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which occasion the dark or dusky colour of flax, and the dunyellow colour of cotton. Bleaching was formerly, and still is,accomplished, by boiling the materials to be whitened, in alka-line leys, and steeping in weak acidulous solutions; which, to-gether with mill-washing, and exposure to the sun, constitutethe process of bleaching.
Bleaching by oxymuriatic acid .—Since the discovery of the oxy-muriatic acid, a new era has commenced in the art of bleaching,and the wonderful effects of this agent have been successfullyapplied to both cotton and linen. This liquid consists of muria-tic acid, or spirit of sea salt, as it was formerly termed, andoxygen gas; and the common mode of making it, is, by mix-ing certain proportions of sulphuric acid, manganese, and mu-riate of soda, and subjecting the whole to the process of distilla-tion. The sulphuric acid uniting with the alkali of the salt dis-charges the muriatic acid, which, combining with the oxygen ofthe manganese, rises in the state of vapour, and impregnatesthe water in the receiver, in which a quantity of potash had beenpreviously dissolved. To whiten the yarn or cloth, it is only ne-cessary to immerse it in this liquor. There are, however, cer-tain objections to this manner of using the oxymuriate, arisingfrom its offensive smell and injurious effects on the health of theworkmen. It was necessary, therefore, to obtain the acid in amore condensed state; and, accordingly, Mr Charles Tennentsuggested the method of combining the gaseous vapour withlime, thus producing the oxymuriate of lime, which, beingcheaper than that of potash, is now generally used in preferenceto any other mode of applying the oxymuriatic acid. For thisinvention he obtained a patent.
This compound being in a dry state, is easily carried from oneplace to another; and to produce a liquid fit for bleaching, it isonly necessary to mix a certain proportion of this bleaching saltwith a specified quantity of water: the yarn or cloth is then im-mersed in the liquid, and the acid immediately acts ; but, inmost cases, frequent immersions are required, particularly whenthe material is flax or hemp. The effect of oxymuriatic acid oncotton is so rapid, that it may be fully whitened in an hour. In-stances, indeed, have occurred where the cotton has been spun,woven and bleached, in the course of one day.
The discovery of bleaching by oxymuriates, has been attend-ed with important consequences to cotton and linen manufactur-es) as the expedition with which they finish their goods, saveswe long outlay of capital which the old method of bleaching
'equired.
This method of whitening cloth is not yet generally practised,being only partly used in conjunction with the common process;a "d it is doubtful if the oxymuriatic acid could be profitably ap-Phed to bleach linen without the assistance of boiling in alkalis,Ndl-washing, and exposure to the sun.