14 BOTANICAL GAZETTE [JANUARY 
In the case of the starch grains, the potato tubers were crushed 
in a mortar, care being taken not to grind the material and crush 
the grains. The starch that settled out on washing was repeatedly 
washed with distilled water. Distilled water in which the starch 
grains were allowed to stand gave no trace of the starch reaction 
with iodine, a reaction which appears in case any considerable num- 
ber of grains are crushed, exposing the more soluble interior layers. 
Some hesitation, however, may be felt as to the insolubility of the 
grains. 
The question suggests itself as to whether all insoluble solids 
exert a like adsorptive action under these conditions (6). No attempt — 
was here made to test this question, since it was not practicable 
under the conditions of experiment given to work with the accuracy 
necessary in such a study. Furthermore, since adsorption is depend- 
ent to a considerable degree on the amount of surface offered by 
the solid, some way of taking account of this factor would seem 
necessary. In the case of sand this could be done, but to carry over 
these values to filter paper and starch grains, consisting of masses 
of organic substance supposed by some (7) to have a submicro- 
scopically porous structure, seemed to be impracticable. The lack, 
therefore, of any practicable unit, whether of ,weight or surface, by 
which to compare the solid substances used, made it best to content © 
ourselves with a rough qualitative method. 
In general, the most marked results seemed to follow when filter 
paper or starch grains were used. Whether this is due to the porous — 
structure and consequently immensely enlarged surface, cannot here 
be discussed. 
Another point of interest in this connection concerns the nature 
of the contact between the solution and the solid body. In all cases 
except that of paraffin the solution is capable of wetting the surface _ 
of the solid, thus bringing the molecules of solute and solvent into 
closest relation with the adsorbing surface. In the case of paraffin 
the situation is different. The solution is not capable of wetting - 
the paraffin even when in as close contact as can be obtained. As@ 
result, a surface of quite another sort is formed, more nearly com- = 
parable in some ways to that bounding the surface of the solution e 
where it comes in contact with the air. me 
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