18 ARGON, A NEW CONSTITUENT OF THE ATMOSPHERE. 



In wi'ii^liiiii; the eun)ty gUibe, U.2 grainine was placed on tlie same pan as that 

 which liiuig from tlie eml of the beam to which it was suspended and the final 

 weight was adjusted by means of a ridei', or by small weights on the other pan. 

 This process practically leads to weighing by substitution of gas for weights. The 

 bulb was always handled wilii gloves, to avoid moisture or grease from tlie fingers. 



Three ex[)eriments, of which it is unnecessary to give details, were made to 

 test the degree of accuracy with which a gas could be weighed, the gas being dried 

 air, freed from carbon dioxide. The mean lesult gave for the weight of 1 litre of 

 air at 0°and 7(iO mm. pressui'e, 1.2935 gramme. Regnault found l.'2!:)34U, a correction 

 haviiic been applied by Crafts to allow foi- the estimated altei-ation of volume 

 caused by the contraction of his vacuous bulb. The mean result of detei'miuations 

 by several observers is 1.29347; while one of us found 1.29327. 



The globe was then filled with the carefully dried gas. 



Temperature, i8°.8o; pressure, 759. 3 mm. 



Weight of 162.843 c. c. of gas 0.21897 gramme. 



Weight of I litre gas at 0° and 760 mm i-43*'6 



Density, that of air compared with O = 16, being 14-476 16.100 



It is evident from these numbers that the deuse constituent of the air was 

 being concentrated. As a check, the bulb was pumped empty and agaiu weighed ; 

 its weiglit was 0.21903 gramme. This makes the density 16.105. 



It appeared advisable to continue to absorb nitrogen from this gas. The first 

 tube of magnesium lemoved a considerable quantity of gas ; the nitride was con- 

 verted into ammonium chloride, and the sample contained 66.30 p. c. of chlorine, 

 showing, as has before been remarked, that if any of the lieavier constituent of the 

 atmosi)here had been absorbed, it formed no basic compound wntli hydrogen. The 

 second tube of magnesium was hardly attacked ; most of the magnesiiun had 

 melted, and formed a layer at the lower i)art of the tube. That which was still 

 left in the body of the tube was black on the surface, but had evidtiutly not been 

 much attacked. The ammonium chloride which it yielded weighed only 0.0035 



gramme. 



The density of the remaining gas was then deteniiined. Hut as its volume 

 was oidv a little over 100 culiie centimetres, the bulb, the capacity of wliieli was 

 1(12 eul)ic centimetres, had to be filled at reduced pressure. This was easily done 

 by replacing the pear-shaped reservoir of the mercury gas-holder by a straight tube, 

 and noticing the level of the mercury in the gas-holder and in the tube which 

 served as a mercury reservoir against a giaduated mirror scale by help of a cathe- 

 tometer at the moment of closing the stopcock of the density bulb. 



The details of the experiment are these : 



