The temperature of steam, under the pressure of the atmosphere, is sufficient to expel the whole of the oxymuriatic acid, and nothing is gained by em ploying a stronger heat. Accordingly, the stills are universally heated by steam. The calculation is, that 25 square feet of surface in the boiler, is suffi cient to heat six stills of the dimensions given above, into each of which are put 112 lbs. of common salt. The gas is received into cream of lime, in which the lime is kept suspended by mechanical agitation. When the process is finished, the undissolved lime is allowed to subside, and the clear liquid is drawn off. Its specific gravity is, generally, about 1.0125. Liquid of this strength is usually mixed with five or six tithes its bulk of water, before the goods are immersed in it. It has been said, that muriate of lime always injures the texture of cloth immersed in it. But this is true only when the solution is concentrated, and when it is used boiling hot ; but When the salt is dissolved in water, one-half of the lime is precipitated, so that the compound whidh was formerly a subchloride of lime, is now convert ed into a chloride. Its' constituents are, When a current of oxymuriatic gas is passed to sa turation through water in which lime is suspended, a bichloride of lime is formed. It is composed of From Mr Dalton's experiments, the oxymuriate of lime of commerce contains one-third of its weight of common muriate of lime ; but this portion varies according to the age of the salt, always increasing, . till at last the whole is converted into common muriate of lime.
II. In the article BLEACHING in the Encyclvadia, very copious extracts have been given from Kirwan, Berthollet, Decharmes, 0,reilly, Rupp, &c. with de scriptions and drawings of the different. apparatus recommended by them. But the reader of that ar• title will be at a loss to form any idea of the method of bleaching at present employed by the most en ' lightened bleachers in Great Britain On that ac count, we conceive that it will be requisite to give a concise sketch of the different processes as they oc cur in a practical bleachfield. We shall omit most of the descriptions of apparatus, which would oblige us to repeat many things contained in the article to which this is a supplement. The bleaching apRa ratus is sufficiently simple to be easily conceived by the reader without many particular descriptions. Cotton being much more easily bleached than linen, it will be requisite (though the processes are nearly the same) to give the method of bleaching each se parately, because the quantity of materials employed differ for each.
Bleaching of Linen.
It would appear from the new process of Mr Lee, who separates_the woody matter from the fibre of flax without steeping it, by means of mechanical ac tion, and then bleaches his flax by simply washing it in warm water, that the colouring matter is not che mically combined with the fibrous matter, while the plant is vegetating, or after it is pulled, but that the chemical combination takes place while the plant is steeped in water. The object of this steeping is to
induce a fermentation which loosens and destroys a cement which bound ;he fibres of flax to each other and to the wood. This fermentation weakens con siderably the strength of the flax fibres," and even destroys many of them.. Mr Lee's process, there fore, if it be practicable on a large scale, would be a prodigious improvement. It would render the flax fibres much stronger, it would increase their quan tity, and it would save the expence of the materials employed in bleaching the linen. The writer of this article has been informed that Mr Lee's process has uniformly failed of success, when tried in Ireland. If this account be true, it is extremely difficult to explain it. We have seen Mr Lee's process per formed by workmen under his own direction at Old Bow, near London, with the most complete success ; not merely upon handfuls of flax, but upon whole fields of it. Indeed, the whole is so extremely simple, that we cannot well see how it should fail, if proper ly conducted. We cannot, therefore, help suspect.. ing that the prejudices of the Irish, with which it would have to contend, have been too powerful for it ; but that, as soon as it shall meet with fair play, it will be found just as practicable, and certainly much cheaper and better, than the methods at pre sent in use.
It is during the steep, then, that flax acquires its permanent dark colour ; and four processes, which we shall now briefly describe, are requisite to re store it its original white colour, or to separate the colouring matter, which is chemically combined with the fibres of the flax.
1. When the flax is converted into thread, it is repeatedly moistened with the saliva of the spinner, which leaves attached to it a quantity of albumen. When the thread is woven into linen, it is covered with the weaver's dressing, which consists of a paste, made of flour and water. The first step of the bleacher's process is to remove these foreign bodies that the colouring matter of .the flax itself may be Blew* laid open to his subsequent operations. For this purpose, the goods are immersed in warm water, or in a warm alkaline ley; which has already been used in the bleaching processes to be described imme diately. In this situation they are allowed to remain till some degree of fermentation appears on the sur face of the liquid with which they are covered. This appearance takes place sooner or later, accord ing to the nature of the goods and the heat of the weather, and it is allowed to continue longer or shorter according to circumstances. The goods are then taken out, and well washed in pure water, which now removes all the foreign matter added during the spinning and weaving.