III. Soap is an article so well known, that it re quires no particular description. It is sold of three different kills, viz. brown, white, and soft soaps. It is the two latter kinds which are chiefly used in bleaching ; the former being commonly sold for house hold washing in some parts of Britain.
IV. Of all the agents used in bleaching, there is none of them which ranks higher for giving facility and dispatch to the various operations than the oxy -muriatic acid.
We might even at this moment have been unac quainted with the cause of the destruction of the co louring matter of vegetable substances, if the disco very of this acid, and its effects on colouring matter, had nut pointed it out to us. For this discovery, and its inestimable advantages, the arts are indebt ed to the celebrated Scheele. While employed in making experiments on manganese, about the year 1774•, he noticed its powers in rendering vegetable substances colourless, mbre as a matter of curiosity than of use. Having communicated his observa tions to Berthollet, in France, about the year 1786, the latter lost no time in applying the properties of this curious and interesting substance to the most im portant practical purposes. His application of it to the bleaching of cotton and linen cloth proving suc cessful, he published the result of his experiments in the year 1789. The new method of bleaching was quickly and successfully introdUced into the manu factories of Rouen, Valenciennes, and Courtray ; and soon after into those of Manchester and Glasgow ; and it has since been generally adopted in Great Bri tain, Ireland, France, and Germany. The advanta ges which result from this method of bleaching, in every season of the year, can be best appreciated by commercial people who experience its beneficial ef fects in many ways, but particularly in the quick circulation of their capitals.
Great difficulties at first impeded its progress, ari sing chiefly from prejudice, as well as from the igno rance of the bleachers in chemical processes. These obstacles were however soon removed by the assist ance of several eminent chemists at Glasgow and Manchester, particularly Messrs Watt, Henry, and Cooper. Sec p. 577, Note..
Mr Berthollet's process for forming the oxymu riatic acid, consisted in distilling one part of the black oxide of manganese with two parts of muria, tic acid, in a glass retort : the product of the distilla tion was received in glass bottles, properly applied, when the quantity was small, or into a receiver lined with lead when the quantity was larger.
From the volatility of the oxygen as united with -c muriatic acid, when simply diffused in water, with which it has a very slight affinity; and, conse quently, its unequal action on the goods which were immersed in it for the pm-pose of being whitened, and its discharging those colours which were wove into the goods intended to remain permanent ; as well as the suffocating- vapours arising from it pro ving hurtful to the health of the workmen employed, it soon became evident, that the appl:cation of it in an extensive manner would be impracticable if these difficulties were not more or less removed. Various attempts were made to effect this ; and since it has been accomplished, a number of persons have put in their claims as the inventors of so advantafeous an improvement. Mr Higgins of Dublin and Mr Ber thollet had both combined the oxymuriatic acid with potash, so early as the year 178S. The km wledge of the latter's having done so, and that the acid was thereby deprived of its offensive smell, induced the bleachers at Javelle, in France, to add a solntion of caustic potash. Hence the oxvmuriatic acid com bined with an alkali, is usually known by the name of the Javelle liquor.
Notwithstanding this evident improvement, it was still generally maintained by chemists, that the oxy muriatic acid, united simply with water, possessed greater bleaching power than that which is combined with caustic alkali ; but this was contradicted by the practical bleachers, whose experience taught them, that though the acid, thus combined with an alkali, whitened with somewhat less rapidity, it had the ad vantage of retaining the gas much longer in open ves sels, and of preserving fixed dyed colours, such as the Turkey or Adrianople-red. These facts arc now so fully established, that although several attempts have been made. since the year 1796, again to introduce the oxymuriatic acid, diffused simply in water, into air tight vessels, to prevent its offensive smell, yet, from a conviction of its absurdity, it has been adopt ed only by a few.