352 



LORI) RAYLEIGH ON THK COMPRESSIBILITY OF (JASKS 



The deviations from unity in the cases of oxygen and argon were thought to exceed 

 the terrors of observation. The results presently to be given for oxygen render it 

 probable that the larger half of the deviation was, in fact, error. At any rate, 

 BOYLK'S law was sensibly observed by air, hydrogen and carbonic oxide. 



The method employed in this research appeared to be satisfactory, and I was 

 desirous of extending it to higher pressures, still, however, below the atmospheric, as 

 to which there seemed to be a great dearth of information. I could find only some 

 incidental observations by AMAGAT'" on air and carlxmic acid, and these it may be 

 well to quote : 



The pressures were as 2:1, and the "initial pressure" > was the smaller. The 

 temperature was from 17 C. to 19 C. The ratio pvjp'tf is what I have denoted 

 by B. It will be seen that the numbers for air exhibit considerable discrepancies. 



The earlier entries in AMAGAT'S table correspond pretty closely with the observa- 

 tions that I proposed to undertake. Besides the general elucidation of the behaviour 

 of gases at reduced pressures, the object in view was to obtain material for comparing 

 the densities of various gases at great rarefactions. Iu the actual weighings of gases 

 the pressure in the containing vessel is usually atmospheric, but the ratios of densities 

 so obtained are not immediately available for inferring molecular weights according to 

 AVOGADRO'S rule. This rule can only be supposed to apply with rigour when the 

 gases are so far rarefied as to come within the range of BOYLE'S law.t For this 

 purpose it is advisable that the range of pressure employed should be suilicient to 

 give accuracy, but not so high that the application to AVOGADKO'S rule involves too 



* Ann. de Chimie, 1 tome xxviii., 1 883. 



t The application of this idea to oxygen and hydrogen was made in my paper " On the Relative 

 Densities of Oxygen and Hydrogen," 'Roy. Soc. Proc.,' vol. 50, p. 448, 1892; 'Scientific Papers,' vol. 3, 

 p. 525. My hesitation then and later to push the investigation further, so as to obtain corrections to the 

 relative densities observed at atmospheric pressure, arose from the uncertainties in which the anomalous 

 observations of MEXDELEEF and SII.JERSTUOM had enveloped the behaviour of gases at low pressures-. 



