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Transactions. 



unless constantly rectified. Both of these difficulties were overcome by 

 using a tap K, by means of which the mercury was shut off from contact 

 with the aldehyde and oxygen, except for a few seconds while a reading 

 was being taken. The tap K was a three-way tap the other limb con- 

 necting with the air. 



The volume of the reaction-vessel thus remained constant, and the 

 reaction could be allowed to proceed an indefinite time without further 

 attention. The readings were always taken with the mercury just up to 

 the tap. The tap used was of the Geissler form, this form being the best 

 able to prevent leakage. 



A^second modification was made by putting an ordinary three-way tap 

 at D. This was useful for several reasons. At the end of each experiment 

 the whole of the hydrate solution was allowed to run in through the tap B. 

 The three-way tap D could be so turned as to prevent the hydrate running 

 along to the tap K, and so on to the mercury. The aldehyde was contained 

 in a vessel C, with a tap C. B is a single tap through which the oxygen 

 was introduced. H is a mercury seal covering the junction of the pipette 

 J with the mercury manometer. G is a trap to prevent air reaching the 

 apparatus, if any should happen to leak through the indiarubber tubing. 

 E is a barometer-tube, the lower constricted part of which dips under the 

 mercury in L. The vessel L and the barometer-tube E could be moved 

 up and down. The pressure in the vessel was thus obtained by reading 

 the difference in height between K and E. 



