For an hundred pounds of silk, twenty pounds of Aleppo galls, in powder, are to be boiled an hour in a sufficient quan tity of water. The bath is then left to settle till the galls have fallen to the bot tom, when they are taken out, and two pounds and a half of English vitriol of iron, twelve pounds of iron filings, and twenty pounds of gum, are put into a copper cullender with two handles, and immersed in the bath ; the cullender is supported by sticks, that it may not touch the bottom, and an hour is allowed for dins lying the gum, which is occasionally stirred. If all the gum be dissolved in that time, three or four pounds more may be added. The cullender is only re moved during the dyeing, and is put in again after it : the copper is kept hot the whole time, but not suffered to boil : the silk is galled with one-third of Aleppo gaits, and left in the liquor six hours the first time, and twelve the second. The rest of the process is conducted in the common method. The gum is useful to keep the dye suspended in the liquor ; but it is probable a smaller quantity might answer As galls are expensive, the following method has been used to lessen their con sumption. The silk, after being boiled and washed in the river, is prepared by immersing it in a strong decoction of walnut peels till the colour is exhausted : it is then wrung, dried, and again washed in the river ; after which it is left in a so lution of two ounces of verdigrise for eve ry pound of silk, in cold water, for two hours, and then clipped in a strong decoc tion of logwood, which gives it a blue ground ; it is then wrung out, dried, and washed in the river. The black bath for it is prepared by macerating two pounds of galls and three of sumach in twenty five gallons of water, over a slow fire, for twelve hours ; after straining, three pounds of sulphate of iron and as much gum arabic are dissolved in it. In this solution the silk is dipped at two different times, left two hours in the bath each time, and aired and dried after each dip ping ; it is then beetled twice at the river, dipped again, and left in the bath four or five hours ; drained, dried, and again beetled twice, as before. The heat of the bath must not exceed 122 Fahrenheit. Before each of the last dippings, half a pound of sulphate of iron, and as much gum arabic, should be added. Some think that the galls are only added to increase the weight, and that the sumach is sufficient for the dye.
Of dyeing Cotton and Linen black.
Cotton and linen do not take a black that will resist soap. The weakness of their affinity for iron renders a'solution of it necessary in dyeing them in some acid, to which it has less attraction than to the sulphuric. This solution is pre pared with iron and vinegar, or alegar from small beer or fermented worts, ac cording as the country where the process it carried on affords them cheapest. (Py rolignous acid, or the acid liquor pro cured in distilling spirits of turpentine, has also been used for the same purpose with success.) Pieces of old iron are thrown into the acid. liquor, and they are allowed to remain in it six weeks or two months before it is used, that it may he fully saturated with the iron. This solution is called iron liquor in this country.
The process for dyeing linen and cot ton thread black at Rouen is the follow ing. It is first dyed sky blue ; then wrung
out and dried, (a deep blue is thought to be better ;) it is next galled, using four ounces of galls to every pound of thread, and leaving them twenty-four hours in the gall liquor : after which they are wrung out and dried again. About five quarts of the iron liquor are then poured into a tub, in which the thread is worked by hand, pound by pound, for a quarter of an hour, and then wrung out and aired. This operation is repeated twice, adding each time a fresh quantity of the iron liquor, which should be care fully scummed ; after this the thread is again aired, wrung out, washed at the river, and dried.
The thread receives the colour by im mersion in the following bath: A pound of alder bark for every pound of thread is boiled an hour, in a sufficient quantity of water ; about half the bath that served for the galling, and half as much sumach as alder bark, are then added, and the whole boiled together for two hours, and strained through a sieve. When the li quor is cold, the thread is put into it on sticks, and worked pound by pound, air ing it from time to time ; it is then let down into the bath again, left in it twenty four hours, wrung out, and dried. To soften this thread, it is usual to soak and work it in the remains of a weld bath, that has been used for other colours, adding to it a little logwood.
At Manchester, the method used is, to first gall the stuff with galls or sumach, then to dye it in the iron liquor, and af terwards to dip it in a decoction of log wood and a little verdigrise. This process is repeated till a deep black is obtained. It is necessary to wash and dry after each operation. The iron liquor for this pro cess is frequently composed of infusion of alder-bark and iron.
M. Guldiche recommends highly the following solution of iron for dyeing linen and cotton. A pound of rice is to be boiled in twelve or fifteen quarts of wa ter xill wholly dissolved ; the vessel that contains this liquor is to be half filled with old iron made red hot, and the whole to be exposed to the air and light for a week ; an equal quantity of red-hot iron is to be thrown into as many quarts of vinegar, which is also to be exposed to the air and light : after some days, the two solutions are to he mixed together, and exposed to the air and light for ano ther week. The liquor is then to be decanted, and kept in a close vessel for use.
The linen or cotton left in this liquor for -tour hours acquires a good black. If the liquor does not contain iron enough, a fresh portion should be used, which will produce a permanent black. This liquor may be advantage ously substituted for sulphate of iron in dyeing wool or silk, which only require to be dipped in a decoction of logwood, after being taken out of the bath, to give them a beautiful black.
Berthollet mentions, that iron ought to be more oxygenated to unite with cotton or linen, than with wool or-silk ; and that therefore the longer the iron liquor is ex posed to the air the better. The place of galls, which hear an high price, is fre quently supplied by oak bark, oak saw dust, sumach, the cups and husks of acorns, and other astringents.