T H E MORDANTING OF WOOL WITH POTASH ALUM BY W. W. PADDON
Although potash alum is one of the most common mordants used in the dyeing industry, little is known regarding its real action and the composition of the mordant on the fibre. Knechtl states that, “it appears that not only the hydroxides but true basic aluminum salts are deposited by the mordanting process in the fibre.” The only evidence given in support of this view is the fact that on dyeing well-washed wool with alizarin, the spent liquors invariably show an acid reaction. It is, however, unnecessary to postulate the presence of sulphuric acid in chemical combination, for adsorbed sulphuric acid should be displaced by the alizarin with equal readiness. Furstenhagen and Appleyard,2 give data to show that the amount of sulphate in the fibre remains constant when mordanted from solutions of potash alum containing 10 to 20y0 of the alum on the weight of the wool. No information is given t o show whether the sulphuric acid is adsorbed by or cornbined chemically with the alumina. .Havreza and von Georgievics4 are of the opinion that from baths containing above 24% of potash alum on the weight of the wool, alumina and sulphuric acid are adsorbed in the same relative amounts as they occur in A12(SrO)s. Up to 24% the amount of sulphuric acid taken up by the wool increases relatively to the wool as the concentration rises. ’ None of these investigators have determined the amounts of both alumina and sulphuric acid removed by wool from potash alum baths of different concentrations. Data of this nature have been found in the following way. Knecht, Rawson, and Lowenthal: “A Manual of Dyeing,” p. 237 (1910). Furstenhagen and Appleyard: Jour. SOC.Dyers and Colourists, 1888,105. 3 Chem. Centralblatt, 1’874, 696. 4 Jour. SOC.Chem. Ind., 14, 653 (1895). 1
2
The Mordanting of Wool with Potash Alum
791
Two-gram samples of well-washed wool were boiled for 1 hour in baths of potash alum of varying concentrations After the one hour, the wool was removed when hot and an aliquot portion of the bath analyzed in the usual gravimetric manner for aluminum and for sulphates. The results have been expressed both in grams and in percentages referred to the alum andzto the wool, the aluminum as A1203 and the sulphurjc acid 91) GRAMS Alp03 AT O
1
N
0
4
+
0
9
[ P
4&& S RBE%PER
GRAMS
wo
02
a L
as SO3. I n the baths of higher concentrations, it was noticed that, upon boiling, a precipitate formed on the bottom of the flasks. This precipitate was found to contain aluminum, with only slight traces of sulphates. The amount of this aluminum was determined and added to the amount already found in each case to have been left in the bath. The values obtained are tabulated below.
W . W . Paddon
782
TABLE I 7"Potash alum on weight of wool
0.0112 0.0225 0.0337 0.0450 0.0562 0.0676
5,12 10.25 15.37 20.50 25.62 30.75 % Potash alum on weight of wool
5.12 10.25 15.37 20.50 25.62 30.75
Yo Potash
alum on weight of wool
On'g. conc. Ah03 End conc. A1203 Grams A12O3adsorbed grams/250 cc grams/250 cc per 2 g wool
I
,
Orig. conc.
0.0035 0.0101 0.0215 0.0348 0.0476 0.0614
0.0077 0.0124 0.0122 0 * 0102 0.0086 0.0062
End conc.
g Sod250 cc
g SOa/250 cc
0.0346 0.0692 0.1037 0.1383 0.1730 0.2075
0.0224 0.0511 0.0815 0.1141 0.1461 0.1811
A1203
referred t o alum
Conc. in %
% in soln.
5.12 10.25 15.37 20.50 25.62 30.75
3.3 4.8 6.8 8.3 9.1 9.8
I
Grams SO3 adsorbed per 2 g wool
0.0122 0.0181 0.0222 0.0242 0.0269 0.0264
A1208
referred t o wool
% in wool
% in soln.
7.4 5.9 3.9 2.4 1.6 0.9
0.17 0.49 1.07 1.74 2.38 3.07
'
I
% in wool
0.38 0.60 0.60 0.49 0.42 0.30
wool
Conc. in %
% in s o h
% in wool
% in s o h .
% in wool
5.12 10.25 15.37 20.50 25.62 30.75
21.8 24.9 26.5 27.8 28.5 29.5
11.9 8.8 7.2 5.9 5.2 4.2
1.1 2.5 4.1 5.7 7.3 9.1
0.6 0.9 1.1 1.2 1.3 1.3
The Mordanting of Wool with Potash Alum
,
793
The data have been plotted in the form of the curves shown. In the case of the SOS, a smooth curve is obtained, indicating the adsorption of SO3 by the wool and the absence of sulphate compounds in the mordanted wool. In the case of alumina, the curve is likewise free from sudden breaks that would indicate the formation of chemical compounds. It passes through a peculiar maximum. This is probably due to the fact that considerable alumina was precipitated on boiling, presumably as A1(OH)3, and the concentration of the alumina in the bath, as far as the wool was concerned, was considerably altered thereby. As far as the data obtained in these experiments are concerned there is no basis for Knecht's belief in the presence of basic aluminum compounds on the fibre. The formation of such compounds would evidence itself as sudden breaks in the adsorption isotherm. No such breaks were found. Furstenhagen and Appleyard, in obtaining their results, apparently took into account only the SO3 present in Alz(S04)3of the potash alum and neglected both in their analytical work and their calculations the SO3 present in the K2S04of the alum. Above conc. of 20% of alum on the weight of the wool, the amount of SOa adsorbed is quite constant, but this does not indicate the formation of a basic sulphate for at the same concentrations the amount of alumina adsorbed steadily decreases, and morover the SO3 adsorption isotherm shows no sudden break. It can therefore be concluded that the mordanting of wool with potash alum does not lead to the formation' of definite chemical compounds on the fibre, but that it is strictly an adsorption phenomena, involving both alumina and sulphuric acid. This work- was carried out under the direction of Professor Bancroft, and was made possible by a grant from the Chemical Foundation. Cornell University
