T. 



Oh thf U/e of Iron \n Dyhg, 



XII. 



Chemical Conjideratlons on the life of the Oxydes of Iron in the Dying ef CattiK^ 



By J. A. Chaptal *. 



H Eoxyde of iron has fo ftrong an attraSion to the fibre of cotton, that if the latter be- 

 plunged in a faturated folution of iron in any acid whatever, it affumes a chamois yellow 

 colour, of greater or lefs jntenfity, according to the ftr^ngth of the folution. It is no lefs- 

 curious than eafy to make the experiment of pafling a piece of cotton through a folution of 

 fulphate of iron rendered turbid by the oxyde which remains fufpended in the fluid. Nothing 

 more is neceffary than to pafs the cotton through the bath, from which it feizes the laft 

 particle of the oxyde, and reilores its tranfparancy. The folution, which before was yellowifh^ 

 immediately becomes more or lefs green, according to its ftrength. 



The colour which the oxyde of iron gives to cotton, 4)ecomes deeper by fimple expofure 

 to the air ; and this colour, which is foft and agreeable at firft taking out of the bath» becomes- 

 hard and ochreous by the progreflive oxydatioii of the metal. 



The colour of the oxyde of iron k very folid. It refifts the a£tion not only of the air and" 

 water, but likewife of alkaline folutions. Soap gives it brightnefs without perceptibly 

 diminifbing its intenfity. 



From thefe properties it is,' that the art of dying has availed itfelfof the oxyde of iron as a 

 moft valuable colouring principle. But I have fucceeded in giving a new extenfion to 

 the applicatic* of this oxyde. I (hall confine myfelf in prefenting to the Inftitute thofe refults 

 only which deferve to be adopted in the practice of manufadturers, and have been executed for 

 feveral years in my dying- works. 



In order that the oxyde of iron may be conveniently applied to the cotton .thread, its folutio» 

 tnuft firft be efFefted. Acids are ufed as the beft folvents. 



Moft dyers make a myftery of the acid they ufe ; but the univerlal praiElice is confined to 

 the acetous, the fulphuric, the nitric, and the muriatic acids. 



Some dyers attribute great differences to the acid they ufe in the folution of iron ; but the 

 preference is commonly given to the acetous acid. 



This prediledtion appears to me to be grounded much lefs upon the difference of the 

 colours, which one acid or the other may give, than upon the corrofive aftion which each of 

 them exerts to diff'erent degrees on the ftuff^. This is fo great, with refpefl to the fulphate 

 and the muriate, that if th^ piece be not waflied immediately as it comes out of the bath, itt 

 will certainly undergo an eff'eft of the fame nature as combuftion ; whereas the folutions in 

 the acetous, or any other vegetable acid, do not produce this inconvenience. , 



The iron appears to exift at the fame degree of oxydation f in the different acids, fince it 

 produces the fame fhade of colour when precipitated ; and any acid fait may be indifcrimi- 

 jiately ufed, provided the nature of the fait, and the degree of faturation in the acid, be fufficiently 



• Read to the French National Inftitute, 21 Germinal, in the fixth Republican year, and inferted in 



the Annales de Chimie, XXVI. 266, whence this tranflation is made. 



f On this fubjefl fee, however, the Philof. Journal, I. 453. 



known J 



