14 THE ATOMIC WEIGHTS. 



bulbs, and finally through a system of driers containing successively 

 calcium chloride, sulphuric acid, and phosphorus pentoxide. The water 

 formed by the combustion was collected in a condensing tube connected 

 with a U tube containing phosphorus pentoxide. The latter was fol- 

 lowed by a safety tube containing either calcium chloride or phosphorus 

 pentoxide, added to the apparatus to prevent reflex diffusion. Full 

 details as to the arrangement and construction of the apparatus are 

 given. The final results appear in three series, representing jthe three 

 sources from which the hydrogen was obtained. All weights are cor- 

 rected to a vacuum. 



First Series. Hydrogen from Zinc and Acid. 



Wt. of H. Wt. H.,0. At. Wt. O. 

 .4233 3-8048 15.977 



.4136 3-7094 15.937 



.4213 3-7834 15-960 



.4163 3.7345 15.941 



.413' 3-7085 15-954 



Mean, 15.954, rh .0048 



Second Series. Electrolytic Hydrogen. 



.4112 3-6930 15.962 



.4089 3.6709 15-955 



4261 t , 3.8253 15-955 



4197 3-7651 15-942 



4H4 3.7I97 J 5-953 



Mean, 15.953, =h .0022 



Third Series. Hydrogen from Aluminum. 



.42205 3.7865 15.943 



.4284 3-8436 15-944 



.4205 3-7776 15.967 



43205 3-8748 15.937 



.4153 3-7281 15.954 



.4167 3-7435 15-967 



Mean, 15.952, .0035 

 Mean of all as one series, 15.953, =t .2O 



Shortly after the appearance of this paper by Cooke and Richards 

 Lord Rayleigh pointed out the fact, already noted by Agamennone, that 

 a glass globe when exhausted is sensibly condensed by the pressure of 

 the surrounding atmosphere. This fact involves a correction to the fore- 

 going data, due to a change in the tare of the globe used, and this cor- 

 rection was promptly determined and applied by the authors.* By a 



* Proc. Atner. Acad., 23, 182. Am. Chem. Journ., 10, 191. 



