Cempaund Colours produced en Cotttn by the Oxyde of Irtn. IS9 



VII. 



Chemical Confiderattons on the Ufe of the Onydes of Inn in the dying ef Cotton. By J, Ai 



Chaj>7az. 



(Concluded from page 93.)' 



2. JL F the iron be precipitated from a folution rather ftrong by alkaline liquor, marking between 

 five and fix degrees of the areometer of Baume, the product' will be a bluifti green magma. 

 Cotton' macerated in this precipitate acquires at firft a dirty irregular green tinge ; but fimplc 

 expofure to the air converts it toa yellow, in a very Ihort time> of a very deep fhade. 



It is by a procefs nearly fimilar to this, that the ochre or ruft" colow of the fhops is formed; 



But thefe colours- are attended with various inconveniences, r. They either corrode the 

 the cloth or injure its durability. 2. This colour is harfhjdifagreeable, and cannot eafily be 

 combined with the foft colours- afforded by vegetables. 



I was defirous of remedying thefe inconveniences, and fucceeded by the following treatment; 



I work the cotton in' a cold folution, marking three degrees (fpecific gravity 1,02), then 

 carefully wring it with the pin, and afterwards^ phinge it in a f&lution of potafti at two degrees 

 (1,01 5), into which fulphate of alumine has been poured to &turation. By this means the colour 

 is brightened, and becomes infinitely finer, fofter, and more agreeable; — the fulphate does not 

 attack the body of the fluff; — and after having left the cotton in the (fecond) bath for four 

 or five hours, it is taken out to be preffed, wa(bed, and dried; 



By this procefs, every (hade which can be defired may be obtained by graduating the ftrength 

 of the folutions. The famples which I prefent to the inftitute are prepared according to this 

 method. This fimple procefs, of which the theory will prefent itfelf to the mind of every 

 chemift, poffefles the advantage of affording a very agreeable, very folid, and partidilarly cheap, 

 colour. I have ufed it with advantage for nankeens, of which the colour is infinitely more 

 fixed than that of the Englirti nankeens. It has the advantage over them in refifting alkalies, 

 and the only feult I know in it is that of acquiring a brown colour by the a£lion of aftringents. 



I was for fome time of opinion, that it might be poflibk to combine this yellow with the 

 blue of indigo, to obtain a folid colour. But hitherto my expectations have not been realized, 

 and the refults of the trials I have made are, that there is not a fufficient affinity between the 

 blue of indigo and the oxydes of iron. I obtamed only a dirty^ earthy, very deep, and unequd 

 green colour. 



The oxyde of iron, on the contrary, combines very eafily with the red of madder, aad 

 affords a light violet prune colour of very extenfive and advantageous ufe in cotton manu* 

 failorics. 



But if thefe two colours be applied to cotton without employing a mordant capable of fixing 

 the latter, the colour will not only remain dull and difagreeable, from the impoiHbility of 

 brightening it, but it will likewife have the very great inconvenience of not refifting alkalies. 

 It is proper, therefore, to begin the operation in the fame manner as when cottons are 

 prepared to receive the Adrianople red ; and when the goods are brought as far as to the 

 operation of galling, they are to be paffed into a folution of iron, more or lefs charged, accord- 

 Voi. III.— JuNB 1799, S ing 



