.NFaci-kod. — lUiiv of Oxidation of ArffaldcJiydc to Acetic Acid. 35 



Method op Procedure. 



In each experiment the mercury was first brought up to the tap K, the 

 limb opening to the air being free. The tap wae then closed, and the 

 barometer and vessel lowered until the mercury in the barometer-tube 

 was below the level of the tap K. The liquid aldehyde was then intro- 

 duced into the vessel C, and the tap closed from the apparatus. The 

 tube M was then connected with a vacuum pump, and with the tap D turned 

 to connect all the ways with B the whole was evacuated. The tap B was 

 then closed, and K turned to connect the mercury with , the apparatus. 

 Aldehyde was then allowed to distil into the reaction-vessel, which it did 

 very readily, the mercury all the time being kept as near to K as possible. 

 The vessel was then evacuated again, and this repeated three or four times, 

 so as to completely replace the air by aldehyde. The final pressure of the 

 aldehyde was taken, and the tap D turned so as to disconnect the right- 

 hand part of the vessel, the reaction-vessel being only connected with the 

 capillary tubing DLK The tap K was also closed. The capillary tubing 

 DBM was then evacuated by means of the pump, and the tap B closed. 

 M was then connected with a tube delivering pure oxygen dried over 

 calcium-chloride. If the total pressure in the reaction-vessel was not re- 

 quired to be more than atmospheric pressure, the tap D was opened so as to 

 connect all three ways, and, as soon as the oxygen had entered, the tap D 

 was again turned, so as only to connect the tube DNK with the reaction- 

 vessel, and the pressure read off. The tubing DB thus did not form part 

 of the reaction-vessel. 



If the pressure in the reaction- vessel was required to be greater than 

 atmospheric pressure, the tap D was first turned so as to connect the tube 

 DNK with the tube DB and disconnect the vessel A containing aldehyde. 

 The mercury L was then lowered and the tap K turned. Oxygen was thus 

 drawn over into the pipette J without aldehyde. The tap D was then 

 turned to connect the vessel A with the pipette J, and the mercury head 

 raised, driving the oxygen back into the reaction-vessel A. In this way 

 any pressure obtainable on the gauge could be obtained in the reaction- 

 vessel. The volume, also, not at the temperature of the bath was only that 

 of the capillary tubing DNK. 



At the end of each experiment the capillary tubing BD was first 

 evacuated, and the tap B closed. Sodium-hydrate solution of known 

 specific gravity was then allowed to fill the capillary tube. The vessel 

 containing the hydrate was then weighed and again placed under B, the 

 taps B and D being turned so as to let the hydrate into the reaction-vessel. 

 The beaker containing the hydrate was again weighed, and the loss was 

 that due to the hydrate drawn in. In this way the capillary tubing BD 

 was filled with hydrate before both the first and second weighing, and hence 

 introduced no error. 



In the case where the final pressure in the reaction-vessel was greater 

 than atmospheric pressure, the pressure was diminished by lowering the 

 mercury head, and drawing some of the gas over into the pipette J, and 

 finally driving it back when the hydrate had been introduced. The hydrate 

 in a few minutes polymerized the whole of the aldehyde remaining, as the 

 pressure soon became constant. Allowance had to be made for the vapour- 

 pressure of the hydrate let in in determining the final pressure of oxygen. 



When the whole of the aldehyde had been polymerized, the tap D was 

 turned to disconnect DB, and a portion of the remaining oxygen and 



2* 



