Macleod.- — Rate of Oxiddlton of An'fahlcJi ijde to Acetic Acid. 37 



the aldehyde showed a decided decrease in excess of the oxygen it was 

 assumed that polymerization had taken place, probably on accomit of 

 traces of impurity in the vessel, and the experiment repeated The terra h' 

 was therefore neglected, thus greatly simplifying the equation, and introduc- 

 ing no great error. The work of calculating the results when ¥ is in- 

 cluded is extremely laborious, and little is illustrated when once the 

 principle of the action has been determined. The greatest error due to this 

 will probably be noticed most in the final values of the constant, because 

 there the pressure of the aldehyde is small, and an error of 4 or 5 mm. will 

 be most felt. 



General Discussion of the Equation used. 



The equation for the direct oxidation of the aldehyde to acetic acid 

 can be written either as 



2C2H,0 +02 = 2C2H4O2, or 



CsH.O + = CoH.Oa, 



in the second case the assumption being that the action goes on between 

 the oxygen atoms and the aldehyde molecules. 



If the first equation were the correct representation, the action should 

 proceed at a rate proportional to the square of the concentration of the 

 aldehyde and to the pressure of the oxygen. The second equation suggests 

 that the action proceeds at a rate proportional to the concentration of the 

 aldehyde and to the oxygen atoms. 



Everything points to the second equation being the correct one. The 

 values of K' worked out by this equation give, on the whole, good results, 

 and although there seems to be disquieting differences between some experi- 

 ments carried out under apparently the same conditions, yet this is probably 

 due to there being some catalytic agent present affecting the action. For 

 each experiment the value of K' obtained is fairly consistent, and the ex- 

 periments as a whole show a general consistency. 



The equation used was practically the same as that of Dr. Ewan, except 

 that h', the factor allowing for the aldehyde dissolved in the acetic acid 

 formed, was not taken into account. 



Let the partial pressure of aldehyde at the commencement of the experi- 

 ment be A millimetres, that of oxygen B millimetres, and that of nitrogen 

 N millimetres. P is the total pressure of the gas at any instant. Suppose 

 that after T minutes x millimetres of oxygen have combined with 2x milli- 

 metres of aldehyde to form acetic acid. The pressure of oxygen will then 

 be (& — x) and that of aldehyde (a — 2x). Also, there will be a certain 

 pressure of acetic-acid vapour, which will be equivalent to the vapour- 

 pressure of acetic acid at that temperature after the acetic acid formed 

 has commenced to condense to liquid. 



If, then, the action proceeds with a velocity proportional to the concen- 

 tration or pressure of aldehyde and of the oxygen atoms, then 



where j)' — partial pressure of oxygen, 



^2 = partial pressure of aldehyde, 



-jr = rate of change of pressure of oxygen. 



