APPENDIX III. 495 



confirmed by four observed positive properties possessed by it, which 

 are: 



1. The spectrum of argon observed by Crookes under a low pressure (in 

 Geissler-Pliicker tubes) distinguishes it; from other gases. 7 It was proved 

 by this means that the argon obtained by means of magnesium is identical 

 with that which remains after the uconversion of the atmospheric nitrogen 

 into nitric acid. Like nitrogen, argon presents two spectra produced at 

 different potentials of the induced current, one being orange-red, the other 

 steel-blue ; the latter is obtained under a higher degree of rarefaction and 

 with a battery of Leyden jars. Both the spectra of argon (in contradistinction 

 to those of nitrogen) are distinguished by clearly defined lines. 8 The red 

 (ordinary) spectrum of argon has two particularly brilliant and characteristic 

 red lines (not far from the bright red line of lithium, on the opposite side to 

 the orange band) having wave-lengths 705*64 and 696*56 (see Vol. I., 

 p. 565). Between these bright lines there are in addition lines with wave 

 lengths 603*8, 565*1, 561*0, 555*7, 518*58, 516*5, 450*95, 420*10, 415*95 and 

 394*85. Altogether 80 lines have been observed in this spectrum and 119 in 

 the blue spectrum, .of which 26 are common to both spectra. 9 



2. According to Rayleigh and Ramsay the solubility of argon in water 

 is approximately 4 volumes hi 100 volumes of water at 13. Thus argon 

 is nearly 2 times more soluble than nitrogen, and its solubility ap- 

 proaches that of oxygen. Direct experiment proves that nitrogen obtained 

 from air from boiled water is heavier than that obtained straight from the 

 atmosphere. This again is an indirect proof of the presence of argon in 

 air. 



3. The ratio & of the two specific heats (at a constant pressure and at 



7 The greatest brilliancy of the spectrum of argon is obtained at a tension of 9 mm., 

 while for nitrogen it is about 75 mm. (Crookes). In Chapter V., Note 16 bis, it is said 

 that the same blue line observed in the spectrum of argon is also observed in the spectrum 

 of nitrogen. This is a mistake, since there is no coincidence between the blue lines of 

 the argon and nitrogen spectra. However, we may add that for nitrogen the following 

 moderately bright lines are known of wave-lengths 585, 574, 544, 516, 457, 442,^36, and 

 426, which are repeated in the spectra (red and blue) of argon, judging by Crookes' 

 researches (1895) ; but it is naturally impossible to assert that there is perfect identity 

 until some special comparative work has been done in this subject, which is very desirable, 

 and more especially for the bluish-violet portion of the spectrum, more particularly 

 between the lines 442-436, as these lines are distinguished by their brilliancy in both the 

 argon and nitrogen spectra. The above-mentioned supposition of argon being polymerised 

 nitrogen (N 3 ), formed from nitrogen (N 2 ), with the evolution of heat, might find some 

 support should it be found after careful comparison that even a limited number of 

 spectral lines coincided. 



8 At first the spectrum of argon exhibits the nitrogen lines, but after a certain time 

 these lines disappear (under the influence of the platinum, and also of Al and Mg, but 

 with the latter the spectrum of hydrogen appears) and leave a pure argon spectrum. It 

 does not appear clear to me whether a polymerisation here takes place or a simple 

 absorption. Perhaps the elucidation of this question would prove important in the 

 history of argon. It would be desirable to know, for instance, whether the volume of 

 argon changes when it is first subjected to the action of the electric discharge. 



9 Crookea supposes that argon contains a mixture of two gases, but as he gives no 

 reasons for this, beyond certain peculiarities of a spectroscopio character, we will not 

 consider this hypothesis further. 



