276' On the Effect of Mordants 



foda that has been long prepared, or is impure, cannot b$ 

 applied to the purpofes of dyeing in this manner. 



The choice of the oil is equally efTential as that of the foda. 

 The oil, to be good, muft unite very perfectly with the ley 

 of foda, and muft remain in an abfolute and permanent ftate 

 of combination. The oil fitteft for this dye is not fine oil, 

 but that rather which contains a large portion of the extrac- 

 tive principle. The former does not preferve its ftate of 

 combination with the foda, and requires fuch a ftrength in 

 the ley as would be injurious to the fubfequent operations. 

 The latter forms a thicker and more durable combination, 

 and requires only a weak ley of one or two degrees. 



The neceffity of producing a perfect and intimate combi- 

 nation of the oil and the foda will be readily perceived, by 

 reflecting that the ley of foda is only employed to divide, 

 dilute, and convey the oil in an equal manner to all the 

 parts of the cotton : for it follows from this principle, that 

 if the oil is not well mixed, the cotton made to pafs through, 

 this mordant will take the oil unequally, and the colour, 

 therefore, will be badly united. Hence it happens that 

 the workman places the whole fecret of a well-united and, 

 ftrong colour in the choice of good oil and fuitable foda. 

 It thence follows from thefe principles that the oil ought 

 to be in excefs, and not in a ftate of abfolute faturation ; for 

 in the latter cafe it would abandon the fluff in wafhing, and 

 the colour would remain dry. 



When the cotton has been properly impregnated with 

 oil, it is fubjecled to the operation of being galled. The 

 ufing of the gall nuts is attended with feveral advantages : 

 I. The acid which they contain decompofes the faponaceous 

 liquor with which the cotton is impregnated, and fixes the 

 oil on the fluff. 2. The character of animalifation which 

 the galls have, predifpofes the cotton to receive the colour- 

 ing matter. 3. The aftringent principle unites with the oil, 

 and forms with it a compound which blackens as it dries ; 



which 



