208 



NA TURE 



[December 30, 1897 



gases are either imprisoned or are free to escape. For the earth, 

 under favourable circumstances, a velocity of lo*5 km. per sec. 

 would be sufficient to carry a molecule beyond gravitational 

 control, and this is 6'5 times the " velocity of mean square" in 

 hydrogen gas at a temperature of - 66° C. ; 9*27 times that of 

 helium at the same temperature, and I9"66 times that of water 

 vapour. Since the two former gases escape and the latter does 

 not, it would seem that the velocity attained by molecules can 

 exceed nine times the average velocity, but cannot reach that of 

 twenty. Assuming that Venus retains a moisture-laden atmo- 

 sphere, about which Dr. Stoney seems very positive, this latter 

 number can be reduced to eighteen, and thus still closer express 

 the actual velocity in terms of that of the " mean square." 



Limiting the inquiry to a temperature of - 66° C, Dr. Stoney 

 applies the theory to all members of the solar system with the 

 following results. From the moon all gases having a vapour 

 density less than 39 will escape with greater promptness than 

 helium does from the earth. On Mercury, water cannot exist, 

 while nitrogen and oxygen would gradually dribble away. The 

 conditions on Venus resemble those on the earth, but the case 

 of Mars is of exceptional interest. Dr. Stoney says that it is 

 legitimate to infer that on this planet water cannot remain. 

 The atmosphere he considers to consist mainly of nitrogen, 

 argon, and carbon dioxide. He thinks there is no vegetation, as 

 we understand the term, on the surface of the planet, and the 

 snow, frost, and fog do not arise from the same 'cause as on the 

 earth. Jupiter is able to imprison all gases known to chemists, 

 but whether the more distant members of our system can retain 

 hydrogen is doubtful. Helium and the denser gases probably 

 float in their atmospheres, but the molecules of the lighter gases 

 are describing orbits about the sun, the velocity they cap acquire 

 enabling them to escape from planetary control, but still 

 insufficient to liberate them from the gravitational influence of 

 the sun. 



THE DENSITIES OF CERTAIN GASES} 



"T^HE observations here recorded were carried out by the 

 ■*• method and with the apparatus described in a former 

 paper,- to which reference may be made for details. It must 

 suffice to say that the globe containing the gas to be weighed 

 was filled at 0° C, and to a pressure determined by a mano- 

 metric gauge. This pressure, nearly atmospheric, is slightly 

 variable with temperature on account of the expansion of the 

 mercury and iron involved. The actually observed weights are 

 corrected so as to correspond with a temperature of 15'^ C. of 

 the gauge, as well as for the errors in the platinum and brass 

 weights employed. In the present, as well as in the former, 

 experiments I have been ably a.ssisted by Mr. George Gordon. 



Carbonic Oxide. 



This gas was prepared by three methods. In the first method 

 a flask, sealed to the rest of the apparatus, was charged with 80 

 grams recrystallised ferrocyanide of potassium and 360 c.c. 

 strong sulphuric acid. The generation of gas could be started 

 by the application of heat, and with care it could be checked 

 and finally stopped by the removal of the flame with subsequent 

 application, if necessary, of wet cotton wool to the exterior of 

 the flask. In this way one charge could be utilised with great 

 advantage for several fillings. On leaving the flask the gas was 

 passed through a bubble containing potash solution (convenient 

 as allowing the rate of production to be more easily estimated), 

 and thence through tubes charged with fragments of potash and 

 phosphoric anhydride, all connected by sealing. When possible, 

 the weight of the globe///// was compared with the mean of the 

 preceding and following weights empty. Four experiments 

 were made with results agreeing to within a few tenths of a 

 milligram. 



In the second set of experiments the flask was charged with 

 100 grams of oxalic acid and 500 c.c. strong sulphuric acid. To 

 absorb the large quantity of COo simultaneously evolved a 

 plentiful supply of alkali was required. A wash-bottle and a 

 long nearly horizontal tube contained strong alkaline solution, 

 and these were followed by the tubes containing solid potash 

 and phosphoric anhydride as before. 



1 "On the Densities of Carbonic Oxide, Carbonic Anhydride, and 

 Nitrous Oxide." By Lord Rayleigh, F.R.S. (Read at the Royal Society, 

 December 9, 1897.) 



2 "On the Densities of the Principal Gases," Roy. Soc. Proc, vol. liii. 

 p. 134, 1893. 



NO. 1470, VOL. 57] 



For the experiments of the third set oxalic acid was replaced 

 hy formic, which is more convenient as not entailing the absorp- 

 tion of large volumes of COg. In this case the charge consisted 

 of 50 grams formate of soda, 300 c.c. strong sulphuric acid, and 

 150 c.c. distilled water. The water is necessary in order to 

 prevent action in the cold, and the amount requires to be some- 

 what carefully adjusted. As purifiers, the long horizontal 

 bubbler was retained and the tubes charged with solid potash 

 and phosphoric anhydride. In this set there were four con- 

 cordant experiments. The immediate results stand thus : — 



Carbonic Oxide. 



From ferrocyanide 

 ,, oxalic acid ... 

 ,, formate of soda 



Mean... 



2 '29843 

 2*29852 

 2-29854 



2-29850 



This corresponds to the number 2*62704 for oxygen {loc. cii., 

 p. 144), and is subject to a correction (additive) of 000056 for 

 the diminution of the external volume of the globe when 

 exhausted. 



The ratio of the densities of carbonic oxide and oxygen is 

 thus 2*29906 : 2-62760 ; so that if the density of oxygen be taken 

 as 32, that of carbonic oxide will be 27*9989. If, as some pre- 

 liminary experiments by Dr. Scott {Camb. Phil. Proc, vol. ix. 

 p. 144, 1896) indicate, equal volumes may be taken as accurately 

 representative of CO and of Oo, the atomic weight of carbon will 

 be 1 1 -9989 on the scale of oxygen = 16. 



The very close agreement between the weights of carbonic 

 oxide prepared in three different ways is some guarantee against 

 the presence of an impurity of widely differing density. On the 

 other hand, some careful experiments led Mr. T. W. Richards 

 {Amer. Acad. Proc , vol. xviii. p. 279, 1891) to the conclusion 

 that carbonic oxide is liable to contain considerable quantities of 

 hydrogen or of hydrocarbons. From 5^ litres of carbonic oxide 

 passed over liot cupric oxide he collected no less than 25 milli- 

 grams of water, and the evidence appeared to prove that the 

 hydrogen was really derived from the carbonic oxide. Such a 

 proportion of hydrogen would entail a deficiency in the weight 

 of the globe of about li milligrams, and seems improbable in 

 view of the good agreement of the numbers recorded. The 

 presence of so much hydrogen in carbonic oxide is also difficult 

 to reconcile with the well-known experiments of Prof Dixon, 

 who found that prolonged treatment with phosphoric anhydride 

 was required in order to render the mixture of carbonic oxide and 

 oxygen inexplosive. In the presence of relatively large quantities 

 of free hydrogen (or hydrocarbons) why should traces of water 

 vapour be so important ? 



In an experiment by Dr. Scott (C/iem. Soc. Trans., 1897, p. 

 564), 4 litres of carbon monoxide gave only i '3 milligrams to the 

 drying tube after oxidation. 



I have myself made several trials of the same sort with gas 

 prepared from formate of soda exactly as for weighing. The 

 results were not so concordant as I had hoped, ^ but the amount 

 of water collected was even less than that given by Dr. Scott. 

 Indeed, I do not regard as proved the presence of hydrogen at 

 all in the gas that I have employed.^ 



Carbonic Anhydride. 



This gas was prepared from hydrochloric acid and marble, and 

 after passing a bubbler charged with a solution of carbonate of 

 soda, was dried by phosphoric anhydride. Previous to use, the 

 acid was caused to boil for some time by the passage of hydro- 

 chloric acid vapour from a flask containing another charge of the 

 acid. In a second set of experiments the marble was replaced by 

 a solution of carbonate of soda. There is no appreciable 

 difference between the results obtained in the two ways ; and the 

 mean, corrected for the errors of weights and for the shrinkage 

 of the globe when exhausted, is 3-6349, corresponding to 2-6276 

 for oxygen. The temperature at which the globe was charged 

 was o" C, and the actual pressure that of the manometric gauge 

 at about 20°, reduction being made to 15° by the use of Boyle's 

 law. From the former paper it appears that the actual height of 

 the mercury column at 15° is 762*511 mm. 



1 One obstacle was the difficulty of re-oxidising the copper reduced by 

 carbonic oxide. I have never encountered this difficulty after reduction by 

 hydrogen. . 



2 In Mr. Richards' work the gas in an imperfectly dried condition was 

 treated with ho t platinum black. Is it possible that the hydrogen was intro- 

 duced at this stage ? J 



