Physiology. — “On the adsorption of odorous molecules to the 
surface of solids.” By Prof. H. ZWAARDEMAKER. 
(Communicated at the meeting of February 22, 1920). 
In the meeting of 24 May 1907*) I pointed out that in many 
cases a prolonged and marked adsorption of odorous molecules to 
solid bodies takes place, as soon as their surfaces have come into 
contact with gases that are mixed with odorivectors*). The simple 
act of opening a bottle filled with valerianie acid suffices to cover 
all the objects in a large room with valerianic acid molecules, so 
that when rubbing their surfaces with a dry wad of cottonwool, 
the latter is sure to give off a smell of valerianic acid. Even the water 
in which glass objects are washed that were in such a room, 
distinctly betrays the presence of odorous matter in a subsequent 
spraying under overpressure of two atmospheres and when studying 
the vapour electricity ensuing from it. *) 
The occurrence of these adsorptions depends chiefly on the presence 
of a condensation layer of air and watervapour on all surfaces. *) 
Besides, there is a possibility of a direct adsorption to surfaces from 
which this condensation layer has been purposely removed. Finally 
adsorption may occur to electrically charged surfaces, which attract 
particularly the particles of opposite sign that are present in the air. 
We will call the various forms of adsorption to the surfaces of 
solid bodies adsorptions of the 18*, 2™¢ and 3td sort. 
Those of the first sort comprise nearly all common cases of ad- 
sorption of odorivectors to solid surfaces. 
Those of the second sort are very rare. Strictly speaking they 
occur only on cleansed surfaces of amber, sulphur or paraffin, on 
which the condensation layer may be missing, and which consequently 
are excellent insulators for static electricity. 
1) Kon. Akad. v. Wetensch., Amsterdam, Proc. June 29 1907. This investigation 
has afterwards been extended by J. HERMANIDES, see Onderz. Physiol. Lab. Utrecht 
(5) 1909 X. bl. 28. Also H. ZwAARDEMAKER in Tigerstedt’s Hdb. der Physiol. 
Method. Bd Ill, p. 49. CG. van Dam, Arch. neerl. de Physiol. t. 1. p. 664, 1917, 
A. Heyninx, Essai d’Olfactique physiologique, Bruxelles 1919, p. 82. 
2) A. HEYNINX, l.c, p. 19. 
3) H. ZWAARDEMAKER, Arch. neerl. de Physiol. t. 1. p. 347. 1917. 
4) Bunsen, Wiedemann’s Annalen, Bd 24, p. 321, 1885. 
