9$ An Ejfay on Bleaching. 



fources for thofc peftilential exhalations with which the dc- 

 compofition of animal matters, by pntrid fermentation, is 

 always accompanied. 



The affinity of aggregation of thcfe fubftanccs, or that law 

 of adhefion wlfich keeps their molecular together, is weaker 

 than in the vegetable kingdom ; for this reafon they are fo 

 ealily dillblvcd and deftroyed by acids and alkalies, and hence 

 the rcadinefs with which aeriform fluids are produced. 



The bleaching of animal fubftanees requires the concur- 

 rence of alkalies, foap, ammonia, and fulphurotfs acid. We 

 Jhall here confine ourielves to an examination of wool and 

 filk, as the animal fublhinces molt generally employed, and 

 which it is of importance that manufacturers mould be ac- 

 quainted with the method of bleaching in the mod cecono- 

 mical and moft expeditious maimer. 



Of IVooL 



Wool is a kind of hair with which the bodies of fevera! 

 .animals are covered. It is compofed of filaments or tubes 

 filled with an oily or medullary fubftance. The fides of thefe 

 tubes are perforated with a multitude of fmall pores, which 

 communicate with the longitudinal tube. By chemical ana- 

 lyfis wool gives a great deal of oil and carbonate of ammonia: 

 cauftic alkaline leys defiroy it entirely; and it is to the facility 

 with which it difiblves in alkalies that, we are indebted for the 

 noble difeovery, made by C. Chaptal, of the foap of wool. 

 Wool experiences no change in boiling water : this observa- 

 tion is of great importance, in regard to the art of which we 

 are now treating; it alters very little when prefcrved in a 

 place well aired; acids have very little action on it ; when 

 expofed to a ih'ong heat it enters into fufion. All thefe fat% 

 united prove that wool is a femi- oleaginous fubftance. The 

 greafe with which it is covered when'on the body of the ani- 

 mal,, and from which it is freed by fcouring, ferves to con- 

 firm this aflertjon. 



* An examination of thefe chemical facts is necefTary for 

 underflanding the principles which ought to direct the artifl 

 in the bleaching of this fubftance. The little action which 

 acids have upon wool, and its unalterability in water, even 

 when aided by caloric, render it necefTary to have recourfe 

 to alkaline or faponaceous leys; but its folubility in thcfe 

 falts (hows that great prudence and caution mull be em- 

 ployed. „ In regard to acids, none have been hitherto ufed 

 but the fulphurous acid obtained in the gafeous ftate by com- 

 buftion. 



Of 



