Yellow, is one of the seven primitive colours.

The principal article affording a yellow dye, is the Weld, or Dyer's Green-weed ; of the culture of which, the reader will find an account in that article. - See also vol. ii. p. 205.

An excellent yellow dye may likewise be prepared from the flowers of the acacia. These must be gathered, before they be fully blown, and dried in an earthen "Vessel over a moderate fire, till they crisp, or curl up, in the same manner as tea-leaves. The ripe seeds of the same tree are then added in the necessary proportions ; and the whole, when boiled in river-water, with the addition of alum, will impart a yellow colour of any shade required.

In the 61st vol. of the " Philosophical Transactions of the Royal Society, " for 1771, the following receipt for preparing a beautiful yellow dye, is communicated by Mr. Peter Woulfe : Take half an ounce of pulverized indigo, and mix it in a deep glass vessel, with 2 oz. of strong spirit of nitre, previously diluted with 8 oz. of water, to prevent the indigo from taking fire. Let this mixture stand for a week, and then digest it in a sand-heat, for one or two hours; adding .4 oz. of Water. The solution Is now to be filtred : when mixed with water, in the proportion of one part of the former to 4 or 5 of the latter; and, on adding a little alum, it communicates a durable yellow colour. Mr. Woulfk remarks, that none of the tinging matter separates from the water, during the operation of dyeing, except the portion adhering to the cloth ; so that this preparation promises to be of essential service to dyers. He farther states, that cochineal, cudbear, or orchal, and similar colouring substances, when treated in this manner, will also impart a yellow tinge to silk and wool.

The chief yellows used in painting, are Dutch pink, Turbith-mine-ral, King's and Naples yellow : of these we have given a concise account, vol. ii. p. 37; but, as the preparation of the two last-mentioned pigments has not been accurately stated ; we shall subjoin, by way of supplement, a few hints respecting the manner in which they are compounded, for the use of artists.

King's-yelloiw : - Mix 20 parts of pulverized arsenic with one part of the flowers of sulphur: let them be sublimed in a proper vessel, in a sand-heat. When the sublimation is effected, the colour will be found in the upper part of the glass, whence it must be carefully removed, and levigated till it become a fine powder. - This pigment may also be obtained, by subliming orpiment in a similar manner; and it may be rendered of a deeper or lighter colour, by increasing or diminishing the proportion of sulphur.

Naples yellow is prepared by levigating, on a dry stone, 12 oz. of white lead ; 3 oz. of antimony ; 1 oz. of plum ; and a similar quan-tity of sal ammoniac. These ingredients mutt now be exposed, in an open crucible, to a moderate heat for some hours; after which, the fire ought to be increased for a short time; and, at length the mixture should continue for three hours, in a degree of heat sufficiently powerful to keep the crucible red hot. At the expiration of that term, it will acquire a beautiful yellow colour; which may be rendered of a brighter golden shade, by augmenting the proportions of antimony and sal ammoniac.

Yellow pigments of various shades may also be obtained, by triturating flowers of sulphur, or yellow ochre, in different proportions, with a solution of gum in water: and, lastly, the calx of iron, when precipitated by quick-lime, from a solution of green vitriol, has been recommended as a substitute for yellow ochre, in house-painting. - Another method of preparing the celebrated Naples yellow, is that of M. Passery, who makes use of the following ingredients, namely : antimony, 1ib.; lead 1 1/2lb.; alum and common salt, of each 1 oz. - We have inserted this recipe, on the authority of Wiegleb; who simply enumerates the articles here stated, without communicating the process of compounding them.

Yellow Ink may be prepared, by previously dissolving a small portion of alum and gum-arabic in pure water, and then infusing a few grains of dry saffron in the same solution. - It may, likewise, be obtained by slowly boiling 2 oz. of Avignon or French berries in One quart of water, with half an ounce of alum, till one-third of the fluid be evaporated ; when 2 drams of gum-arabic, 1 dram of sugar, and a similar quantity of pulverized alum, are to be dissolved in this liquid : the mixture should then be filtred, and preserved in bottles.

Sympathetic. Yellow Ink, is directed, by Wiegleb, to be prepared in the following manner: - Take a handful of the leaves of common marigold (Calendula officinalis, L.), and macerate them for eight days, or longer, in half a pint of the best distilled vinegar; when the liquid must be separated from the leaves, by expressing them through white linen or cotton, and preferred in a glass bottle carefully stopped. If the desired colour is to be of a pale shade, an additional quantity of water may be added. - Invisible characters may be formed with this liquor on white substances, such as linen, silk or paper ; and the yellow tint will appear on immersing them in the following liquor : - Take a sufficient quantity of violet or daisy flowers ; bruise them in a marble mortar ; add a small portion of water ; express the liquid through white linen, and also preserve it in a glass bottle. - An infusion of turnsol will answer the same purpose.