in dyeing Cotton red. 277 



Which is not very foluble in water, and which has the greateft 

 affinity with the colouring principle of the madder. The 

 dyer may acquire a competent knowledge of this laft com- 

 bination, and itudy its properties, by mixing a decoction of 

 gall nuts with a folution of foap. 



It follows from thefe principles : I. That the place of the 

 gall nuts cannot be fupplied by any other aftririgent, let the 

 quantity employed be what it may. 2. That the galls ought 

 to be (trained as hot as poflible, that the decompofition may 

 be fpeedy and perfect. 3. That the galled cotton ought to 

 be fpeedily dried, in order to prevent its affuming a black 

 colour, which would injure the brightnefs of the red intend- 

 ed to be given to it. 4. That dry weather ought to be 

 chofen for the procefs of galling, becaufe in moift weather 

 the aftringent principle communicates a black colour, and dries 

 flowly. 5. The cotton ought to be preffed together with the 

 greateft care, in order that the decompofition may be ef- 

 fected in an equal manner at every point of the furface. 

 6. That a proportion ought to be eftablifhed between the 

 gall nuts and the foap : if the former predominates, the co- 

 lour is black j if the latter, the portion of the oil not com- 

 bined with the aitringent principle then e.fcapes by the warn- 

 ings, and the colour remains poor. 



The third mordant employed in dyeing cotton fed is the 

 fulphate of alumine (alum). This fubftance not only has 

 of itfelf the property of heightening the red of madder, but it 

 contributes alfo by its decompofition and the fixation of its 

 alumine to give folidity to the colour. To judge of the ef- 

 fects of alum in dyeing cotton, it will be fufficient to mix a 

 decoction of gall nuts with a folution of alum. The mixture 

 becomes immediately turbid, and there is formed a greyifh pre- 

 cipitate, which, when dried, is infoluble in water and alkalies. 



Every thing that takes place in this experiment of the la- 

 boratory may be obferved in the procefs of aluming in dye- 

 ing. Cotton, when galled and plunged in a folution of the 

 falfate or acetite of alumine, immediately changes its colour, 



T 3 and 



