258 



Prof. J. Dewar. 



[Mar. 9, 





0. 



nr. 



H. 



CO. 



Arg. 





21-21 



25 '49 



24-18 









21 -50 



23 -6 











20 '8 



25-0 











20 -30 



24-04 





24 : 54 



20-34 





20 *90 



25 -80 





26 -04 



21 -30 



Baly, W.-Mallet 



19 -68 



24 58 





23 -94 



23 -52 



W.-Mallet, for H 







22-90 







W.-Mallet, for H 







22 -62 













23 -12 







The two Waterston-Mallet results for hydrogen are of importance as 

 showing that even great variations in the value of A affect but little 

 the zero molecular volume. It is further to be remarked that the 

 hydrogen results claim precedence over the others because they have 

 been obtained from observations extending down to some 14° absolute. 

 Moreover, the value 24-18 for hydrogen has been got directly from 

 experiment, whilst the other values have been obtained from semi- 

 theoretical equations whose validity is subject to some doubt. 



5. With these values for the molecular volumes at absolute zero of 

 oxygen, nitrogen and hydrogen, namely 21*21, 25*49 and 24" 18 respec- 

 tively, and knowing that the molecular volume of ice at absolute zero 

 is 19-21 and of carbonic acid is 25*7 as deduced from a study of the 

 coefficients of expansion at low temperatures,* we can find the con- 

 traction or expansion on the assumed hypothetical production of these 

 compounds from their elements at the zero of temperature. 



Thus 100 volumes of mixed solid hydrogen and oxygen become 

 after combination 55*22 volume of ice, or there is a contraction of 

 45 per cent. This is of the same order of magnitude as for N 2 and 

 Li 2 0, whose contraction from solid oxygen, solid nitrogen and metal 

 amounts to 60 per cent. On the other hand the production of carbonic 

 acid from diamond (V = 6*82) or graphite (V = 10*44) and solid oxygen 

 gives in the former case a slight expansion of 44 per cent., but in the 

 latter case a slight contraction of 3 per cent. 



The case of carbonic oxide (V = 24*5) is interesting; produced from 

 diamond and oxygen it expands by 74| per cent., and from graphite and 

 oxygen it expands by 54f per cent., but on the addition of another 

 atom of oxygen the resulting product, carbonic acid, undergoes a con- 

 traction of 27 per cent. 



6. Berthelotf made a minute examination of the values of d(j>v)/dp in 

 reduced co-ordinates for eight substances whose critical temperatures 



* " Coefficients of the Cubical Expansion of Ice, Hydrated Salts, Soluble 

 Carbonic Acid, and other Substances at Low Temperature," 'Roy. Soc. Proc.,' 

 vol. 73. 



f " Sur les Thermometres a gaz. Trav. et Mem. Poids et Mesures," vol. 13. 



