1904.] On the Density of Nitrous Oxide. 183 



the bottle still contained appreciable impurity is indicated by a weighing 

 on August 13, in which without liquid air the gas was drawn from the 

 top of the bottle. There appeared 



August 13 3-6354, 



about 1 milligramme short of the proper weight. 



It will be seen that the result without liquid air is almost identical 

 with that found by the same method in 1896, and that the further 

 purification by means of liquid air raises the weight only to 3 '6 365. 

 I find it difficult to believe that so purified the gas still contains 

 appreciable quantities of nitrogen. 



The corresponding weight of air being 2-3772,* we find that, referred 

 to air as unity, the density of nitrous oxide is 



3-6365 _ 1.5907 

 ~ 



Again, if oxygen be taken as 16, the density of nitrous oxide will be 



3-6365 x 16 _ 99 -, ,., 

 2-6276 ~ 



The excess above 22 is doubtless principally due to the departure of 

 nitrous oxide from Boyle's law between atmospheric pressure and a 

 condition of great rarefaction. I hope shortly to be in a position to 

 apply the correction which will allow us to infer what is the ratio of 

 molecular weights according to Avogadro's rule. 



* ' Koy. Soc. Proc.,' vol. 53, p. 134, 1893 ; ' Scientific Papers,' vol. 4, p. 47. 



VOL. LXXIV. 



