144 



Lord Rayleigh. 



[Mar. 23, 



lowest 2-6266, mean 2-62691. In the second set (June, July, 1892) 

 the highest result was 2'6273 and the lowest 2'6267, mean 2*62693. 



The second method (6) proved very convenient, the evolution of gas 

 being under much better control than in the case of chlorates. The 

 recrystallised salt was heated in a Florence flask, the wash-out, in 

 this case also, being facilitated by a vacuum. Three fillings gave 

 satisfactory results, the highest being 2-6273, the lowest 2-6270, and 

 the mean 2 '62714. The gas was quite free from smell. 



By the third method I have not as many results as I could have 

 wished, operations having been interrupted by the breakage of the 

 electrolytic generator. This was, however, of less importance, as I 

 hal evidence from former work that there is no material difference 

 between the oxgen from chlorates and that obtained by electrolysis. 

 The gas was passed over hot copper, as detailed in previous papers. 

 The result of one filling, with the apparatus as here described, was 

 2-6271. To this may be added the result of two fillings obtained at 

 an earlier stage of the work, when the head of the manometer was 

 exhausted by an independent Sprengel pump, instead of by the 



Toppler. The value then obtained was 2*6272. The results stand 

 thus : — 



Electrolysis (2), May, 1892 2-6272 



(1) „ 2-6271 



Chlorates (5), May, 1892 2-6269 



(5), June, 1892 2'6269 



Permanganate (3), January, 1893 » . 2-6271 



Mean 2-62704 



Correction for contraction . . 0'00056 



2-62760 



It will be seen that the agreement between the different methods is 

 very good, the differences, such as they are, having all the appearance 

 of being accidental. Oxygen prepared by electrolysis is perhaps 

 most in danger of being light (from contamination with hydrogen) , 

 and that from chlorates of being abnormally heavy. 



Nitrogen. 



This gas was prepared, in the usual manner, from air by removal 

 of oxygen with heated copper. Precautions are required, in the first 

 place, to secure a sufficient action of the reduced copper, and, 

 secondly, as was shown by v. Jolly, and later by Leduc, to avoid 

 contamination with hydrogen which may be liberated from the copper. 

 I have followed the plan, recommended by v. Jolly, of causing the 

 gas to pass finally over a length of unreduced copper. The arrange- 

 ments were as fo^ows : — 



