A NEW CONSTITUENT OF THE ATMOSPHERE. 205 
hung from the end of the beam to which it was suspended, and the final weight was 
adjusted by means of a rider, 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 with gloves, to avoid moisture or grease from the fingers. 
Three experiments, 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 result gave for the weight of one litre of air 
at 0° and 760 millims. pressure, 1°2935 grm. REGNAULT found 1:29340, a correction 
having been applied by Crafts to allow for the estimated alteration of volume caused 
by the contraction of his vacuous bulb. The mean result of determinations by several 
observers is 1°29347 ; while one of us found 1°29327. 
The globe was then filled with the carefully dried gas. 
Temperature, 18°80°. Pressure, 759°3 millims. 
Weight of 162°843 cub. centims. of gas 2. |. . . «021897 grm. 
Weight of 1 litre gas at O° and 760 millims. . . . . 1°4386_,, 
Density, that of air compared with O,=16, being 14'476 16°100  grms. 
It is evident from these numbers that the dense constituent of the air was being 
concentrated. As a check, the bulb was pumped empty and again weighed ; its 
weight was 0'21903 srm. This makes the density 16°105. 
It appeared advisable to continue to absorb nitrogen from this gas. The first tube 
of magnesium removed a considerable quantity of gas; the nitride was converted 
into ammonium chloride, and the sample contained 66°30 per cent. of chlorine, 
showing, as has before been remarked, that if any of the heavier constituent of the 
atmosphere had been absorbed, it formed no basic compound with hydrogen. The 
second tube of magnesium was hardly attacked; most of the magnesium had melted, 
and formed a layer at the lower part of the tube. That which was still left in the 
body of the tube was black on the surface, but had evidently not been much attacked. 
The ammonium chloride which it yielded weighed only 0:0035 grm. 
The density of the remaining gas was then determined. But as its volume was 
only a little over 100 cub. centims., the bulb, the capacity of which was 162 cub. 
centims., 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 noting the 
level of the mercury in the gas-holder and in the tube which served as a mercury 
reservoir against a graduated mirror-scale by help of a cathetomer at the moment of 
closing the stop-cock of the density bulb. 
The details of the experiment are these :— 
Temperature, 19°12°C. Barometric pressure, 749°8 millims. (corr.). 
Difference read on gas-holder and tube, 225°25 millims. (corr.). 
Actual pressure, 524°55 millims. 
