8 Dr. Thomas Thomson on [Jan. 



the affinity of the alumina for the cloth, that the acetate of 

 alumina, and even a portion of the alum, are decomposed, 

 and the particles of alumina adhere to the fibres of the cloth 

 so firmly that they cannot be removed by washing. 



In order to determine the quantity of alumina fixed on 

 on the cloth by the aluming process, I got a quantity of 

 the cotton cloth that was to be dyed Turkey-red ; 1000 

 grains of this cloth were burnt, and the ashes being re- 

 served, and subjected to a chemical analysis, were found to 

 contain 0*4 grain of alumina; 1000 grains of the same 

 cloth after being dyed Turkey-red, and of course, impreg- 

 nated with the alum mordant, were treated in the same 

 way. The alumina obtained amounted to 8 grains. The 

 length of a piece of this cloth, weighing 1000 grains, was 

 1 yard 5§ inches, and its breadth 33 inches. Thus, a piece 

 of cloth, amounting to 1386 square inches, or rather, 2772 

 square inches, (as both sides of the cloth had been equally 

 subjected to an aluming process) had combined with 7*6 

 grains of alumina ; or every square inch of the cloth had 

 combined with 0*0027 grains (^th of a grain nearly) of 

 alumina. 



1000 grains of the same cloth were dyed the palest 

 shade of Turkey-red usually given to cloth. When burnt, 

 the ashes were found to contain 0*8 grain of alumina. 

 Subtracting the 0*4 grain of alumina belonging to the 

 cotton fibres, there remains 0*4 grain for the quantity 

 communicated during the aluming process. In this case, 

 every square inch of surface of the cloth had combined with 

 0-00012 grain of alumina, or less than g^th of a grain. 

 Yet this quantity of alumina small as it is, was essential 

 to the permanence of the dye. For, when unalumed cloth 

 was dyed with madder, the colour was easily washed out 

 with water. 



When cloth to be dyed red is impregnated with this 

 mordant, it is not thickened. When applied only to par- 

 ticular parts of the cloth, by the block or cylinder, it is 

 thickened with flour, qr calcined starch, or gum Senegal, 

 according to the nature of the style of work. 



2. Oxide of tin. Perchloride of tin is very much used 

 as a mordant. The colouring matter is previously mixed 

 with it, and both are applied at once. Such applications 



