Approximate values of some contact angles

Contact angles and molecular orientation at solid surfaces. 

Just as the work of adhesion between two liquids (Chap. IV, 2) gives information as to the orientation of molecules of an organic liquid in contact with water, so WSL, deduced by (3) from the contact angle, may indicate the orientation of the surface molecules in a solid. The problem is easier in one respect, for the surface molecules of a solid are not in constant motion with changes of orientation, as are those of a liquid. On the other hand, the soaking of the liquid into the surface layers of the solid may confuse the results in a way not likely to occur with the liquid surface also the surface of the solid may be difficult to clean. This last difficulty has, in the author s experience, proved surprisingly small. 

A long chain iodide gave the same high angle when cut as on the naturally solidified surfaces this is in accord with the known low adhesion of organic halides for water. Cut surfaces of paraffin wax showed the same angle as the natural surfaces. 

An attempt was made to obtain a surface with all the water-attracting groups oriented outwards, by crystallizing the acids on a water surface. This failed, probably because the lowest layer of molecules next the water, although it probably was oriented with the hydrophilic groups to the water, stuck to the water instead of to the solid cake when this was removed. The adhesion between the carboxyl ends of the molecules of this 

Contact angles with two liquids and a solid. The mathematical treatment of the case of two liquids A and J5, and a solid St is similar to 

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