Mr. Ivory on the Constitution of the Atmosphere. 197 



point, and compare them with those afforded by observation, 

 we obtain the following table : — 



Boiling point C. 



Calculated. Observed. 



C* H'OS 73 Regnault. 



C^H^CFS 73 + 8-12 = 169 160 



C^H'tCl'* 30-5 ... 



C^H^Cl*^' 30-5 +2-12 =54-5 60'8 ... 



C2 CIS 30'5 + 4-12 =78-5 78-0 ... 



But, as I havealieady stated, too much uncertainty prevails 

 respecting the boiling points to allow of our determining the 

 numbers in a law with absolute accuracy : the existence of 

 a law of the form which has been proposed is beyond doubt. 



When the specific volumes of a bodj' are known for all 

 temperatures, those of an analogous compound always diflFer 

 by a constant magnitude, and the knowledge of the specific 

 weight, and of the expansion of the first and of the specific 

 weight of the latter for any temperature, consequently gives 

 the expansion of the latter. 



It is scarcely necessary to call attention to the importance 

 of these laws ; they are tor the determination of the physical 

 properties of chemical compounds what the law of definite 

 proportions is for the knowledge of their constitution. 



XXIX. On the Constitution of the Atmosphere. Bif ih'i'i^^ 

 Ivory, K.H., M.A., Hon. M.R.I. A., Instit. Reg. Sc. Paris, 

 et Reg. Soc. Gotting. Con-esp.* 

 1 T is known that atmospheric air is a mixture of several 

 -* gases and of aqueous vapour. The quantity of aqueous 

 vapour amounts, at a maximum, only to an inconsiderable pro- 

 portion of the whole volume, and often to so small a propor- 

 tion as to be insensible in its effect. We may therefore, for 

 the sake of simplicity, suppose, in the first place, that the air 

 of the atmosphere contains no vapour of water, or is in a dry 

 state. The constituent gases of air, as far as they have been 

 estimated, are three, oxygen, azote, and carbonic acid, but as 

 this last never exceeds j^'jjjjth of the mixture, we may neglect 

 it and consider air as containing only oxygen and azote. 



Let us now take a portion of oxygen, one of azote, and one 

 of atmospheric air; p and 6 representing the pressure and 

 temperature common to all the three fluids; and their densi- 

 ties and volumes being respectively g, u ; g', u' ; and R, V. 

 We shall have, by the law of Mariotte, 



• Coinmuiiicatecl by tlie Author. 



