•2'2 DENSITIES OF OXYOEN AND HYDROGEN 



u.\yi,'cii aiul iiitn»sien iliHVr bill h\ an eigbtli part, even tlie niaxinnini found was 

 negligible in its effect on tlie density of oxygen. 



In some experiments, almiit half of the oxygen mntained in a globe was eom- 

 liined with liydrogen, and chlorine sought in the water thus produced. Sometiinc-; 

 it could not l)e detected ; it never aniounteil to the twentieth of a milligramnic. it 

 was in the same exi)eriments that the presence of nitrogen was investigated; after 

 twenty litres of oxygen had been combined with liydidgen, the residue was analyzed, 

 and the amount of nitrogen measured, with the result given above. 



If the aljsorj)tion of chlorine was so com})lete, it may be hoped that the ab- 

 soiptiou of carbon dioxide was also complete. The experiments to detect chlorine 

 also served to detect carbon dioxide, and the amount found was uesrlii'ible. 



Whether any va^ior of mercury interfered with the trustworthiness of the 

 determinations cannot be affirmed ; the evidence is too indirect, lint the evidence 

 is perhaps sufficient that the error, if any, is negligible. If the density of oxygen 

 is in error for this cause, the error in the determination of the density of hydrogen 

 by the same method, in the same conditions, would be some sixteen times as much. 

 But I have succeeded in determining the density of hydrogen, not only in exactly 

 the way used for oxygen, but also in a way in which the error from the presence 

 of vapor of mercury is entirely avoided ; and this eri'or is found to be not above 

 some such (piantity as one thousandth of the density of hydrogen ; therefore in 

 the case of oxygen it is not likely to lie more than the ten or twenty-thousandth 

 part. 



1*1. — JIEASLKEJIENTS OF TEMPERATURE AND PRESSURE. 



The temperature of the gas in the glol)e <t Fig. •>, while resting in the case 

 /// ifi, was observed Ity means of two thermometers made of .Icna normal glass anil 

 divided into fiftieths. Their bulbs were diametrically opposite, one near the top 

 and the other near the bottom of the irlobe. 



The pressure of the g;is in <i, was measured with the, mano-bai-ometer shown in 

 Fig. 8. The tubes a and /> together constitute a syphon barometer; c is tlie tube 

 which was used to measure the pressuie of the oxygen in this set of experiments; 

 a fourth being used for the experiments on livdiOLreii which were made at the same 

 time. The tubes all stood in a box containins: water, two of the faces of which 

 were made of selected plate glass. In front of each tube and in contact with it was 

 a glass scale graduated into millimetres. The lines of the scale are about three 

 thousandths of a millimetre in width, so that the uncertainty in setting a division 

 of the eyepiece micnjineter for coincidence is negligible. The three scales were of 

 the same kin<l of glass, graduated at the same time, and agreed well with e.-ich other. 

 They were adjusted so that their three zeros were on the same level, as shown by 



