1895.] Argon, a new Constituent of the Atmosphere. 273 



small. Thus, when a mixture of 5 c.c. of air with 7 c.c. of oxygen 

 was sparked for 1 hours, the residue was 0*47 c.c., and after removal 

 of oxygen 0'06 c.c. Several repetitions having given similar results, 

 it became clear that the final residue did not depend upon anything 

 that might happen when sparks passed through a greatly reduced 

 volume, but was in proportion to the amount of air operated upon. 



No satisfactory examination of the residue which refused to be 

 oxidised could be made without the accumulation of a larger quantity. 

 This, however, was difficult of attainment at the time in question. 

 It was thought that the cause probably lay in the solubility of the gas 

 in water, a suspicion since confirmed. At length, however, a suffi- 

 ciency was collected to allow of sparking in a specially constructed 

 tube, when a comparison with the air spectrum, taken under similar 

 conditions, proved that, at any rate, the gas was not nitrogen. At 

 first scarcely a trace of the principal nitrogen lines could be seen, but 

 after standing over water for an hour or two these lines became 

 apparent. 



V. Early Experiments on Withdrawal of Nitrogen from Air by means 

 of Red-hot Magnesium. 



A preliminary experiment carried out by Mr. Percy Williams on 

 the absorption of atmospheric nitrogen, freed from oxygen by means 

 of red-hot copper, in which the gas was not passed over, but simply 

 allowed to remain in contact with the metal, gave a residue of density 

 14*88. This result, although not conclusive, was encouraging ; and 

 an attempt was made, on a larger scale, by passing atmospheric 

 nitrogen backwards and forwards over red-hot magnesium from one 

 large gas-holder to another to obtain a considerable quantity of the 

 heavier gas. In the course of ten days, about 1500 c.c. were collected 

 and transferred gradually to a mercury gas-holder, from which the 

 gas was passed over soda-lime, phosphoric anhydride, magnesium at 

 a red heat, copper oxide, soda-lime, and phosphoric anhydride into 

 a second mercury gas-holder. After some days the gas was reduced 

 in volume to about 200 c.c., and its density was found to be 16*1. 

 After further absorption, in which the volume was still further re- 

 duced, the density of the residue was increased to 19*09. 



On passing sparks for several hours through a mixture of a small 

 quantity of this gas with oxygen, its volume was still further reduced. 

 Assuming that this reduction was due to the further elimination of 

 nitrogen, the density of the remaining gas was calculated to be 20*0. 



The spectrum of the gas of density 19'09, though showing nitrogen 

 bands, showed many other lines which were not recognisable as 

 belonging to any known element. 



