498 PRINCIPLES OF CHEMISTRY 



properties in the liquid and critical states, which almost 13 disposes of the sup- 

 position that it contains a mixture of two or more unknown gases. As the 

 first experiments showed, argon remains a gas under a pressure of 100 

 atmospheres and at a temperature of 90 ; this indicated that its critical 

 temperature was probably below this temperature, as was indeed found to 

 be the case when the temperature was lowered to 128'6 14 by means of 

 liquid ethylene. At this temperature argon easily liquefies to a colourless 

 liquid under 38 atmospheres. The meniscus begins to disappear at between 



13 There only remains the very remote possibility that argon consists of a mixture of 

 two gases having very nearly the same properties. 



14 The following data, given by Olszewsky, supplement the data given in Chapter II., 

 JNote 29, upon liquefied gases. 



(tc) (pc) t , s 



N 2 -146 85 -194-4 -214 0'885 



CO -139'5 85-5 -190 -207 ? 



A -121 60-6 -187 -189'6 1-5 



O 2 -118-8 60-8 -182'7 ? T124 



NO - 93'5 71-2 -153'6 -167 ? 



CH 4 - 81'8 54-9 -164 -158'8 0'415 



where tc is the absolute (critical) boiling point, pc the pressure (critical) in atmospheres 

 corresponding to it, t the boiling point (under a pressure of 760 mm.), t\ the melting point, 

 and s the specific gravity in a liquid state at t. 



The above shows that argon in its properties in a liquid state stands near to oxyge^ 

 (as it also does in its solubility), but that all the temperatures relating to it (tc, , and < t ) 

 are higher than for nitrogen. This fully answers, not only to the higher density of argon, 

 but also to the hypothesis that it contains N 3 . And as the boiling point of 'argon differs 

 from that of nitrogen and oxygen by less than 10, and its amount is small, it is easy to 

 understand how Dewar (1894), who tried to separate it from liquid air and nitrogen by 

 fractional distillation, was unable to do so. The first and last portions were identical, 

 and nitrogen from air showed no difference in its liquefaction from that obtained from 

 its compounds, or from that which had been passed through a tube containing incandescent 

 magnesium. Still, it is not quite clear why both kinds of nitrogen, after being passed 

 over the magnesium in Dewar's experiments, exhibited an almost similar alteration in 

 their properties, independent of the appearance of a small quantity of hydrogen in them. 



Concluding Remarks (March 81, 1895). The ' Comptes rendus ' of the Paris 

 Academy of Sciences of March 18, 1895, contains a memoir by Berthelot upon the reaction 

 of argon with the vapour of benzene under the action of a silent discharge. In his ex- 

 periments, Berthelot succeeded in treating 83 per cent, of the argon taken for the 

 purpose, and supplied to him by Ramsay (37 c.c. in all). The composition of the product 

 could not be determined owing to the small amount obtained, but in its outward 

 appearance it quite resembled the product formed under similar conditions by nitrogen. 

 This observation of the famous French chemist to some extent supports the supposition 

 that argon is a polymerised variety of nitrogen whose molecule contains N 3 , while ordinary 

 nitrogen contains N 2 . Should this supposition be eventually verified, the interest in 

 argon will not only not lessen, but become greater. For this, however, we must wait for 

 further observations and detailed experimental data from Rayleigh and Ramsay. 



The latest information obtained by me from London is that Professor Ramsay, by 

 treating cleveite (containing PbO, TJOj, Y 2 O 3 , &c.) with sulphuric acid, obtained argon, 

 and, judging by the spectrum, helium also. The accumulation of similar data may, after 

 detailed and diversified research, considerably increase the stock of chemical knowledge 

 which, constantly widening, cannot be exhaustively treated in these 'Principles of 

 Chemistry,' although rery probably furnishing fresh proof of the 'periodicity of the 

 elements.* 



