Jzuie 2, 1887] 



NATURE 



105 



concentric flames now employed. The dome is of rolled 

 copper, the plinth or base of massive cast-iron lined with 

 iron sheets. The cost of such a lantern is about ^1700. 

 The lantern of recent lightships has been treated in the 

 same way, having regard to its lightness, mobility, and 

 smaller dimensions. The diameter has been extended 

 to 8 feet, the height of plate-glass to 4 feet, the 

 cylindrical form substituted for every other. 



It does not seem possible to construct lighthouse towers 

 and lanterns of better designs and materials than those 

 which have been described. An important amplification 

 of the dimensions may, however, be resorted to in the 

 future to meet the increasing radii of the lenticular appar- 

 atus, and the increasing size and height of the central 

 flames. This is on the assumption that electricity does 

 not displace petroleum and gas as illuminants. It may 

 be counted as an additional claim of the arc to be the 

 light of the future that it requires no apparatus larger 

 than Fresnel's first order of 920 millimetres focal dis- 

 tance, and that therefore no lantern exceeding 14 feet in 

 diameter with 10 feet of glazing, and no tower with a 

 diameter of platform greater than 23 feet, would 

 certainly be needed. The merits and prospects of the 

 rival illuminants will be discussed in a subsequent 

 article. J. Kenward 



(To be continued.) 



CONDENSATION OF GASES. 



A MONG the numerous subjects which have en- 

 ■**■ grossed the attention of the knowledge-seekers of 

 the present century, probably none have surpassed in 

 fascination and in the wealth of results which have 

 followed persistent effort the question of the possibility 

 of liquefying those gases which for ages had been con- 

 sidered permanent. Immediately after that epoch-making 

 period in chemistry and physics, when Faraday, following 

 in the footsteps of Northmore who in 1806 had succeeded 

 in liquefying chlorine, announced to the world the fruitful 

 results of his experiments upon the liquefaction of gaseous 

 sulphurous, carbonic, and hydrochloric acids, nitrous 

 oxide, cyanogen, and ammonia, came a long interval, 

 during which all attempts to induce hydrogen, oxygen, 

 nitric oxide, marsh gas, and carbon monoxide to take 

 up the liquid state yielded little more than negative 

 results, and the subject appeared almost without hope. 

 When one looks back to the end of the year 1877 and 

 remembers the thrill of excitement which ran through 

 the civilized world when the double announcement was 

 made by the French Academicians that oxygen had been 

 independently liquefied by Cailletet and Pictet, and then, 

 in the mind's eye, reverts to the long years of trial and 

 experiment during which these and other workers were 

 slowly but surely building up future success on present 

 failure, one cannot but be cheered by the thought that 

 patient work inevitably brings its own reward. The 

 fundamental principle upon which both based their ex- 

 periments was, that the gases must be simultaneously 

 exposed to very high pressures and to temperatures lower 

 than their critical points. Pictet, whose apparatus was a 

 triumph of mechanical skill, evolved his gas to be liquefied 

 from a strong wrought-iron cylinder, from whence it passed 

 into a closed copper tube surrounded by a cold bath of 

 rapidly evaporating liquefied carbon dioxide, which re- 

 duced the temperature to -130° C. Cailletet arrived at 

 the same end by using a hydraulic press to compress his 

 gas, but instead of using a very cold bath he caused the 

 gas to effect its own reduction of temperature by suddenly 

 releasing the pressure, causing rapid evaporation, and 

 hence such a considerable cooling that the gis condensed 

 in drops of liquid. Pictet, on January 10, 1878, further 

 succeeded in crowning his results by liquefying hydrogen 

 at a pressure of 650 atmospheres and at a temperature of 



- 140'', and finally, on releasing the pressure, by actually 

 solidifying the hydrogen, which fell " like so many drops 

 of steel " upon the ground. 



But now came the question of the possibility of pro- 

 ducing still lower temperatures, so as to effect the same 

 result at correspondingly lower pressures, and so success- 

 ful have efforts in this direction been that the more per- 

 manent gases have at last been liquefied at pressures 

 nearly approaching atmospheric, and retained in the 

 liquid form under even less than atmospheric pressure. 

 This is a great leap in advance, for it not only enables us 

 to determine the boiling-points of the liquefied gases at 

 ordinary pressure, but also to determine their densities in 

 strictly comparable numbers. This happy consummation 

 we mainly owe to the untiring efforts of Dr. K. Olszewski, 

 whose latest results have just been given to the world, 

 and a short description of whose work will probably be of 

 general interest. 



The most critical portion of any apparatus for such a 

 purpose is of necessity the glass tube in which the lique- 

 faction is to occur, the capacity of which for withstanding 

 rapid changes of both temperature and pressure is put to 

 the severest test. Olszewski paid particular attention to 

 the preparation of his tube, heating it for some time 

 almost to redness in an iron tube packed with calcined 

 magnesia, and allowing it to cool slowly beneath a thick 

 layer of hot ashes, thereby obtaining a tube in which more 

 than a hundred experiments were performed without a 

 single explosion. The open end of this tube, a, was 

 attached to a brass flange, b, the upper part of which 

 was furnished with two openings, one for the hydrogen 

 thermometer, whose bulb reached to the bottom of a, the 

 other uniting the tube a with a branched copper tube e, 

 by means of which connexion could be made at pleasure 

 with (i) the manometer /, for use with pressures smaller 

 than atmospheric, (2) an air-manometer, g., for use with 

 higher pressures, (3) a large air-pump for reducing the 

 pressure upon the liquefied gas, (4) an aspirator, r, used 

 as afterwards described in the density determinations, 

 and (5) an iron Natterer cylinder, /, in which the gas to 

 be liquefied was stored up under a pressure of 60-80 

 atmospheres. A caoutchouc stopper, /', held the lique- 

 faction tube within a system of glass cylinders designed 

 for the reception of liquid ethylene, which was used to 

 effect the reduction of temperature, and for preserving 

 the same from the warming influence of the surrounding 

 air. The four vessels were held within each other without 

 touching by pieces of cork and felt rings, so that the 

 ethylene was separated from the surrounding air by 

 badly conducting layers of air, and the evaporated ethyl- 

 ene, passing in the direction of the arrows between the 

 walls, still further counteracted the influence of radiation 

 from warmer surroundings. In the outer cylinder were 

 placed a few pieces of chloride of calcium in order to dry 

 the air and prevent the deposition of hoar frost. The 

 liquid ethylene was supplied from a second Natterer 

 cylinder, /, fitted with a siphon arrangement and placed 

 in a mixture of ice and salt ; on the way to its receptacle 

 the ethylene passed through a spiral copper tube sur- 

 rounded by a freezing mixture of solid carbon dioxide 

 and ether contained in a double-walled vessel, m. On 

 connecting the vessel with the air-pump and reducing the 

 pressure, the temperature of this freezing mixture sank 

 to — 100°, and 150 c.c. of liquid ethylene were obtained, 

 which remained perfectly quiet for hours under atmo- 

 spheric pressure. The glass tube n was then connected 

 with the air-pump, by means of which the pressure was 

 reduced until the ethylene began to boil ; here however a 

 difficulty, for a long time insurmountable, presented itself; 

 for it was found that inequalities of temperature in the 

 ethylene column caused violent disturbances, and the 

 liquid rapidly disappeared out of the vessel. A simple 

 expedient, however, that of forcing a regulated stream of 

 dry air through the ethylene, was eventually hit upon and 



