250 



solids as platinum spong-e 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 verv 

 superticial 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 ac-count of a possible ^chano-e iu 

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

 ims been done to learn how general this effect is among solids and amon^. 

 solutions, and very little to ascertain the magnitude of the chan<.e pro''- 

 duced. The results obtained by different observers are ditticult to harmon- 

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

 O^etween certain solids and certain solutions; a few attempt a (juantitative 

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

 conclusi,>ns; a very few investigate the intluenc-e of concentration-with 

 more or less contradictory results. One <-laims that the adsorbed .luantity 

 that is. the w(>ight of the solute close to the solid surface in excess of that 

 in the same volume of otlu-r parts of the solution, is not dependent on the 

 concentration iu the strict sense of Henry's Law, but that dilution always 

 lowers the .iuantity of the dissolved substance in the solution more 

 mark(>dly |],an that of tlu> adsorbed substance; another, that Henry's Law 



applies throughout approximately: still ; Uwv ascribes the results to 



chemical union and not physical attraction. 



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

 a series of expei-iments 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 phuv here, .-ind some factors now realized to 

 be essential to their interpretation were not recorded, but bi-iefly, tlie ex- 

 periments showed the following facts: 



Twentieth-normal tartaric acid showed a loss of nearly 12 per cent. I,y 

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

 same with filter paper; 2.0 per cent, sucrose solution with animal charcoal 

 was reduced to L9 per cent.: fiftieth-normal acetic acid with silica gave 

 ovei- 5 per cent, loss; fiftieth-normal hydrochloric acid with silica'^^.-j 

 per cent, loss; fiftieth-nm-mal 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, 



