PAKT II. ON TIIK DENSITY OF HYDROGEN. 



1. 1NTI;<>I)I"(TT(>X. 



Tlie density of liyiliogcii lias bccii iletermiued in tive series of experiments of 

 very uneqiiiil value. In the first series, temperature and [)ressure were measureil 

 with mercurial thermometers and tlie mano-barometer. Tlie reduction took account 

 of the same factors as the reduction of the first series in tht- case of oxygen. This 

 series consisted of fifteen separate determinations. 



In a second series, the globes were surrt>undt'(l with melting ice while the 

 pressure was measured with the syphon barometer. The icduction was the same 

 as in tlie third series of e.xpeiimeiits on oxygen. Tiiis series consisted of nineteen 

 experiments. 



in a tliiid series the hydrogen was wciglicd, iini in the globes where its volume 

 temperature, and pressure were observed, but befoi'e it was inlrnduced into them. 

 Globes making jointly a capacity of forty-two litres were connected togethei-, 

 and to a self-acting air pump, to a syphon barometer, and to a tube for admitting 

 hydrogen. A tube containing six hundred grammes of })alladium foil was charged 

 \vith hydrogen, and was weighed.. Its iiydri>gen was transfeired to the gloVjes, pre- 

 viously exhausted and shut ott" from the air-puni]). Here its volume and [>ressuie 

 were determined at the temperature of melting ice. The tube of palladium was again 

 weighed, and so the weigiit of hydrogen was determined. This series consisted of 

 eight experiments, togethei' with five expeiiments w Inch were made before the 

 apparatus and its manipulation were satisfactory, and which wei'e regarded as only 

 preliminary. The leduction of these observations takes account of the elevation of 

 the cistern of the barometer al)ove the centre of the globes and of the force of 

 gravity at my laboratory. 



'{'he fourth series was simpl)' a continuation of the third aftei' a summer vaca- 

 tion. Seveial accidents occurretl. The series was therefore abandoned, and a new 

 .•ippaiatus was constructed. The fifth series was a repetition of the third and fourth 

 with a different apparatus; these two series consisted of six and eleven experiments 



respectively, l)ut accidents occurred in two ex[)erinu'nts of the fouitli series. 



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