LORD l:APT,ElGIT: ON THE OXIDATI@X OF NITROGEN GAS. 181 By LORD RAYLEIGH. THE observations here described were made in connection with the isolation of argon by removal of the nitrogen from air, but they may, perhaps, possess a wider interest as throwing light upon the behaviour of nitrogen itself. According to Davy,* the dissolved nitrogen of water is oxidised to nitrous (or nitric) acid when the liquid is submitted to electrolysis. “TO make the experiment in as refined a form as possible, I procured two hollow cones of pure gold containing about 25 grains of water each, they were filled with distilled water connected together by a moistened piece of amianthus which had been used in the former experiments, and exposed t o the action of a voltaic battery of 100 pairs. , .. I n 10 minutes the water in the negative tube had gained the power of giving a slight blue tint to litmus paper : and the water in the positive tube rendered i t red. The process was continued for 14 hours ; the acid increased in quantity during the whole time, and the water became a t last very sour t.0 the taste. . . . The acid, as f a r as its properties were examined, agreed with pure nitrous acid having an excess of nitrous gas ” (p. 6). Further (p. lo), ‘‘ 1 had never made any experiments, in which acid matter having the properties of nitrous acid was not produced, and the longer the operation the greater was the quantity which appeared. . . . It was natural t o account for both these appearances, from the corn- bination of nascent oxygene and hydrogene respectively ; with the nitrogene of the common air dissolved in the water,” Davy was confirmed in his conclusion by experiments in which the electrolytic vessels were placed in a vacuum or in an atmosphere of hydrogen.There was then little or no reddening of the litmus, even after prolonged action of the battery. If nitrogen could be oxidised in this way, the process would be a convenient one for the isolation of’argon, for it could be worked on a large scale aud be made self-acting. But it did not appear a t all probable that nitrogen could take a direct part in the electrolysis. I n that case, its oxidation would be a secondary action, due, perhaps, to the forma- tion of peroxide of hydrogen. This consideration led me to t r y the effect of peroxide of sodium on dissolved nitrogen, but without success.The nitrogen dissolved in 1250 C.C. of tap water and liberated by boiling, was found t o be 19.1 c.c., and i t was not diminished by a previous addition of peroxide of sodium, with or without acid. Having failed in this direction, I endeavoured t o repeat Davy’s experiment * Phil. Tr(tms., 1807, p. 1. VOL. LXXI. 0IS2 T,ORD RAYLEIGH : OBSERVATIONS ON nearly in its original form. bored in a block of paraffin, and connected by a wick of asbestos which had been previously ignited. By means of platinum terminals con- nected with a secondary battery, a potential difference of 100 volts was maintained between the cups. The whole was covered by a glass shade, to exclude any saline matter that might be introduced from the atmosphere, But, under these conditions, no difference in the behaviour of litmus when moistened with water from the two cups could be detected, even after 14 days' exposure to the 100 volts.When, however, the cover was removed, the litmus responded markedly after a day or two. The failure of several attempts of this kind lead me to doubt the correctness of Davy's view, that the dissolved nitrogen of water is oxidised during electrolysis. At any rate, the action is so slow that tho process holds out no promise of usefulness on a large scale. The water mas contained in two cavitie I n the oxidation of nitrogen by gaseous oxygen under the action of electric discharge, a question arises as to the influence of pressure. If the mass absorbed were proportional to pressure, or the volume inde- pendent of psessure, the electrical energy expended being the same, it might be desirable to work with highly condensed gases, in spite of the serious difficulties that must necessarily be encountered.That pressure would be favourable seems probable a p i o r i , and is suggested by certain observations of Dr. Frankland. My own early experiments pointed also in the same direction. A suitable mixture of nitrogen and oxygen, standing in an inverted test-tube over alkali, was sparked from a Rhumhorff coil actuated by five Grove cells; when the total pressure was about three atmospheres, the mass absorbed was about three times that absorbed in the same time at theordinary pressure. This result made i t necessary to proceed to operations upon a larger scale with the a1 ternate current discharge.Experiments were first tried in a small vessel (of 250 c.c.), which would be more easily capable of withstanding internal pressure than a larger one. I n order to protect the glass, which at the top was almost in contact with the electric flame, and to promote absorption of the combined nitrogen, the alkali was used in the form of cz fountain, which struck the glass immediately over the flame, and washed the whole of the internal surface." But, to my surprise, preliminary trials, conducted a t atmospheric pressure, showed that this apparatus was not effective. The rates of absorption were about 1600 C.C. per hour, the runs themselves being for half-an-hour. About double this rate had already been obtained with the same electrical appliances and with stationary alkali.Care having been taken that the quality of the * Rayleigh and Ramsay, Phib. Trans., 1895, p. 217.THE OXInATtON O F NITROGEN GAS. 1s:; mixture within the working vessel was maintained throughout the ruu, the smaller efficiency could only be connected with the coufined space. As to the reason why a confined space should be unfavourable, it is difficult to give a decided opinion. Other things being the same, the surface presented by the alkali mill be diminished in a smaller vessel, and the absorption of the combined nitrogen may consequently be less rapid. But it is difficult to accept this explanation, in view of the favourable conditions secured by the use of a fountain. The gases, as they rise from the flame, impinge directly upon the alkali, which is itself in rapid motion over the whole internal surface.It would almost seem as if the combined nitrogen, as it leaves the flame, is not yet ready for absorption, and only becomes so after the lapse of LZ certain time. However this may be, the efficiency is in practice improved by largely increasing the capacity of the working vessel. A larger bottle, of 370 C.C. capacity, allowed n rate of 2000 C.C. per hour. A flask of still greater capacity gave 3300 C.C. per hour, whilst with a larger globe capable of holding 4; litres, a rate of 6800 C.C. per hour was obtained. These experiments were all made a t atmospheric pressure with a fountain of alkali and with the electric flame in as nearly as possible a constant condition.I n the case of the smallest vessel, i t was thought that the separation of the platinuni terminals may have been insufficient for the best effect, but the loss due to this cause must have been relatively small, Electrical instruments connected with the primary circuit of the Rhumhorff gave readings of 10 amperes and 41 volts. When the comparatively small vessel of 370 C.C. was used a t a pres- sure of about one additional atmosphere, the volume absorbed was about the same as in the experiments with the same vessel a t atmos- pheric pressure, thus indicating a doubled efficiency. This increased efficiency is, however, of no practical importance, inasmuch as a higher efficiency still can be obtained a t atmospheric pressure by use of a larger vessel.I n order to clear up the question, it was necessary to compare the efficiencies in a Inrye vessel a t different pressures, an operation involving considerable difficulty and even danger. For this purpose, a glass globe, nearly spherical in form, and having a capacity of about 7 litres, was employed. The extra pressure was nearly an atmosphere and was obtained by gravity, the feed and return pipes for the alkaline fountain, as well as the pipe for the supply of water to the gas-holder, being carried to a higher level thars that at which the rest of the apparatus stood. The rate of absorption (reduced to atmospheric pressure) was 6880 C.C. per hour. Experiments con- ducted a t atmospheric pressure gave as a mean 6600 C.C. In order to examine still further the influence of pressure, two 0 2184 LORD RAYLEICH : OBSERVATIONS ON experiments were tried under a total pressure of llnrf an atmosphere.The reduced numbers were 5600, 5700 C.C. per hour. From these results, it would appear' that the influence of pressure is slightly favour- able. But, in comparing the results for one atmosphere and for half an atmosphere, it should be remembered that, in the latter case, aqueous vapour is responsible for a sensible part of the total pressure. At any rate, the results are much more nearly independent of pressure than proportional to pressure ; so that the cases of large and small vessels are sharply distinguished, pressure appearing to be advantageous only where the space is too confined to admit of Dhe best efficiency at a given pressure being reached.Not sorry to be relieved from the obligation of designing a Iarge scale apparatus to be worked at a high pressure, such as 20 or 100 atmospheres, I reverted to the ordinary pressure, and sought to obtain n high rate of absorption by employing a powerful electric flame con- tained in cz large vessel whose walls were washed internally by an alkaline fountain. The electrical arrangements have been the subject of much consideration, and require to be different From what would naturally be expected. Since the voltage on the final platinurns during discharge is only from 1600 to 2000, as measured by one of Lord Kelvin's instruments, it might be supposed that a commercial trans- former, transforming from 100 volts. to 2400 volts., would suffice for the purpose.When, however, the attempt is made, it is soon dis- covered that such an arrangement is quite unmanageable. When, after some difficulty, the arc is started, it is found that the electrical con- ditions are unstable. Things may go well for a time, but after perhaps some hours the current will rise and the platinurns will become over- heated and may melt. Even when two transformers were employed, so connected as to give an open secondary circuit nearly 4800 volts., the conditions were not steady enough for convenient practice. The transformer used in the experiments about to be described is by Messrs. Swinburne, and is insulated with oil. On open secondary, the voltage is nearly 8000," but it falls to 2000 or less when the discharge is running.Even with this transformer, it was necessary to include in its primary (thick wire) circuit a self-induction coil, provided with a core consisting of a bundle of iron wires, and adjustable in position. As finally used, the adjustment was such that the electromotive force actually operative on the primary was only about 30 volts. out of the 100 volts. available at the mains of the public supply. This reduction of voltage does not, at any rate from a theoretical point of view, involve any loss of economy, and some such reduction seems to be essential to steadiness. Under these conditions, the current taken amounted to 40 amperes. * Probably 6,000 would have sufficed.THE OXIDATION OF NITROGEN GAS. 185 It is scarcely necessary to say that the watts actually delivered to the primary circuit of tho transformer are less than the number (1200) derived by multiplication of volts.and amp8res. From some experiments made under similar conditions,* I have found that the factor of reduction -the cosine of the angle of lag-is about two-thirds, so that the watts taken in the above arrangement are about 800, representing a little more than a horse-power. The working vessel, A, was of glass, spherical in forin, and of 50 litres capacity. The neck was placed down- wards, and was closed by a large rubber stopper, through which five tubes of glass penetrated. Two tubes of substantial construction carried the electrodes, B, C, arranged much as in a foriner apparatus? ; two more, D and E, were required for the supply tube of the fountain and for the drain of liquid, whilst the fifth, F, was for the supply of gas.The external drown- ing of the vessel, formerly necessary, mas now dispensed with ; but a suitable cool- ing arrangement for the alkali (some- thing like the worm of a condenser) had to be provided to obviate excessive accu- mulation of heat. As the solution of alkali circulated entirely in the closed apparatus, it could lose none of its dissolved argon. I t was maintained in circulation by a small centrifugal pump constructed of iron and driven from an electric motor. The mixed gases (about 11 parts of oxygen to 9 parts of air) were supplied from a large gas-holder; but an auxiliary holder was also necessary in order t o observe the rate of absorption. When the rate became unsatisfactory, the mixed gas in the working vessel was analysed and the necessary rectification effected. In the earlier stages of the operation, the rate of absorption was about 21 litres per hour, and this, by proper attention, could be main- tained without much loss until the accumulation of argon began to tell. If we take 20 litres as corresponding to 800 watts, we have 25 C.C. per watt-hour, an eficiency not very different from that found in operations on a much smaller scale. The present apparatus works about three times as fast as the former one, in which the vessel was smaller and the alkali stationary. .It ’ I hope shortly to publish ail accouiit of the iiietliod cml)lojcd. + liayleigh a i d Rainsay, Pliil. Trans., 1895, 1). 218.186 PERKIN : DERIVATIVES OF MACLURIN. is also more interesting to watch, as the electric flame is fully exposed to view. On the other hand, it is more complicated, owing to the use of a circulating pump, and probably requires closer attention. A failure of the fountain whilst the flame was established mould doubtless soon lead to a disaster. I have been efficiently aided throughout by Mr. Gordon, who has not only fitted the apparatus, but has devised many of the contrivances necessary to meet the ever-recurring difficulties which must be expected in work of this character.