tention of teaching bleachers to ascertain the quantity of carbonic acid fixed in ashes, and in lime-stone, and consequently of ascertaining the proportional quantity of lime, from different kinds of stone, which should be mixed with any quantity of the different kinds of ashes, and which would require all the gas contained in them, to restore the lime to a mild insoluble state. He ascertained the quantity of the gas in each kind of stone, and in each kind of alkali he had an opportunity of trying.* Dr. Black, with the like good intentions, published an explanation of the effects of lime upon alkaline salt, and pointed out a method whereby it may be used with safety and advantage in bleaching. His method and conclusions are, one half of kelp that is commonly used will be sufficient, when sharpened with lime; twenty pounds of dry slaked lime may be mixed with every hundred of kelp; the same is said of cashup or markoff ashes. Spanish kelp, or barilha ashes will bear one half of its weight of lime, and then one fourth of this kelp that is employed at present, will answer the purpose. Pearl-ashes will probably require double or treble their weight of lime, and will become so much the more active and powerful, that they may be diminished to one fifth or one sixth of their usual quantity. Dr. M'Bride, formerly of Ballymoney, late of Dublin, wrote, for the benefit of bleachers, an abstract of these two Essays last mentioned.†

So small a quantity of quick-lime is soluble in water, as a sixhundredth or seven-hundredth part of the water. Leys used in bleaching cannot dissolve even so much. No danger therefore can arise, from using much more lime than the quantity prescribed.

SOAP.

Two or three kinds of soap only, are used in Ulster. First, hard white soap made of kelp or barilha and tallow. Second, hard

*If then leys free from fixed air, be most effectual in bleaching, does not the advantage appear of mixing so much lime with our ashes as is sufficient to attract the whole of their fixed air, and thus to bring them to their highest degree of perfection.

†These, with Dr. Home's Experiments on Bleaching, were published in Dublin, in 1771.

yellow soap, composed of soda, tallow and rosin; the rosin is added to render it cheaper; it is not used by our bleachers; the third is soft soap, made of pot-ash and fish-oil. It was long supposed that hard soap could not be made with pot-ash; we now make hard soap with it, by throwing common salt into the boiler.

Chaptal laid open to the world his discovery of a process of making soap from old woolen rags, and the refuse of woolen manufactures. Sir John Dalrymple, by a similar method, made soap from the muscular and cartilaginous parts of fat fish.*

SOURS.

The first sours used were butter-milk and infusions of wheaten or rye-meal; these are subject to three different stages of fermentation, the vinous, the acetous, and putrid. The acid continues to increase till the third commences, and with a rapidity proportioned to the temperature of the air. The period at which the putrid fermentation, which is hurtful to the fibrous texture, commences, is uncertain; wherefore, the mineral acids which are not subject to such changes, and which retard and oppose putrefaction, are universally used in Ireland.

When alkali attracts the carbonic acid from fire or from the atmosphere, it is not perfectly neutralized by it, but if this gas is thrown into caustic'leys, it is attracted by part of the alkali with so much avidity, as to become perfectly saturated with it; this part is then insoluble in water, as leys have an opportunity of uniting with the carbonic acid, when cloth is boiled in it; this salt is precipitated on the fibrous texture, and prevents the farther action of the alkali upon the colouring matter. This obstruction is removed by some other acid which has a stronger attraction for the alkali than the carbonic, and which, when united with it, forms a compound salt, soluble in water; this is the object desired in sours. Dr. Ferguson, when speaking of this salt, uses the language of Dr. Home, then common among chymists, and calls it an earth, because it was insoluble in water; he clearly de

* Both the above processes are given at large in the Phil. Mag. and Repertory of Arts of London. EDITOR.

scribed its qualities, and the method of obtaining and dissolving it.*

Any of the mineral acids dissolve this salt, but that which is very antiseptic, at the same time effectual and cheap, is the acid of vitriol; so called, because it was obtained from green vitriol, commonly called copperas, by distillation in earthen retorts made of fire clay; the residuum is colcothar.

It was long obtained for medical purposes, by burning sulphur, under a bell-shaped glass; the coldness of the air condensed the' vapour, which trickled down the glass, into a broad glass dish, placed below it. In a large work erected near Lisbon, in 1764, it was obtained by burning sulphur and a small quantity of nitre in large glass globes. These were expensive, and on a small scale; they gave place to great leaden chambers, in which the fumes of the burning sulphur are confined and condensed.

A quart of dephlegmated sulphuric acid, should weigh three pounds and three quarters; it is very seldom more than three pounds and a half. Ten naggins of such acid, are sufficient to make two hundred gallons of sour, of a proper strength for eighty pieces of yard-wide linen. I am assured that a quart of the sulphuric acid manufactured in Ulster, generally weighs more than three pounds eleven ounces, which the bleacher will consider when he measures the acid.

1

If the sour taste has been destroyed when the cloth has been six hours in the steep, too much of the acid has not been used. If the sour has been long delayed, a moderate quantity of it is insufficient to saturate the insoluble compound; but when sours are often repeated, and the same quantity of acid used, the part of the acid which is not saturated will act upon the fibrous texture and make it tender; each succeeding sour should be weaker.

The first sour should be tried with a hydrometer; if it loses its acidity by the salt attracted from the cloth, too much acid has

* It was proved in the thirteenth experiment, that some earth was precipitated from a ley, by its absorption of fixed air. As part, therefore, of the alkali becomes insoluble, it in part precludes the action of succeeding leys; it is necessary to take this earth out of the cloth, and this can only be done by the use of acids. Experimental Essay.

not been used; sour a little stronger, which raising the hydrometer a little higher, may be fixed upon as a standard for other sours, after an equal number of boils in ley of the same strength. When sours are long deferred, the alkaline compound precipitated upon the cloth, precludes, in a great measure, the action of succeeding leys; sours should be early applied, and they should not be again used till after some intervening boilings, and as heat increases the active power of solvents, the operation of sours applied warm, would be more expeditious and effectual. When linen is drawn out of the sour, it is washed, scalded in soap ley, soaped, rubbed, boiled, washed, and exposed on the grass. These manipulations are repeated, in Ulster, till a due degree of whiteness is acquired.

SMALTS.

In the last scald a small quantity of indigo is sometimes added; but indigo reflects a tinge too dark. The well known blue of laundresses is preferred and generally used. This is made from a metallic ore, or oxide, called cobalt, found plentifully in Saxony; when this ore is roasted, it is called zaffer; when this is fused with three parts of sand, and one of pot-ash, the product is blue glass; which, when pounded, sifted, and ground in mills, form smalts. That the blue may be obtained of various degrees of fineness, the smalts are agitated in casks filled with water, and pierced with openings at different heights. The azure brought by the water of the three different cocks, forms the different degrees of fineness, known by the names of azure of the first, second, and third fire; the second cock sends out azure of a very good quality for mixing with starch.

Saxony and Bohemia were long exclusively possessed of smaltworks. By the exertions of Compte de Beust, the French had divided the trade with Saxony; the Compte has found near the village of Juget, a quartz sufficiently charged with cobalt, which when fused for smalts, requires no additional quantity of the ore. Smalts are sometimes adulterated with hair-powder, which is easily detected by mixing them with water, the starch continues mixed with the water, the azure falls to the bottom.

When linen was starched, it was dried on the grass, or on hedges; but Mr. J. Nicholson, of Lawrence-town, on the Upper Bann, in the year 1727, demonstrated, that it was more conveniently and more perfectly done, in houses and lofts constructed for the purpose.

THE METHOD OF MANUFACTURING BLEACHING MATERIALS, IN ULSTER.-BY DR. S. M. STEPHENSON, OF BELFAST.

From the Belfast Literary Society.

WHEN this great mechanical apparatus, (erections and engines for bleaching) is constructed at eligible falls of water, and placed in suitable houses, in one of which two boilers, with convenient racks and keives are set, the bleaching stuffs or materials are to be provided. The principal are fossil and vegetable alkali, lime, sulphur, soap, acids, pure air and manganese.

The fossil or mineral alkali, when purified and crystallized, is now called sal soda; it is called natron when found native, as in Egypt, Syria, and India, countries famous for the early manufacture of fine linen; this, or water impregnated with it, was probably, after pure water, the first bleaching material. Sal soda is procured in this country, [Ireland] from almost every kind of sea-weed, as fucus serratus, vesiculosus and nodosus. The last, the knotted fucus, which has long slender stalks, leaves small bulbs or vesicles in the middle of the stalk, vulgarly called eelwrack, is most esteemed by our kelp-makers. In the months, of June and July, these, and other sea-weeds, growing upon the stones and rocks of our shores, are cut with hooks; if the weather is very dry and warm, the wrack is laid upon the dry shore, in small heaps, and allowed to continue in them without stirring, till it is fit for burning; if the weather is cold and damp it is spread out to dry, and then gathered into heaps, in which it is allowed to lie till it grows regularly damp; it is then burned in kilns; these are built upon dry hard ground, with square stones, without cement; they are generally fourteen feet long, three feet