ASPECTS OF ADSORPTION PHENOMENA 199 



There are some irregularities especially as regards NH* salts. The 

 value put against cso means that the concentration had to be taken 

 at .- - to avoid precipitation, and at this strength the value was 84 

 per cent. 



The action of ^~ H and ^ ions needs a little further explanation 

 since it seems to vary according to concentration in both cases. It is 

 somewhat remarkable that in concentrations of ^ NaOH and Naci have 

 almost exactly the same amount of favouring action ; in on the 

 contrary, while Naci has a distinct favouring action, viz., 58 per cent, 

 adsorbed from Nad as against 30 per cent, from water, NaOH has a very 

 slight inhibiting action, viz., 25 per cent, against 26 per cent, from water. 



In one experiment I took three solutions of equal content in OH 

 ions, viz. : 



'NaOH ... 31% 



IOOO 



7T NH * H /'** 79% 



_"L Na 3 CO, 8 9 % 



100 /0 . 



The amount adsorbed in presence of these is shown opposite 

 each one. 



I could not detect any influence of anilin-water on the process. 



Sulphuric acid ^^ has a favouring action, 33 per cent, against 21 

 per cent, from water, while in ~ it has the opposite effect as the table 

 shows. I am unable to suggest any explanation of these facts. 



In connection with the well-known mutual precipitation of 

 oppositely charged colloids* the behaviour of congo-red as a negative 

 colloid is of interest. Colloidal platinum prepared by Bredig's method 

 does not precipitate, but has a chemical action, turning the dye brown. 

 This platinum sol is negatively charged so that precipitation would not 

 be expected. On the other hand, according to Pauli 1 and other 

 investigators, the precipitating action of salts of the heavy metals on 

 egg-wh;te is due to the presence in their solutions of metallic 

 hydroxide in the colloidal form and presumably positively charged. 



1. S-e Picton and Linder, Journ. of C him. Soc., 1892, page 148, etc., and W. Biltz, \Ber d. Deuhcft. 

 Chtm. Ges., 1904, Bd. XXXVII, page mi. 



2. Hot'meister's Beitrizge, VI, page 257, 1905. 



