502 Sir W. Ramsay and Dr. B. D. Steele on the 



The error arising- from the determination of the volumes 

 in the tube A is negligible ; this is seen from the following 

 result of a calibration carried out in duplicate : — 



February 16th. Marcli oth. 



I. . . . 228-947 . . . n^'^&'2 



11. . . . 201-866 . . . 201-856 



III. . . . 179-473 . . . 179-463 



IV. . . . 156-399 . . . 156-379 

 v. . . . 114-734 . . . 114-742 



VI. . . . 95-171 . . . 95-167 



The temperature of the vapour-jacket can easily be main- 

 tained constant to within 0*02° bv occasionally adjusting the 

 pressure under which the liquid boils : this has been re- 

 peatedly tested and proved during the course of the research. 

 The temperature at which the majority of the experiments 

 were carried out w'as 130" ; the absolute temperature was 

 therefore about 403°, and a variation of 0*02° would therefore 

 amount to only 1 part in 20,000. 



The weighings were made with a long-beam Oertling's 

 balance which, on reading by oscillations, recovered weighings 

 correct to w^ithin 0*00002 gram ; duplicate weighings of one 

 of the toluene and of one of the methyl-alcohol bulbs will 

 serve to illustrate the accuracy that could be attained by 

 careful weighing : — 



Toluene. Metliyl-alcoliol. 



I. . . . 0-77528 gram 0-39244 gram 



11. . . . 0-77527 „ 0-39242 „ 



As, however, each experiment involved two weighings, one 

 of the full and one of the empty bulb, the total error was 

 probably about one twenty-fifth of a milligram, or 0-00004. 

 Since the average weio-bt of substance taken was about 

 0-15 gram the error should be about 1 in 4000; and this is 

 about the degree of concordance which has been found in 

 cases in which more than one experiment with the same 

 substance has been carried out. 



The Coefficient of Expansion of Oxygen, 



As already explained it was necessary to determine this 

 coefficient in order that the densities of the vapours might 

 be compared directly with that of oxygen. What was done 

 practically was to express the temperature of the experiment 

 in terms of an oxygen thermometer. 



