5^ On Bleach'ingi 



definite eflay of Higgins prefuppofes too much previous know- 

 ledge in the reader, ever to enable the inexperienced to adapt 

 or eftablifh the new procefs; and the many other detached 

 eflays *, however valuable on particular parts, are yet far 

 from forming a whole, whence the practical bleacher might 

 gain inftrutStion to adapt or improve this new fynem. The 

 prefent eflfay not only prefents a coinplete view of all -that has 

 hitherto been publifiied, but adds many original facls to the 

 illuftration of the modus operandi, or theory snd praftice of 

 bleaching. It is therefore with no inconfiderable deference 

 that I venture to offsir fome remarks on the work of fo expe- 

 rienced a chemift. 



That there Ihould ftill be fuch a diverfity in the quantity 

 of the ingredients for preparing the oxymuriatous acid may 

 appear (tringe, when its nature and properties are fo well 

 imderftood. This may be accounted for only by the peculiar 

 modes of preparing it, for the end of all is the fame. The 

 firft attempts to prepare this acid fit for bleaching often fail, 

 and the caule of fuch failures, owing, perhaps, only to the 

 want of manual dexterity, is generally afcribed to a deficiency 

 in the quantity of fome of the ingredients. To remedy this 

 jrippofed deficiency, an unneceffary quantity of fome one ar- 

 ticle is added : hence the German pradlice of ufing 64 parts 

 fait to 20 mangauele, when molt probably the converfe quan- 

 tities, properly managed, would have much fooner produced the 

 defired eft'eft. The ufe of fait in this procefs has, no doubt, 

 hitherto been greatly over-rated. It does not appear that 

 muriatic acid alone pofflffes anv bleaching powers, but that 

 ofdepofiting a pale iubltantive yellow upon cverv other colour. 

 To oxygen, of which it is only the vehicle, isjuilly afcribed 

 the deterfive property of oxymuriatous acid ; and ftuffs are 

 whitened with greater or lefs celerity, according to their 

 greater or lefs facility of combining with oxygen. The co- 

 louring matter undergoes a real flow combuliion, which ter- 

 minates bv the formation of carbonic acid, which, efcaping 

 under the form of elallic fluid, produces what we call bleach- 

 in^. Granting that comhuflion atlually takes place, (in 

 which there is no iefs of theory than experiment,) and the 

 rtxygen, uniting with the carbon, efcapes in the flate of car- 

 bonic gas, the muriatic radical and bafe of the colouring 

 matter nuifl unite and form a concrete fubftance ; the refi- 

 duary produft of combuftion, which literally dyes a leaden 

 white, and which, like leaden paint, on expofure to the at- 

 m6fphere, fliortly afiumes a dirty yellow colour. That this 

 is really the cafe can fcarcely be doubted ; and that all the 



■-'■ It is polFibk I'oine of tliefe may have efcapcd the writer's attention. 



attempts 



