ASPECTS OF ADSORPTION PHENOMENA 189 



to be the case. Two solutions containing 0-005 per cent, of congo- 

 red were taken, one in 50 per cent, alcohol, the other in water. From 

 the former a circle of filter paper adsorbed at 14 in seventy 

 minutes 45 per cent, of its contents, and from the watery solution 

 only 30 per cent. 



The action of a neutral electrolyte, sodium chloride, was similar, 

 but more pronounced. From a solution containing 0*0042 per cent, 

 dye and 2 per cent. NaCi, 75 per cent, was taken up in fifty minutes, 

 and from a solution of the same concentration in dye, but without 

 NaCL, only some 25 per cent, was taken up at the same time. 



The action of strong acids is, of course, to set free the sulphonic 

 acid from its compound, the free acid while more soluble in alcohol is 

 less so in water, so that again we have a favouring effect on adsorp- 

 tion as follows : Two flasks of the usual 0^005 per cent, solution of 

 dye with each one circle of paper to 50 c.c. solution were prepared, 

 one remained neutral, the other was acidified by the addition of one 

 drop of 5 per cent. HCI. Though the solution became blue no pre- 

 cipitation of the colour-acid occurred in this weak concentration. 

 After two hours at 13 to 14, 35 per cent, was taken up from 

 the acid solution and 12 per cent, from the neutral one. Before 

 taking the colorimeter reading the acid solution was neutralized by a 

 drop of ammonia. 



It ap pears, then, that bodies which tend to diminish the solubility 

 of congo-red favour its adsorption by the substances immersed in its 

 solution. 



The experiment with gelatin and calcium sulphate, previously 

 rela ted, shows that the rate of adsorption in that case is considerably 

 greater than that of congo-red by paper, as would be expected from 

 the greater mobility of the ions concerned. At 11 equilibrium was 

 attained in less than two-and-a-half hours, whereas at the same tem- 

 perature at least twenty-four hours was required for congo-red and 

 paper. 



2. Equilibrium 



The most interesting fact under this head is the influence of 

 temperatnre. As the curve (Fig. 4) shows, at the higher temperature, 



