392 
DR. MEYER WILDERMAN ON CHEMICAL DYNAMICS 
air) first into the vessel behind, and then, about a quarter of an hour later, into the 
vessel in front. Both vessels were simultaneously exposed in the bath to the same 
acetylene light, but the velocity of combination of chlorine and carbon monoxide was 
considerably slower in the front vessel than in the vessel placed behind it. (The 
opposite would have been expected.) (See Curves 1 and 2 of Tables III. and IV.) 
The accelerating influence of water vapour upon the velocity of reaction is very 
great. The same glass bulb was filled with the chlorine and carbon monoxide, both 
freshly prepared in the dark. The chlorine was in both cases absolutely the same, 
i.e., equally dry; the freshly prepared carbon monoxide on the contrary was allowed 
to bubble in the two experiments through different heights of sulphuric acid in the 
bulb S (fig. 1, p. 340) by tilting the bulb more in the second experiment than in the 
first. The sulphuric acid was the same in both cases, and each time was first heated 
in the bulb in a vacuum till it was perfectly freed from any gas. The freshly-prepared 
carbon monoxide was thus most probably in one case a little drier than in the other, 
and the difference in the quantity of water still retained by the carbon monoxide 
evidently could only be exceedingly very small. The difference in the speed ol 
combination of carbon monoxide and chlorine on the contrary proved to be very great. 
(See curves of Table V.) 
A further experiment was thus made :—The gases were brought into the glass 
bulb containing ordinary concentrated sulphuric acid freed from air, well shaken, then 
left in the dark for about two days, and then exposed to the powerful acetylene 
light; no reaction could be observed after several hours during two days, but 
on exposure to sunlight the two gases combined, though only exceedingly slowly. 
Since the concentrated sulphuric acid was of sp. gr. P84, it contained water, and it 
must still have had (Regnault) a vapour pressure of water, though an extra¬ 
ordinarily small one, so that the pressure of water vapour was still not absolutely 
excluded, and this may be the cause why an exceedingly slow reaction could still take 
place in sunlight. 
Thus, the less water vapour is present with the gases the slower is the reaction. 
Reaction takes place in the presence of an exceedingly small quantity of water vapour 
in the mixture ; small, apparently immeasureable, differences in the amount of water 
vapour, at any rate when the vapour is present only in small quantities, produces 
great differences in the velocity of the reaction. 
It should be observed that we could not use greater quantities of water vapour for 
the experiments, still less could we have the gases in presence of water, because water 
decomposes the carbonyl chloride formed, giving carbonic and hydrochloric acids. 
Bunsen and Roscoe used their mixture of chlorine and hydrogen in the presence 
of water saturated with these gases. Piiingsheim found later on that, if chlorine 
and hydrogen are taken quite dry, they do not combine in light at all. This 
phenomenon Pringsheim thought possible to explain in the following manner :— 
The chlorine and hydrogen, according to his conception, do not combine directly to 
