108 



DENSITIES I'K ()\•^(;l•■\• AND llVDIiUUEN 



The saiDe oljservations were then repeated after say 

 ten (lays; if in* tliminution uf pressure was noticed, 

 the experiment was continued say fifty or ;i liundred 

 (lays, when the final readings were made. In order ti> 

 leduce the indications of pressure to weight, in one of 

 these experiments, we need to know the approximate 

 volume of the oxygen and tlie ajiitroximate height of 

 tile cnlumn iif nu'iviny. Tlic first was estimated from 

 th(- (•a|)acity of the tube; which suttices for a dirt'erential 

 observation. The height of the nieivury was measured 

 witli a woollen metre. Correcting the observed pies- 

 Fig. 40.— Apparatus for detecting ab- sures for the temperatuvc of the mercurial cohimn, we 



sorption of oxygen by phosphorus 

 pentoxide ; set up for the ex- 



liave the results given below. 



periment. 



October 17 



" 27 

 December 25 



" 27 



Temperature of Oxygen. 

 18.06" 

 18.20" 

 18., 5° 

 18.16° 



Pressure. 

 842. 10 mm. 

 841.97 



842.02 " 



842.03 " 



W.j.^l.l. 



•'4S5 Kr. 

 .1484 " 



.1-184 ' 



.1484 



In this sam-ple, therefore, no apprecial)le absorption of o.xygen by lower 

 oxides of phosphorus was to be feared in the conditions in whicli the tubes weie 

 used. 



The precaution is Ijy no means unneces.sary, as a somewhat troublesome 

 mishap showed. 



The result is of interest as confirming Kegnault's o]iinion that oxygen does not 

 act on mercuiy at ordinary temi)eiatures.* Tlie contrary oi)inion is sometimes 

 attiibuted to him. My obsei'vations, extending over some months, agree perfectly 

 witli his opinion. 



IB. 



-SYNTIIKSIS OF AVATER. 



DATA OF EXI'EUniENTS. 



The two following tal)]es give the results of the exj)eriiiu'nts. In Table 1. 

 are given the volume of the gas extracted after the ctmibustion, with its composi- 

 tion ; the weight of the hydrogen ; and the weights of the oxygen found, of the 



* Mi'moires dc r Acadi'mic^ 26, 237. 



