1896.] More about Argon. ' 3 



disappeared from the spectrum of the jar discharge.* After a little 

 more sparking, a satisfactory weighing was obtained on May 22, 

 1895 ; but, in attempting to repeat, a breakage occurred, by which a 

 litre of air entered, aad the whole process of purification had to be 

 recommenced. The object in view was to effect, if possible, a series 

 of weighings with intermediate sparkings, so as to obtain evidence 

 that the purification had really reached a limit. The second attempt 

 was scarcely more successful, another accident occurring when two 

 weighings only had been completed. Ultimately a series of four 

 weighings were successfully executed, from which a satisfactory con- 

 clusion can be arrived at. 



May 22 „ 3-2710 



June 4 3-2617 



June 7 3-2727 



June 13 3-2652 



June 18 3-2750) 



June 25 3-2748 3-2746 



July 2 3-2741) 



The results here recorded are derived from the comparison of 

 the weighings of the globe " full " with the mean of the preceding 

 and following weighings " empty," and they are corrected for the 

 errors of the weights and for the shrinkage of the globe when 

 exhausted, as explained in former papers. In the last series, the 

 experiment of June 13 gave a result already known to be too low. 

 The gas was accordingly sparked for fourteen hours more. Between 

 the weighings of June 18 and June 25 there was nine hours' spark- 

 ing, and between those of June 25 and July 2 about eight hours' 

 sparking. The mean of the last three, viz. 3-2746, is taken as the 

 definitive result, and it is immediately comparable with 2-6276, the 

 weight under similar circumstances of oxygen.f If we takeOa = 16, 

 we obtain for argon 



19-940, 



in very close agreement with Professor Ramsay's result. 



The conclusion from the spectroscopic evidence that the gases 

 isolated from the atmosphere by magnesium and by oxygen are 

 essentially the same is thus confirmed. 



The refractivity of argon was next investigated, in the hope that 

 it might throw some light upon the character of the gas. For this 



* Jan. 29. — When the argon is nearly pin-e, the arc discharge (no jar connected) 

 assumes a peculiar purplish colour, quite distinct from the greenish" hue apparent 

 while the oxidation of nitrogen is iu progress and from the sky blue observed 

 when the residue consists mainly of oxygen. 



t Roy. Soc. Proc. vol. 53, p. 144, 1893. 



b2 



