Farhow. — DepreKxioii of Frec-iiuj-jmint of Water. 33 



COXCLUSIONS. 



The results seem to indicate — 



(1.) That for a solution which is stirred while freezing the coefficient (i) 

 is less than 1 for the lower pressures, and, increasing with rise of pressure, 

 becomes greater than 1 at the higher pressures. 



(2.) That for solutions not stirred the coefRcient is always greater than 

 1. and increases with increasing pressure. 



The only quantitative result found amongst earlier work is given by 

 Garelli. He found that 0-35 grammes carbon-dioxide per 100 grammes 

 water gave a depression of 0-165° C. The author's value for the depression 

 at this concentration is 0-169° C, which agrees fairly well with that of 

 Garelli. 



Art. VII. — On the Bate of Oxidation of Acetaldehyde to Acetic Acid. 



By D. B. MACLEOD, M.A., Canterbury College. 



[Bead before the Philosophical Institute of Canterhury, 2nd November, 1910.} 



Introduction. 



In the 1894 number of the " Philosophical Magazine " an account is given 

 of some experiments made by Dr. T. Ewan on the rate of oxidation of 

 acetaldehyde to acetic acid, and the conclusion he comes to from his experi- 

 ments is that aldehyde is oxidized to acetic acid in the vaporous state 

 at a rate proportional to the concentration or pressure of the aldehyde 

 and to the square root of the oxygen-pressure This, however, did not 

 seem to apply when the pressure of oxygen was above 450 mm. of mercury 

 with the temperature at 20° C. In fact, he was unable to obtain any 

 evidence of action with an oxygen - pressure of 599 mm. even when the 

 temperature was 21-4° C. 



The peculiarity of this sudden cessation of action, and the small number 

 of the experiments of Dr. Ewan which are described, seemed to me to call 

 for more experiments, as he himself says, to clear up this interesting be- 

 haviour. No record of the work having been continued either by himself 

 or others could be found in the " Journal of the Chemical Society," the 

 " Philosophical Magazine," the " Transactions of the Royal Society," the 

 '' Journal of Physical Chemistry," or the " American Journal of Science." 



Description of Apparatus. 



The apparatus used was in principle the same as that of Dr. Ewan, 

 though with a few modifications, and is shown in the figure on the next 

 page. 



In Dr. Ewan's form of apparatus the mixture of aldehyde and oxygen 

 was left in contact with the mercury, thus necessitating the use of brom- 

 naphthalene to protect it, and also resulting in the volume of the reaction- 

 vessel changing as the pressure decreased, the mercury altering its position 



2— Trans. 



