December 30, 1897] 



NATURE 



209 



Nitrons Oxide. 



In preliminary experiments the gas was prepared in the 

 laboratory, at as low a temperature as possible, from nitrate of 

 ammonia, or was drawn from the iron bottles in which it is com- 

 mercially supplied. The purification was by passage over potash 

 and phosphoric anhydride. Unless special precautions are 

 taken the gas so obtained is ten or more milligrams too light, 

 presumably from admixture with nitrogen. In the case of the 

 commercial supply, a better result is obtained by placing the 

 bottles in an inverted position so as to draw from the liqidd 

 rather than from the gaseous portion. 



Higher and more consistent results were arrived at from gas 

 which had been specially treated. In consequence of the high 

 relative solubility of nitrous oxide in water, the gas held in solu- 

 tion after prolonged agitation of the liquid with impure gas from 

 any supply, will contain a much diminished proportion of 

 nitrogen. To carry out this method on the scale required, a 

 large (ii-litre) flask was mounted on an apparatus in connection 

 with the lathe so that it could be vigorously shaken. After the 

 dissolved air had been sufficiently . expelled by preliminary 

 passage of NoO, the water was cooled to near o° C. and violently 

 shaken for a considerable time while the gas was passing in 

 large excess. The nitrous oxide thus purified was expelled 

 from solution by heat, and was used to fill the globe in the 

 usual manner. 



For comparison with the results so obtained, gas purified in 

 another manner was also examined. A small iron bottle, fully 

 charged with the commercial material, was cooled in salt and 

 ice and allowed somewhat suddenly to blow off half its contents. 

 The residue drawn from the bottle in one or other position was 

 employed for the weighings. 



Nitrous Oxide (1896). 

 Aug. 15 Expelled from water ... ... ... ... 3*6359 



„ 17 3"6354 



,, 19 From residue after blow off, valve downwards 3 '6364 



,, 21 ,, ,, valve upwards ... 3*6358 



,,22 ,, „ valve downwards 3*6360 



Mean 



36359 



The mean value may be taken to represent the corrected weight 

 of the gas which fills the globe at o' C. and at the pressure of 

 the gauge (at 15°), corresponding to 2 6276 for oxygen. 



One of the objects which I had in view in determining the 

 density of nitrous oxide was to obtain, if it were possible, 

 evidence as to the atomic weight of nitrogen. It may be re- 

 membered that observations upon the density of pure nitrogen, 

 as distinguished from the atmospheric mixture containing argon 

 which, until recently, had been confounded with pure nitrogen, 

 led ^ to the conclusion that the densities of oxygen and nitrogen 

 were as 16 : i4'oo3, thus suggesting that the atomic weight 

 of nitrogen might really be 14 in place of 1405, as generally 

 received. The chemical evidence upon which the latter number 

 rests is very indirect, and it appeared that a direct comparison 

 of the weight of nitrous oxide and of its contained nitrogen 

 might be of value. A suitable vessel would be filled, under 

 known conditions, with the nitrous oxide, which would then 

 be submitted to the action of a spiral of copper or iron wire 

 rendered incandescent by an electric current. When all the 

 oxygen was removed, the residual nitrogen would be measured, 

 from which the ratio of equivalents could readily be deduced. 

 The fact that the residual nitrogen would possess nearly the 

 same volume as the nitrous oxide from which it was derived 

 would present certain experimental advantages. If, indeed, 

 the atomic weights were really as 14 : 16, the ratio {x) of 

 volumes, after and before operations, would be given by 



2*2996 X X 



whence 



. ^ i_4 



36359 - 2-2996 X ;ir 8' 



= I •0061, 



x=T ^ 36359 



II X 2*2996 



36359 and 2*2996 being the relative weights of nitrous oxide 

 and of nitrogen which (at 0° C. and at the pressure of the 

 gauge) occupy the same volume. The integral numbers for the 

 atomic weights would thus correspond to an expansion, after 

 chemical reduction, of about one-half per cent. 



But in practical operation the method lost most of its ap- 

 parent simplicity. It was found that copper became un- 



1 Rayleigh and Ramsay, Phil. Trans., vol. clxxxvi. p. 190, 1895. 



NO. 1470, VOL. 57] 



manageable at a temperature sufficiently high for the purpose, 

 and recourse was had to iron. Coils of iron suitably prepared 

 and supported could be adequately heated by the current from 

 a dynamo without twisting hopelessly out of shape ; but the use 

 of iron leads to fresh difficulties. The emission of carbonic 

 oxide from the iron heated in vacuum continues for a very long 

 time, and the attempt to get rid of this gas by preliminary 

 treatment had to be abandoned. By final addition of a small 

 quantity of oxygen (obtained by heating some permanganate 

 of potash sealed up in one of the leading tubes) the CO could 

 be oxidised to CO.^, and thus, along with any H2O, be absorbed 

 by a lump of potash placed beforehand in the working vessel. 

 To get rid of superfluous oxygen, a coil of incandescent copper 

 had then to be invoked, and thus the apparatus became rather 

 complicated. 



It is believed that the difficulties thus far mentioned were 

 overcome, but nevertheless a satisfactory concordance in the 

 final numbers was not attained. In the present position of the 

 question no results are of value which do not discriminate with 

 certainty between 14 05 and 14 00. The obstacle appeared to 

 lie in a tendency of the nitrogen to pass to higher degrees of 

 oxidation. On more than one occasion, mercury (-.vhich formed 

 the movable boundary of an overflow chamber) was observed to 

 be attacked. Under these circumstances I do not think it 

 worth while to enter into further detail regarding the 

 experiments in question. 



The following summary gives the densities of the various 

 gases relatively to air, all obtained by the same apparatus.' The 

 last figure is of little significance. 



Air free from HoO and CO2 



Oxygen 



Nitrogen and argon (atmospheric) 



Nitrogen 



Argon 



Carbonic oxide 



Carbonic anhydride 



Nitrous oxide 



I 00000 

 1 10535 

 0*97209 

 096737 



I 37752 

 0-96716 

 1*52909 

 1*52951 



liie value obtained for hydrogen upon the same scale was 

 0*06960 ; but the researches of 3VI. Leduc and of Prof. Morley 

 appear to show that this number is a little too high. 



THE NORTHAM PEBBLE RIDGE. 



'T'HE pebble ridge at Northam is one of the most remarkable 

 -'- examples of littoral drift to be found anywhere round the 

 coast of this country. 



It is thus graphically described by Charles Kingsley ii» 

 " Westward Ho ! " : — " On this pebble ridge the surges of the 

 bay have defeated their own fury by rolling up in the course of 

 ages a rampart of grey boulder stones, some two miles long, as 

 cunningly curved and smoothed and fitted as if the work had 

 been done by human hands, which protect from the high tides 

 of spring and autumn a'fertile sheet of smooth alluvial turf. . . . 

 It was dead calm and yet the air was full of sound— a low deep 

 roar which hovered over downs and broad, salt marsh and river, 

 like the roll of a thousand wheels, the tramp of endless armies, 

 or — what it was — the thunder of a mighty surge upon the 

 boulders of the pebble ridge. . . . The spirit of the Atlantic 

 storm had sent forward the token of his coming in the smooth 

 ground swell which was heard inland two miles away. To- 

 morrow the pebbles, which were now rattling down with each 

 retreating wave, might be leaping to the ridge top and hurled 

 like round shot far ashore upon the marsh by the force of the 

 advancing wave fleeing before the wrath of the western hurri- 

 cane." 



The particulars contained in the following description of this, 

 ridge have been obtained during a recent inspection of this part 

 of the coast of North Devon, and from information obtained 

 from the coastguard and others living in the locality. 



The boulders which compose the ridge have been derived 

 from the cliffs which surmount the shore of Barnstaple Bay, 

 from Hartland Point to Westward Ho, a distance along the 

 coast of about thirteen miles. These cliffs rise to a height of 

 350 feet above the level of the sea between Hartland Point and 

 Clovelly, the height then gradually diminishing towards Wesi - 

 ward Ho, where they terminate. They are composed principally 



"^Roy. Sac. Proc, vol. liii. p. 148, 1893;' vol. Iv. p. 340, 1894; Phii. 

 Trans. 1 vol. clxxxvi. p. 189, 1895 ; Roy. Soc. Proc, vol. lix. p. 201, 1896. 



