XV. Experiments to show the Nature of Aurum Mosaicum. By Mr. Peter Woulfe, F.R.S. p. 114 (1771)

The Philosophical Transactions of the Royal Society of London, For their commencement, in 1665, to the year 1800: Abridged, with notes and biographic illustrations by Charles Hutton, LL.D. F.R.S. George Shaw, M.D. F.R.S. F.L.S. Richard Pearson, M.D. F.S.A. VOL XIII From 1770 to 1776. London: Printed by and for C. And R. Baldwin, New Bridge-Street, Blackfriars. 1809


*The mixture recommended for the preparation of aurum mosaicum by Mr. W. is as follows: tin, 12 oz; sulphur 7 oz.; sal ammoniac, 3 oz.; mercury, 3 oz, From this mixture (varied from the formula in the Lond. Pharmacopoeia of that day) he obtained 17½ oz. of aurum mosaicum; but Mr. W. showed by other experiments, that mosaic gold could be prepared without employing either mercury or sal ammoniac. The celebrated French chemist, Mons. Pelletier, has since shown that aurum mosaicum may be obtained by a very short and simple process; viz. by subjecting to a proper degree of heat equal parts of oxyd of tin and sulphur; thus demonstrating its composition, viz. that it is a sulphuretted oxyd of tin.
After describing various processes (with observations thereon) for making aurum mosaicum (sulphuretted oxyd of tin) which in the present improved state of chemical knowledge it would be useless to retain in these Abridgments, Mr. W. subjoins the following account of an apparatus for making aurum mosaicum in the cheapest manner.

A glass vessel cannot be used for this operation more than once, because it is necessary to break it to get out the aurum mosaicum. The following utensil may be employed a great number of times, and save the expence of glass. Take a black lead crucible, N° 60; bore a round hole in its bottom about 3 inches diameter; and saw off an inch of its upper edge; if it has a lip, get a round piece of burnt clay, of an inch thick or rather more, to fit exactly into this edge; the composition, which is used for making paving-tiles, answers very In order to make use of this apparatus, fit the round piece of burnt clay to the inner edge of the crucible, by means of some loam softened with glue, and dry it slowly; then turn it upside down, and lay it in a proper furnace on 2 iron bars. The mixture* for the aurum mosaicum is to be put in through the round hole at top, and then covered with an aludel and luted; this serves to collect the flowers and the sublimate which rises. The fire is to be made under and all round the crucible. 1 1 lb. Troy of aurum mosaicum may be made here at a time; and when the operation is over, the bottom or round piece of burnt clay will easily come out widi the aurum mosaicum. A large crucible may be made use of, if a larger quantity be required to be made at once. The operation cannot fail of success, provided the fire be made of a sufficient strength, and of an equal degree from 1,he bottom to the top of the crucible, which is easily done in a good furnace. The operation is finished in 8 hours, unless the volatile liver is wanted. White, arsenic, digested with a solution of tin in the acid of salt, becomes soon black; it hereby regains its phlogiston, and is reduced to the taste of regulus of arsenic, and will by this means readily combine with copper, and other metallic substances; which it would not do without the help of phlogistic substances! This is the most easy and ready way of reducing arsenic to its metallic form: the arsenic may be deprived of the solution of tin, which adheres to it, by washing it with water. It is to be dried slowly, for otherwise it is apt to catch fire.

Then follows an account of a method of dying wool and silk, of a yellow colour, with indigo; and also with several other blue and red colouring substances.

The Saxon blues have been known for some time; and are made by dissolving indigo in oil of vitriol, by which means the indigo becomes of a much more lively colour, and is extended to such a degree, that it will go very far in dying.

A receipt for making the best Saxon blue will, Mr. W. doubts not, be agreeable to many; he therefore gives the following, which produces a very fine colour, and never fails of success. Mix ξ1 of the best powdered indigo, with ξ4 of oil of vitriol, in a glass body or matrass: and digest it for one hour with the heat of boiling water, shaking the mixture at different times; then add ξ12 of water to it, and stir the whole well, and when cold, filter it. This produces a very rich deep colour; if a paler blue be required, it may be obtained by the addition of more water. The heat of boiling water is sufficient for this operation, and can never spoil the colour; whereas a sand heat, which is commonly used for this purpose, is often found to damage the colour, from its uncertain heat.

Indigo, which has been digested with a large quantity of spirit of wine, and then dried, will produce a finer colour than the former, if treated in the same manner, with oil of vitriol. No one, that he knew of, had before made use of the acid of nitre, instead of the acid of vitriol; and it is by means of the former that the yellow colour is obtained: it was nevertheless natural to use it, on account of its known property of making yellow spots, when dropped on any coloured cloth. The acid of salt does not dissolve indigo, and therefore is of no use in dying.

Mr. W. further communicates a receipt for making the yellow dye.

Take ξ½ of powdered indigo, and mix it in a high glass vessel, with ξ2 of strong spirit of nitre, previously diluted with ξ8 of water; let the mixture stand for a week, and then digest it in a sand heat for an hour or more, and add ξ4 more of water to it; filter the solution, which will be of fine yellow colour. Strong spirit of nitre is liable to set fire to indigo; and it is on that account that it was diluted with water, as well as to hinder its frothing up. ξ2½ of strong spirit of nitre will set fire to ξ½ indigo; but, if it be highly concentrated, a less quantity will suffice. If the indigo be digested 24 hours after the spirit of nitre is poured on it, it will froth and boil over; but after standing a week or less, it has not that property.

One part of the solution of indigo in the acid of nitre, mixed with 4 or 5 parts of water, will dye silk or cloth of the palest yellow colour, or of any shade to the deepest, and that by letting them boil more or less in the colour. The addition of alum is useful, as it makes the colour more lasting; according as the solution boils away, more water must be added. None of the colour in the operation separates from the water, but what adheres to the silk or cloth; of consequence this colour goes far in dying. Cochineal, Dutch litmus, orchel, cudbear, and many other colouring substances treated in this manner, will all dye silk, and wool of a yellow colour. The indigo which remains undissolved in making Saxon blue, and is collected by filtration, if digested with spirit of nitre, dyes silk and wool of all shades of brown inclining to a yellow. Cloth and silk may be dyed green with indigo; but they must first be boiled in the yellow dye, and then in the blue.

Ei kommentteja :