ATOMIC VOLUMES. 287 



200 measures of oxygen form water ; 100 measures of 

 oxygen and 100 measures of vapour of sulphur form 

 sulphurous acid gas. Ammoniacal gas consists of 300 

 volumes of hydrogen and 100 volumes of nitrogen, con- 

 densed by combination into 200 volumes ; consequently, 

 we are enabled most readily to calculate the specific 

 gravity of ammoniacal gas. The specific gravity of 

 nitrogen is 0'9722, that of hydrogen 0'0694. Now, 

 three volumes of hydrogen are equal to 0'2082 : this 

 added to 0*9722 is equal to T1804, which is exactly the 

 specific gravity obtained by experiment. 



There is no doubt, from the generality with which 

 this law of volumes prevails, that it would be found to 

 extend through all substances, provided they could be 

 rendered gaseous ; in other words, there is abundant 

 proof to convince us that throughout nature the process 

 of combination, in the most simple ratio of volumes, is 

 in operation to produce all the forms of matte? known 

 to us. 



It has been shown, by the investigations of Dr. Dai- 

 ton, in 1840, that salts, containing water of crystalli- 

 zation, dissolve in water without increasing the bulk of 

 the fluid more than is due to the liquefaction of the 

 water which these salts contain ; while Joule and Play- 

 fair have shown that the anhydrous salts take up no 

 space in solution. From this we are naturally led to 

 conclude that the volume occupied by a salt in the solid 

 state has a certain relation to the volume of the same 

 salt when in solution, and has also a fixed relation to 

 the volume occupied by any other salt. The law appears 

 to be : the atomic volume of any salt whatever (an- 

 hydrous or hydrated) is a multiple of 1 !_, or of a number 

 near 11, or a multiple of 9 '8 (the atomic volume of ice), 

 or the sum of a multiple of 11 or 9 '8. Marignac, who 

 has also paid much attention to the subject, does not 

 think these numbers absolutely correct, but approxi- 



