ARGON, A NEW CONSTITUENT OF THE ATMOSPIIEKI':. 41 



There are many other lines of ai-gumeut whirh suggest tliemselves ; but we 

 think it will be acknowledged that tliose given above are sufficient to establish the 

 existence of argon in the atmosphere. 



It is practically certain that the argon prepai'ed by means of electric sparking 

 with oxygen is in the main identical with ai-gon [ti'cpaied by aid of magnesium. 

 The samples have in common : 



First: Spectra which alreatly have been shown to be identical as regards the 

 ten brightest lines. 



Second : They have approximately the same density. It is true that an actual 

 determination of the density of the sample prepared by sparking has not been 

 carried out ; but its density, determined indirectly, agrees with sufficient approxi- 

 mation with that found for the sam[)le prepared by means of magnesium. 



Third : The two samples have practically the same solubility in watei'. 



The question whether ai-gon is of an elementary or a compound nature is 

 settled according to the usually accei)ted theory by the I'atio of its specific heats in 

 favor of the former supposition. The argument may be stated thus: The kinetic 

 energv of a gas, due to the motion of its molecules, is proportional to the absolute 

 temperature. A rise of temperature increases the kinetic energy both of the 

 molecules as a whole, as well as of the atoms which are constituents of the 



molecules. If, howevei', the gas-molecule consists of a single at , inter-atomic 



motion wdthin the molecule is excluded, and the motion of the molecule through 

 space, oi- its ti'anslatioual motion, alone remains to be considered. The specific 

 heat at constant volume, C-^, of a gas whose molecules consist of free atoms corre- 

 sponds oidy to the energy due to theii' translation through space. The s])ecific 

 heat at constant pressure includes besides the heat equivalent of work done dui'ing 

 expansion. The work done by gases during expansion, howevei-, is practically 

 equal foi- all gases, seeing that their coefficients of expansion and compressibility 

 are practically the same. This quantity can easily be calculated to be 2.U0 caloi'ies 

 pel- gi-am-molecule for a pi-essure of 760 mm. and a rise of tempei-ature of 1° C. 



The ratio of the kinetic energy of a gas due to the translational motion of its 

 molecules to the tt)tal energy contained in the gas has been shown by Clausius ' to 

 be expi-essed by the equation 



K i (Cp - C.) 



H Gv 



where K is the energy of the moving molecules, and II the total energy contained 



^[Poggendorff's Annakn, 1857, 100, p. 377. 



