18i>3.] On the Densities of the Principal Gases. 143 



" empty," except in the case of October 15, when there was no sub- 

 sequent weighing empty. The results are 



September 27 2-37686 



29 2-37651 



October 3 2'37653 



8 '2-37646 



11 237668 



13 2-37679 



15 2-37647 



Mean 2-37661 



There is here no evidence of the variation in the density of air sus- 

 pected by Regnault and v. Jolly. Even if we include the result for 

 September 27th, obviously affected by irregularity in the weights of 

 the globe empty, the extreme difference is only 04 milligram, or about 

 l/6000th part. 



To allow for the contraction of the globe (No. 14) when weighed 

 empty, discussed in my former papers, we are to add 0*00056 to the 

 apparent weight, so that the result for air becomes 



2-37717. 



This is the weight of the contents at 0° and under the pressure 

 defined by the manometer gauge at 15° of the thermometer. The 

 reduction to standard conditions is, for the present, postponed. 



Oxygen. 



This gas has been prepared by three distinct methods : (a) from 

 chlorates, (6) from permanganate of potash, (c) by electrolysis. 



In the first method mixed chlorates of potash and soda were 

 employed, as recommended by Shenstone. the advantage lying in the 

 readier fusibility. The fused mass was contained in a Florence flask, 

 and during the wash-out was allowed slowly to liberate gas into a 

 vacuum. After all air had been expelled, the regulating tap was 

 closed, and the pressure allowed gradually to rise to that of the 

 atmosphere. The temperature could then be pushed without fear of 

 distorting the glass, and the gas was drawn off through the regulating 

 tap. A very close watch over the temperature was necessary to 

 prevent the evolution of gas from becoming too rapid. In case of 

 excess, the superfluous gas was caused to blow off into the atmo- 

 sphere, rather than risk imperfect action of the potash and phosphoric 

 anhydride. Two sets of five fillings were effected with this oxygen. 

 In the first set (May, 1892) the highest result was 2-6272, and the 



