250 



solids as platinum sponge may probably be attributed to this surface at- 

 traction. 



That solids in contact with solutions concentrate the dissolved sub- 

 stances on their surfaces, has been assumed in many cases, and some very 

 superficial quantitative experiments carried out. It is commonly accepted 

 by analysts that the first portion of the solution passing through a filter 

 should be rejected in volumetric work on account of a possible change in 

 concentration due to the action of the filter, but little experimental work 

 has been done to learn how general this effect is among solids and among 

 solutions, and very little to ascertain the magnitude of the change pro- 

 ((luced. The results obtained by different observers are difficult to harmon- 

 :ize; most of the experimenters simply show that adsorption takes place 

 between certain solids and certain solutions; a few attempt a quantitative 

 examination but omit to report factors essential to the drawing of general 

 conclusions; a very few investigate the infiuence of concentration— with 

 more or less contradictory results. One claims that the adsorbed quantitj'. 

 that is, the weight of the solute close to the solid surface in excess of that 

 in the same volume of other parts of the solution, is not dependent on the 

 ■concentration in the sti-ict sense of Henry's Law, but that dilution always 

 lowei's the quantity of tlie dissolved substance in the solution more 

 markedly than that of the adsorbed substance; another, that Henry's Law 

 applies throughout approximately; still another ascribes the results to 

 chemical union and not physical attr^action. 



About four years ago the writer, with Donald Davidson, carried out 

 a sei-ies of experiments to learn how general the adsorbing action of solids 

 on solutions might be, and the magnitude of the effect. The details of the 

 experiments would be out of place here, and some factors now realized to 

 be essential to their interpretation were not recorded, but briefly, the ex- 

 periments showed the following facts: 



Twentieth-normal tartaric acid showed a loss of nearly 12 per cent, by 

 -contact with filter paper; twentieth-normal potassium hydroxide about the 

 same with filter paper; 2.6 per cent, sucrose solution with animal charcoal 

 was reduced to 1.9 per cent.; fiftieth-normal acetic acid with silica gave 

 over 5 per cent, loss; fiftieth-normal hydrochloric acid with silica 2..5 

 per cent, loss; fiftieth-normal hydrochloric acid with cotton cloth 4 per 

 cent, loss; fiftieth-normal ammonia with cotton cloth about 15 per cent, 

 loss. All of these experiments showed, then, a positive adsorption of from 

 2.5 to 15 per cent, of the dissolved substance. Several others, however, 



