DIVI-DIVI, MYROBALANS, CATECHU.

I shall have the pleasure of devoting the first part of this lecture to some of the most useful and important yellow substances used by dyers and calico-printers, and to one or two other colouring matters which, although scarcely commercially important, are interesting from a scientific point of view.

Among the most valuable of these bodies is quercitron, the bark (from which the epidermis has been removed) of a particular species of oak, called the Quercus nigra or Quercus tinctoria. This tree is indigenous to the United States of America, and is especially found in the forests of Pennsylvania, .Georgia, and in North and South Carolina. A chemist, of the name of Bancroft, first introduced it to theEnglish dyers in the year 1775. The most esteemed qualifies are those imported from Philadelphia, New York, and Baltimore. The bark, after being removed from the tree, is dried, and ground between mill-stones. The value of a sample bears a direct ratio to the fineness of the powder, for the woody fibre of the bark, which contains only a small quantity of colouring principle, is not easily reduced to a fine powder.

M. Chevreul was the first chemist who examined this dye, and he found it to contain a peculiar tannin, which has since reccived the name of quercitannic acid, and a

yellow colouring principle, to which he gave the name of quercitrin, but which has since received the name of quercitric acid from M. Bolley.

M. Chevreul, by boiling quercitron bark in water, and allowing the aqueous solution to stand, obtained fine, laminated crystals, which were gradually deposited, and to which he gave the name of quercitrin.

M. Bolley followed a better process. He treated the bark by alcohol, precipitated the tannin from the alcoholic solution by gélatine, evaporated the alcohol, and obtained the quercitron under the form of colourless crystals. These, under the influence of air or oxidising agents, assume a bright yellow colour. The alkalis give quercitron a brownish tint, but its most characteristic property is to give a greenish-yellow precipitate with chloride of iron, and a beautiful bright yellow precipitate with protochloride and oxymuriate of tin.

M. Rigaud discovered, a few years since, by boiling quercitron with water containing 10 per cent, of sulphuric acid, that it is a glucoside, which décomposés under the influence of the acid into glucose and quercitrin according to the following formulæ :—

Quercitrin. Water. Glucose. Quercitine.

Cs6H40021 + 2 H2O = 2 (C6H12O6) + C24H20011

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