﻿526 



Dr. T. Ewan on the Rate of Oxidation 



are represented in the figure by circles. The theoretical 

 curve evidently represents these points with fair approximation. 

 It is interesting to notice that the whole curve here, up to 

 800 millim., corresponds to the part of the curve for phos- 

 phorus and dry oxygen between and 70 inillim. It would 

 be of interest to make experiments with sulphur and oxygen 

 at higher pressures in order to find out whether a maximum 

 velocity occurs similar to that found with phosphorus. 



Aldehyde and Oxygen. 



When, as in the experiments which have just been 

 described, the substance which is undergoing oxidation is a 

 solid or a liquid, its rate of evaporation becomes such an 

 important factor in determining the rate of the reaction, that 

 it is not easy to make out with perfect certainty what role is 

 played by the concentration of the oxygen. It appears, 

 however, very probable that in dry oxygen the rate of the 

 reaction is proportional to the square root of its concentration. 

 In order to further test the truth of this result, experiments 

 were made on the reaction between aldehyde-vapour and 

 oxygen. The reaction was found to go on with convenient 

 speed at 20°. As aldehyde boils at 21° under a pressure of 

 760 millim., it was assumed that aldehyde-vapour at 20° and 

 under pressures not exceeding 550 millim. might be regarded 

 with sufficient approximation as a perfect gas. Numerous 

 attempts were made to absorb the acetic acid formed, by 

 means of some solid substance without action on the aldehyde. 

 PbO, ZnO, BaC0 3 , KC 2 H 3 2 (anhydrous), were tried, but 

 they all appeared to cause a more or less rapid diminution in 

 the quantity of the aldehyde-vapour. The experiments were 

 therefore made without any such absorbent. 



The apparatus used (fig. 7) was essentially the same as that 

 which was employed by van't Hoff for the study of the forma- 

 tion of water from electrolytic gas (Etudes de dyn. chimique, 

 p. 53), and for the study of the decomposition by heat of PH 3 

 and AsH 3 . The reaction takes place in the bulb A (fig. 7) : this 

 has a capacity of 60 to 70 cubic centim., and is immersed in a 

 water- bath maintained at a constant temperature. The tubes 

 connecting A to the rest of the apparatus, which are not 

 plunged in the water, are made of capillary diameter in order 

 to diminish as far as possible the volume of gas which is at 

 the temperature of the air. The pressure of the gas in the 

 apparatus is determined by means of the manometer BCD. 

 By raising or lowering the tube C, the level of the mercury 



