46 



T raiisactioiii 



lutely, but, while little difficulty was experienced in drying the vessel and 

 oxygen by leaving them in contact with phosphorous pentoxide for a con- 

 siderable time, the same could not be done with the aldehyde. The most 

 effective drying agents are strongly basic or acidic oxides, or metals, such 

 as sodium and potassium, which show a strong affinity for water. 



Now, aldehyde is polymerized rapidly by mineral acids, bases, and many 

 salts. In fact, the utmost precautions must be taken to prevent polymeri- 

 zation, and the presence of the polymeric form, as has been shown, affects 

 the reaction. On this account attempts to obtain a perfectly dried sample 

 of aldehyde have so far failed. 



Could such an experiment be made, the result would probably show a 

 great retardation, if not a total cessation of the action. 



In view of the number of experiments quoted showing the influencing 

 effects of many substances on the speed of the reaction, little further support 

 is needed to affirm that the action is very sensitive to catalytic agents of 

 all kinds. The experiments of Dr. Ewan can, however, be further quoted 

 to support this. 



Four experiments, having their constants worked out, are recorded in 

 the " Philosophical Magazine." In the first experiment, with the tempera- 

 ture at 20° C, the value of K varies from 0-76 as a minimum to 1-27 as a 

 maximum. This is a very low value, for which he gives no explanation. 

 In the next experiment the value of K varies from 2-81 to 3-57 ; in the next 

 from 0-96 to 3-18 ; and in another experiment, in which the initial pressure 

 of oxygen was only 373 mm., well below his maximum, at which the reaction 

 goes on constantly, and the initial aldehyde pressure 178-5, the constant 

 begins at a maximum of 2-82, and falls rapidly to 2-59, and then to 2-34 — 

 in fact, in this experiment the reaction between the two last readings was 

 extremely slow, as will be shown by quoting the experiment : — 



It will be noticed that in the last eighty minutes the total pressure 

 fell only 5-7 mm., whereas in the latter part of a previous experiment, with 

 the oxygen-pressure at 409-1 mm. and the aldehyde pressure 119-1 mm., 

 the pressure fell 95 mm. in 700 minutes, although this latter case includes 

 pressures which should give a much slower rate on the average. 



For these variations Dr. Ewan gives no explanation. He mentions that 

 it seems of some importance to keep the apparatus as clean as possible, 

 but he does not say why. 



If we accept the idea that the action goes on between the aldeh}-de 

 molecules and the oxygen atoms, there are two separate actions the speed 

 of which catalytic agents could affect : there is, first, the breaking-up 

 of the oxygen molecule ; and, secondly, the combination of the aldehyde 

 with the oxygen atom. It seems to me most probable that in most cases 

 the first of these two actions is the one most aftected. Under the most 

 favourable conditions there could hardly be many atoms of oxygen present, 



