322 



NATURE 



[_Aug\ 19, 187- 



p,-,. „ „ Vol. CO, at 0° & Vol. CO2 at 6" 62 

 Pressure, ^^o millims. = i. and 31-06 at. = i 

 at. 



31-06 0-02589 i-oooo 



31-06 0-03600 1*3905 



31-06 



and Vol. C0„ at. 6' 

 I. and 40 "06 at. = 



Temperature. 



,-62, 

 63-83 



p„„,„. Vol. CO^at 

 Pressure, yg^ „iilims 



0-02589 

 0-03600 

 0-04160 i-6o68 100-64) 



Temperature. 



(B) 



6 01 

 63-64 

 100 60 



(C) 



40-06 0-01744 i-oooo 



40-06 002697 1*5464 



40-06 003161 I -8123 



Taking as unit I vol. of carbonic acid at 6°-o5 and 22-26 

 atmospheres, we obtain from series A the following values for 

 the coefficient of heat for different ranges of temperature : — 

 a = 0-005499 from 6°' 05 to 63°- 79 

 a = 0-005081 from 63°-79 to I0D°-I 

 From series B, with the corresponding unit volume at 6°- 6a 

 and 31°- 06 atmospheres, we find : — 



a =- 0-006826 from 6°-62 to 63°- 83 

 a = 0-005876 from 630-83 to ioo°-64 

 And in like manner from series C with the unit volume at 

 6°-oi and 40- 06 atmospheres : — 



a = 0-009481 from 6°-oi to 63^-64 

 o = 0-007194 from 63°-64 to ioo°-6o 



The co-efficient of carbonic acid under one atmosphere referred 

 to a unit volume at 6° is 



a = 0-003629 



From these experiments it appears that the co-efficient of ex- 

 pansion increases rapidly with the pressure. Between the tem- 

 peratures of 6° and 64° it is once and a half as great under 22 

 atmospheres, and more than two and a half times as great under 

 40 atmospheres, as at the pressure of i atmosphere. Still more 

 important is the change in the value of the co-efficient at different 

 parts of the thermometric scale, the pressure remaining the same. 

 An inspection of the figures will also show that this change of 

 value at different temperatures increases with the pressure. 



Another interesting question, and one of great importance in 

 reference to the laws of molecular action, is the relation between 

 the elastic forces of a gas at different temperatures while the 

 volume remains constant. The experiments which I have made 

 in this part of the inquiry are only preliminary, and were per- 

 formed not with pure carbonic acid, but with a mixture of about 

 II volumes of carbonic acid and i volume of air. It will be 

 convenient, for the sake of comparison, to calculate, as is usually 

 done, the values of a from these experiments ; but it must be 

 remembered that o here represents no longer a coefficient of 

 volume, but a coefficient of elastic force. 



Elastic force of a mixture of ii vol. COg and i vol. air heated 

 under a constant volume to different temperatures. 

 Vol. CO4. Temperature. Elastic Force. 



(A) 



(B) 



From series A we deduce for a unit at 13° -70 and 22° -90 

 atmospheres : — 



a = 0-004604 from 13° -70 to 40* -63 

 a = 0-004367 from 40° -63 to 99° "73 

 And from series B : — 



a = o 005067 from 13° 70 to 40° -66 

 a = 0-004804 from 40° -66 to 99° -75 

 The coefficient at 13° -70 and i atmosphere is 

 a = 0-003513 



It is clear that the changes in the values of ^, calculated from 

 the elastic forces under a constant volume, are in the same direc- 

 tion as those already deduced from the expansion of the gas 

 under a constant pressure. The value of a increases with the 

 pressure, and it is greater at lower than at higher temperatures. 

 But a remarkable relation exists between the coefficients in the 

 present case which does not exist between the coefficients ob- 

 tained from the expansion of the gas. The values of a, deduced 

 for the same range of temperature from the elastic forces at 



different pressures, are directly proportional to one another. \ , 

 have, in short— 



?:2?4367^ 0-9485, ?:^°4^ 0-9481. 



0.004604 0-05067 



How far this relation will be found to exist under other condi- 

 tions of temperature and pressure will appear when experiments 

 now in progress are brought to a coticlusion. 



Laxv of Dalton. — This law, as originally enunciated by its 

 author, is, that the particles of one gas possess no repulsive or 

 attractive power with regard to the particles of another. " Oxy- 

 gen gas," he states, "azotic gas, hydrogenous gas, carbonic acid 

 gas, aqueous vapour, and probably several other elastic fluids 

 may exist in company under any pressure and at any temperature 

 without any regard to their specific gravities, and v/ithout any 

 pressure upon one another." The experiments which I have 

 made on mixtures of carbonic acid and nitrogen have occupied a 

 larger portion of time than all I have yet referred to. They 

 have been carried to the great pressure of 283 -9 atmospheres, as 

 measured in glass tubes by a hydrogen manometer, at which 

 pressure a mixture of three volumes carbonic acid and four 

 volumes nitrogen was reduced at 7° -6 to ^fs of its volume with- 

 out liquefaction of the carbonic acid. As this note has already 

 extended to an unusual length, I will not now attempt to give 

 an analysis of these experiments, but shall briefly state their 

 general results. The most important of these resiilts is the lower- 

 ing of the critical point by admixture with a non-condeitsable gas. 

 Thus in the mixture mentioned above of carbonic acid and 

 nitrogen, no liquid was formed at any pressure till the tempera- 

 ture was reduced below — 20° C. Even the addition of only ^^ 

 of its volume of air or nitrogen to carbonic acid gas will lower 

 the critical point several degrees. Finally, these experiments 

 leave no doubt that the law of Dalton entirely fails under high 

 pressures, where one of the gases is at a temperature not greatly 

 above its critical point. The anomalies observed in the tension 

 of the vapour of water, when alone and when mixed with air, 

 find their real explanation in the fact that the law of Dalton is 

 only approximately true in the case of mixtures of air and 

 aqueous vapour at the ordinary pressure and temperature of the 

 atmosphere, and do not depend, as has been alleged, on any dis- 

 turbing influence produced by a hygroscopic action of the sides 

 of the containing vessel. The law of Dalton, in short, like the 

 laws of Boyle and Gay-Lussac, only holds good in the case of 

 gaseous bodies which are at feeble pressures and at temperatures 

 greatly above their critical points. Under other conditions 

 these laws are interfered with ; and in certain conditions (such 

 as some of those described in this note) the interfering causes 

 become so powerful as practically to efface them. 



SCIENTIFIC SERIALS 



Foggendorff'' s Annalen der Fhysik U7td Chetnie, Nos. 5 and 6. 

 — These parts contain the following papers : — No. 5 : On the 

 variations in the phases of light when reflected from glass, by 

 P. Glan ; account of experiments made in the physical labora- 

 tory of Berlin University, under the direction of Prof. Ilelmholtz. 

 — On some remarkable growths of quartz crystals on calcareous 

 spar from Schneeberg in Saxony, by Aug. Frenzel of Freiberg, 

 and G. vom Rath of Bonn. — Mineralogical researches, by G. 

 vom Rath. This paper treats of pseudomorphous monticellite 

 from Pesmeda, on the Monzoni Mountain in Tyrol, of rhombic 

 sulphur, of calcareous spar from Ahren (Tyrol), and of a peculiar 

 specimen of quartz from Japan. — On a method to determine 

 extra currents electroscopically, by Dr. F. Fuchs. — On the 

 electric conduction resistance of air, by A. Oberbeck. — On the 

 absorption and refraction of light in metallic opaque bodies, by 

 W. Werniche. — On the changes which take place in temperature 

 at the passage of an electric current from one metal to another, 

 by Dr. Heinr. Buff, — On the isodynamical planes round a ver- 

 tical magnetic rod, and their application in an investigation of 

 iron ore deposits, based upon magnetic measurements, by Rob. 

 Thalen. — A paper on the same subject, by Th. Dang. Both 

 these papers are from the Kongl. Vetenskaps Forhandlingar. — 

 Spectroscopic Notes, by J, Norman Lockyer : On the evidence 

 of variation in molecular structure, and On the molecular struc- 

 ture of vapours in connection with their densities. These Notes 

 are translated from the Proceedings of the Royal Society, 

 June II, 1874. — On the distribution of heat in the normal spec- 

 trum, by G. Lundquist. — On the time of attraction and repulsion 

 of electro-magnets, by Dr. Schneebeli.— On the mathematical 



