570 



NATURE 



[April 13, 1893 



did the copper in the furnace, even at the end where the gas 

 entered, show any sign of losing its metallic appearance. 

 Three results, obtained in August, 1892, were : — 



August 8 231035 



,, 10 2-31026 



,, 15 2-31024 



Mean 2-31028 



To these may be added the results of two special experiments 

 made to test the removal of hydrogen by the copper oxide. For 

 t'his purpose a small hydrogen generator, which could be set in 

 action by closing an external contact, was included between the 

 two tubes of reduced copper, the gas being caused to bubble 

 through the electrolytic liquid. The quantity of hydrogen 

 liberated was calculated from the deflection of a galvanometer 

 included in the circuit, and was sufficient, if retained, to alter 

 the density very materially. Care was taken that the small 

 stream of hydrogen should be uniform during the whole time 

 (about 2\ hours) occupied by the filling, but, as will be seen, 

 the impurity was effectually removed by the copper oxide. ^ 

 Two experiments gave — 



September 17 2-31012 



„ 20 2-31027 



Mean 2-31020 



We may take as the number for nitrogen — 



2-31026 

 Correction for contraction ... 56 



2-31082 



Although the subject is not yet ripe for discussion, I cannot 

 omit to notice here that nitrogen prepared from ammonia, and 

 expected to be pure, turned out to be decidedly lighter than the 

 above. When the oxygen of air is burned by excess of am- 

 monia, the deficiency is about i/ioooth part.- When oxygen is 

 substituted for air, so that all (instead of aTjout one-seventh 

 part) of the nitrogen is derived from ammonia, the deficiency of 

 weight may amount to I percent. It seems certain that the 

 abnormal lightness cannot be explained by contamination with 

 hydrogen, or with ammonia, or with water, and everything 

 suggests that the explanation is to be sought in a dissociated 

 state of the nitrogen itself. Until the questions arising out of 

 these observations are thoroughly cleared up, the above number 

 for nitrogen must be received with a certain reserve. But it 

 has not been thought necessary, on this account, to delay the 

 presentation of the present paper, more especially as the method 

 employed in preparing the nitrogen for which the results are 

 recorded is that used by previous experimenters. 



Reduction to Standard Pressure. 



The pressure to which the numbers so far given relate is that 

 due to 762-511 mm. of mercury at a temperature of 14° 85,^ 

 and under the gravity operative in my laboratory in latitude 

 51° 47'. In order to compare the results with those of other 

 experimenters, it will be convenient to reduce them not only to 

 760 mm. of mercury pressure at 0°, but also to the value of 

 gravity at Paris. 



The product of the three factors, corrective for length, fof 

 temperature, and for gravity, is 0-99914. ihus multiplied, the 

 numbers are as follows : — 



Air. Oxygen. Nitrogen. 



2-37512 2-62534 2-30883 



and these may now be compared with the water contents of the 

 globe, viz. 1836-52. 



The densities of the various gases under standard conditions, 

 referred to that of distilled water at 4°, are thus : — 



Air. Oxygen. Nitrogen. 



0-00129327 0-00142952 O-OOI25718 



With regard to hydrogen, we may calculate its density by 



' Much larger quantities of hydrogen, sufficient to reduce the oxide over 

 several centimetres, have been introduced without appreciably altering the 

 weight of the gas. 

 ■ '- Nature, vol. xlvi. p. 512. 



■* The thermometer employed with thi manometer read o' '15 too high. 



J^O- I?24, VOL. 47] 



means of the ratio of densities of oxygen and hjrdrogen formerly 

 given by me, viz. 15-882. Hence 



Hydrogen. 



o 000090009. 

 The following table shows the results arrived at by various 

 experimenters. Von Jolly did not examine hydrogen. The 

 numbers are multiplied by 1000 so as to exhibit the weights in 

 grams per litre : — 



Air. Oxygen. Nitrogen. Hydrogen. 



Regnault, 1847 1-29319 ... i -42980 .. 1-25617 ... 0-089^8 



Corrected by Crafts.. I -29349 ... 1-43011 ... 1-25647 ... 008988 



Von Jolly, 1880 1 -29351 ... 1-42939 ... 1-25787 — 



Ditto corrected 1-29383 ... 1-42971 ... 1-25819 — 



Leduc, 1891I 1-29330 ... 1-42910 ... 1-25709 ... 0-08985 



Rayleigh, 1893 1-29327... 1-42952... 1-25718 ... 0-09001 



The correction of Regnault by Crafts (Comptes Rendus, vol. 

 cvi., p. 1664) represents allowance for the contraction of Reg- 

 nault's globe when exhausted, but the data were not obtained 

 from the identical globe used by Regnault. In the fourth row I 

 have introduced a similar correction to the results of von Jolly. 

 This is merely an estimate founded upon the probability that the 

 proportional contraction would be auout the same as in my own 

 case and in that of M. Leduc. 



Ir^ taking a mean we may omit the uncorrected numbers, 

 and also ttiat obtained by Regnault for nitrogen, as there is 

 reason to suppose that his gas was contaminated with hydrogen. 

 Thus 



Mean Numbers. 

 Air. Oxygen. Nitrogen. Hydroa;en. 



1-29347 1-42961 i'25749 0-08991 



The evaluation of the densities as compared with water is ex- 

 posed to many sources of error which do not affect the com- 

 parison of one gas with another. It may, therefore, be instructive 

 to exhibit the results of various workers referred to air as 

 unity. 



Oxygen. Nitrogen. Hydrogen. 



Regnault (corrected) 1-10562 ... o'97£38 ... 006949 

 V. Jolly (corrected) 1-10502 ... 0-97245 ... — 



Leduc 1-1050 ... 0-9723 ... 006947 



Rayleigh 1-10535 ... 0-97209 ... 006960 



Mean 1-10525 ... 0-97218 ... 0-06952 



As usually happens in such cases, the concordance of the 

 numbers obtained by various experimenters is not so good as 

 might be expected from the work of each taken separately. The 

 most serious discrepancy is in the difficult case of hydrogen. 

 M. Leduc suggests {Comptes Rendus, July, 1892) that my num- 

 ber is too high on account ot penetration of air through the blow- 

 off tube (used to establish equilibrium of pressure with the 

 atmosphere), which he reckons at I m. long and i cm. in 

 diameter. In reality the length was about double, and the 

 diameter one-half of these estimates ; and the explanation is 

 difficult to maintain, in view of the fact, recorded in my paper, 

 that a prolongation of the time of contact from 4'" to 30'" had 

 no appreciable ill effect. It must be admitted, however, that 

 there is a certain presumption in favour of a lower number, 

 unless it can be explained as due to an insufficient estimate for 

 the correction for contraction. On account of the doubt 

 as to the appropriate value of this correction, no great 

 weight can be assigned to Regnault 's number for hydrogen. If 

 the atomic weight of oxygen be indeed 15-88, and the ratio of 

 densities of oxygen and hydrogen be 15 90, as M. Leduo makes 

 them, we should have to accept a much higher number for the 

 ratio of volumes than that (2-0002) resuhing from the very 

 elaborate measurements of Morley. But while I write the in- 

 formation reaches me that Mr. A. Scott's recent work upon the 

 volume ratio leads him to just such a higher ratio, viz. 2-00245, 

 a number a priori more probable than 2-0002. Under the cir- 

 cumstances both the volume ratio and the density of hydrogen 

 must be regarded as still uncertain to the i/ioooth part. 



ELECTRICAL RAILWAYS} 

 r^NE of the most striking of the many new departures in the 

 ^^ practical application of electrical science, which made the 

 Paris Exhibition of 1881 memorable, was a short tramway laid 



1 Bulletin des Seances de la Socle tc de Physique. 



■-' Kiiday evening discourse delivered at the rCoyi^N Institution by Dr. 

 Edward Hopkinson on February 24. 



