In the year 1815, in consequence of the joint ap plication of the bleachers, the duty on common salt, formerly charged upon all bleachers and others who employed that article in the preparation of a bleach ing liquid, was taken off, and they were henceforth allowed to use it duty free. But this act, while it affords great advantages to bleachers on a large scale, precludes those who only work on a small scale, making their own oxymuriate of lime; the consumption of the powder, therefore, is likely to increase very much among the little bleachers and calico printers. Its use is also considerable in partially discharging the colour of Turkey red cloth. The method was originally a French invention ; but a patent has been lately granted to Mr Thomson, a Lancashire bleacher, for the process, which, we be lieve, he imported from Ion y. The method is this : An acid paste, consisting of citric acid, or any other acid thickened with gum, is first printed on the Tur key red cloth, which is then passed through liquid oxymuriate of lime. It becomes white only where the acid was On this bleached put sal other colour may be applied, and the combinations 'produced are exceedingly beautiful and striking. • Such, as far as we are acquainted with the sub ject, is the history of the progress of the new me thod of bleaching in Great Britain. We have said no thing of the Irish bleachers, because we are not par ticularly acquainted with the progress of the new me thod in that country ; though we believe that oxymt. riatic acid was tried by the Irish bleachers almost as early as it was in Great Britain. Mr Parkes supposes that Mr Kirwan might have proposed the trial of the new reagent, in consequence of some suggestion from Scheele or Saussure. (Parkes's Chemical Essays, IV. 43.) But we have no evidence that this was the case. Indeed, it would be quite unreasonable to attempt, by such vague suspicions, to detract from the merit due to Berthollet for his original suggestion of the appli cation of oxymuriatic acid to bleaching,—a merit which he has enjoyed without a competitor for SO years. Scheele was dead before any one attempted to introduce the new acid into bleaching, either iii Great Britain or Ireland. And there is every rea son for believing that Saussure's knowledge of the bleaching qualities of oxymuriatic acid, originated from Berthollet's publications on the subject in 1785 and 1786.
There are three different ways of employing oxy miriade acid in bleaching,' still followed by different manufacturers ; the first, the simplest, and we may add, the most economical and efficacious mode, is to impregnate water with oxymuriatic acid, and to use this liquid without any addition in a sufficiently di luted state. Mr Rupp, long ago, demonstrated the superior economy of this process, and even at pre sent it is used by the great house of Oberkampf, Widmer, and Company, of lony, near Versailles, who have contrived a very ingenious apparatus for its preparation. The only objection to this mode of using the gas, is its suffocating odour, which ren ders it injurious to the health of the workmen em , ployed.
But the method universally employed by the great bleachers of Britain and Ireland, it to form a liquid oxymuriate of lime, and to immerse the goods in it. The gas is always obtained from com mon salt, by the joint action of sulphuric acid and black oxide of manganese. Various propor
tions of these ingredients have been recommended by different persons ; but none of them seem to have founded their numbers on scientific considerations. Berthollet, in his dissertation on this subject, pub lished in 1789 (dnnales de Chimie, II. 165), commends the following proportions as the best These numbers are founded on the supposition, that two atoms of sulphuric arid are requisite to disengage one atom of muriatic acid from common salt, which, at the common temperature of the atmosphere, or when the heat of boiling water is only applied, is probably true ; though at higher temperatures we know, that one atom of sulphuric acid will iirive off one atom of muriatic acid. If we consider the state of the common salt, as it is employed, and the fre quent impurity of the oxide of manganese used, pro bably the bleachers would find the following pro ' portions the most economical and advantageous At present there can be no doubt that the propor. tion of common salt used by the bleachers is too great. It is well known, that what remains in the stills after the process, contains still a considerable proportion of muriatic acid. Thus Mr Wilson found the salt which crystallized in the liquid resi duum, after distillation, was composed of by no means applies to the processes of the Bleaching.
flgaso er.
The third state in which the oxymuriatic add is employed by bleachers, is combined with lime, con stituting dry oxymuriate of lime. Hitherto the ma• nufacture of this salt in Great Britain has been con fined to Mr Tennant of Glasgow, the inventor of the process. But his patent being now at an end, other persons have begun to make it in the neigh bourhood of Manchester. For the manufacture of this salt, leaden stills are employed, similar to those used in making liquid oxymuriate of lime, and like wise cast-iron stills. The gas is conveyed into a close wooden vessel, on the bottom of which is spread some quicklime, newly slaked and sifted. As the gas passes over, it combines with the lime, and gradually forms the salt required. It is a soft white powder, possessing little smell. When heat ed it gives out oxygen gas ; but if it be mixed with sulphuric acid, oxymuriatic gas is given out when the heat of a lamp is applied. It is partially solu ble in water, and the solution gradually disengages bubbles of oxygen gas, while the salt is changed into common muriate of lime. This change appears to take place gradually, even when the salt is kept in a dry state. Mr Dalton has analyzed this salt, and found it composed of Dr Henry of Manchester found very large pro portions of common salt and muriate of manganese in the residue left after distillation ; and he inform ed the writer of this article, that he had known a bleacher, when in want of common salt, to work twice from the same ingredients, by adding fresh manganese and oil of vitrol. This is a sufficient proof that vastly too much common salt is employed. In. deed, the consumption of common salt by the bleach ers is enormous. One bleacher in Lancashire, for ex ample, uses, every six weeks, four waggon loads of common salt, each load containing 3 tons 13 cwt. This is almost at the rate of two tons and a half of salt per week. He employs, for his process, 22 leaden stills, each 22 inches deep, and about 2 feet 4 inches in diameter. Eleven of these are worked on alternate days.