AND RATIO OF THKIR ATOHtTC AVKIOHTS. 51 



OBSERVATIONS WITH GLOUE 3. 



Weijjlit of Density of 



Number. oxygen: oxygen; 



gramnies. grammes. 



I 27.7546 1.42880 



2 27-7.S,?S '.42874 



3 27.7542 1.42878 



4 -'7-753° 1. 42^^72 



5 27-75°7 1-42859 



6 27.7490 1.42851 



If we increase the mean by one tliirty-thoiisaiultli,* we get 



1) = 1.42887 gr. ± 0.000048. 



.■{3. OXYGEN HY TIIIKD MKTIIol). 



In a third series of detei'niinations of the density of oxygen, tlie globes were 

 sui'rounded witli melting ice while tilling Avith the gas, and the pressure was 

 measured by connectiug the globe to tlie syphon barometer. The surface of the 

 globe was therefore exposed to contact with water ; as it Avas convenient to put the 

 globe in position in the ice before the operation of exhausting the connecting tubes 

 and filling it with oxygen, the contact was somewhat pi'olonged. Change of weight 

 of the globes during the exposure was therefore inevitable; it was accordingly 

 thought proper to determine the weight of the glol)e filled with oxygen, and then 

 to exhaust it and determine its weight when empty, and to consider the difference 

 of the two weighings as expressing the weight of the gas remove<l by the 

 exhaustion. An attempt was made to piotect the stopcocks and their lubrication 

 from the action of water by surrounding them with rubber capsules while they lay 



in the ice. 



The cistern of the Ijni'ometer was at the level of the centre of the globes dur- 

 ing this series of determinations. Tlie reduction of the observations took account 

 of the force of gi-avity at my lab.)iMt(n'y, and of tlie correction to the length of the 

 scale of my bai'ometer. 



34. OXYGEN BY THIK1> .METHOD. FILLlN(i THE GLOBES Wn'H OXYGEN. 



The globe a, Fig. 22, was placed in a cylinder, /, and suiTOunded with finely 

 crushed ice. This cylinder stood in a lai-ge tank, h, also filled with ice, so that the 

 globe was surrounded on all sides \vith a layer of more than thii'ty centimetres of 

 ice. To the joint c was fitted the tube which led to a self-acting Toepler pump, to 

 the apparatus for pi'oducing oxygen, and to the syphon barometei-. The globe and 



* See note, page 28. 



