AND RATIO OF THEIR ATOMIC WKKill'l'S. 61 



the result of m;iiiy pi'evioiis e.xaiiiiii.-itioiis luid shown li<>\v to ol>t;iiii the gas witli 

 no measurable amount ot" impurity. 



It may be not without interest to consider how small an amount of nitrogen 

 might be detected when mixed with hydrogen. If the hydrogen should be 

 removed from the mixture by absorption, as carbon dioxide may be i-emoved, it 

 would be possible to detect a very small quantity. My measuring apparatus, foi- 

 instance, would measure a considei'ably smaller quantity than the thousandth of a 

 cubic centimetre. If, then, two litres of hydi'ogen were absorbed by some suppos- 

 able reagent for the pui-pose, a two-millionth of nitrogen would ])e detected. But 

 the case is dift'ei'ent when the amount of hydrogen in a mixture must be determined 

 by explosion with oxygen. In my experiments, two litres of hydrogen were 

 reduced to ten cubic centimetres l)y absorption by means of copper oxide, but the 

 remaining ten centimetres had to be measured, and the hydrogen determined by 

 explosion, and the nitrogen determined by difference. With sufficient care, one 

 ought to be able to answer for a hundredth of a cubic centimetre; for how much 

 less, I have no means of knowing. 



But to detect a huudredtli of a cubic centimetre, in the case supposed (and 

 i-ealized), means to detect a two-hundred-thousandth ; to this approximation, the 

 examination was carried, in duplicate analyses, with the result that hydrogen con- 

 taininir less than this could be obtained in the usual working of the apparatus, 

 except after fracture. The removal of nitrogen fi-oni the apparatus was then 

 tedious, but the result was certain, and hydrogen of su.-h purity is thought to have 

 been used in all the experiments of this series. 



7. SECOND METHOD. I'HKr'AKATION OK HYDROfiEN. 



Hydrogen was prepared in this series of experiments in very nearly the same 

 way as in the preceding; but some details were different. The hydrogen from 

 the voltameter passed through an almost saturated solution of potassium hydroxide, 

 over incandescent copper, through a tube one metre long and two and a half centunetres 

 in diameter, which was filled with glass beads moistened with a strong solution of 

 lead oxide in potassium hydroxide, then through three tubes of the same dimen- 

 sions, filled with calcium chloride, with powdered potassium hydroxide, and with 

 phosphorus pentoxide. Here was placed a manometer and a regulating stopcock ; 

 all parts were connected by fusion, except where infusible glass had to be con- 

 nected to the soft glass of the rest of the apparatus. 



When the tube containing palladium was to be filled, it was connected by 

 fusion to the tube delivering pure hydrogen, and was heated. When it was so hot 



