TEMPERATURE IN

PLATINUM DEGREES  . copper 70 with manganese 30= Cu2Mn . The product obtained by adding a small quantity of one metal to another has a higher specific resistance than the predominant constituent, but the curve is parallel to, and therefore the same in shape as, that of the latter (cf. the curves for various mixtures of Al and Cu on the chart) . The behaviour of carbon and of insulators like gutta- percha, glass, ebonite, &c., is in complete contrast to the metals, z6 50000 45.000 40000 35.000 30.000 25.000 20.00 1500 10.00 SOD 0000 5.000 0.000 5000 0.000 5.000 0.000 15.000 10.000 5000 4000 3000 2000 1000 Metals . Platinum . Platinum- Gold . Silver . Copper . Iron . rhodium Alloy . Resistance at too° C 39.655 36.87 16.10 8.336 11.572 4.290 o° C 28.851 31.93 11.58 5'990 8.117 2.765 carbonic acid . . .

19.620 .. . . . . liquid

oxygen 7.662 22.17 3.380 1.669 P589 0.633 ,, nitrogen .. . . . . 1'149 oxygen under exhaustion 4.634 20.73 .. . . . . ,, hydrogen . . . 0.826 18.96 0.381 0.244 0.077 0.356 hydrogen under exhaustion 0.7o5 18.90 0.298 0.226 0.071 Resistance coefficients 0.003745 0.003607 0.003903 0.003917 0.004257 0.105515 Vanishing temperatures (Centigrade) -244.500 -543'39° -257.90° -252.26° -225.62° -258.400 C .

-244.15° -530'32° -257.8 -252.25° -226.04 -246.80 D . for their resistivity steadily increases with

cold . The thermoelectric properties of metals at low temperatures are discussed in the article THERMOELECTRICITY . Magnetic Phenomena.—Low temperatures have very marked effects upon the magnetic properties of various substances . Oxygen, long known to be slightly magnetic in the gaseous state, is powerfully attracted in the liquid condition by a magnet, and the same is true, though to a less extent, of liquid air, owing to the proportion of liquid oxygen it contains . A magnet of ordinary carbon steel has its magnetic moment temporarily increased by cooling, that is, after it has been brought to a permanent magnetic condition (" aged ") . The effect of the first immersion of such a magnet in liquid air is a large diminution in its magnetic moment, which decreases still further when it is allowed to warm up to ordinary temperatures . A second cooling, however, increases the magnetic moment, which is again decreased by warming, and after a few repetitions of this cycle of cooling and heating the steel is brought into a condition such that its magnetic moment at the temperature of liquid air is greater by a constant percentage than it is at the ordinary temperature of the air . The increase of magnetic moment seems then to have reached a limit, because on further cooling to the temperature of liquid hydrogen hardly any further increase is observed . The percentage differs with the composition of the steel and with its physical condition . It is greater, for example, with a specimen tempered very soft than it is with another specimen of the same steel tempered glass hard . Aluminium steels show the same kind of phenomena as carbon ones, and the same may be said of chrome steels in the permanent condition, though the effect of the first cooling with them is a slight increase of magnetic moment .

Nickel steels present some curious phenomena . When containing small percentages of nickel (e.g . 0.84 or 3.82), they behave under changes of temperature much like carbon steel . With a sample containing 7.65%, the phenomena after the permanent state had been reached were similar, but the first cooling produced a slight increase in magnetic moment . But steels containing 18.64 and 29% of nickel behaved very differently . The result of the first cooling was a reduction of the magnetic moment, to the extent of nearly 50% in the case of the former . Warming again brought about an increase, and the final condition was that at the temperature of liquid air the magnetic moment was always less than at ordinary temperatures . This anomaly is all the more remarkable in that the behaviour of pure nickel is normal, as also appears to be generally the case with soft and hard iron . Silicon, tungsten and manganese steels are also substantially normal in their behaviour, although there are considerable differences in the magnitudes of the variations they display (Prot . Roy . Soc . Ix .

57 et seq.; also " The Effect of Liquid Air Temperatures on the

Mechanical and other Properties of Iron and its Alloys," by Sir James Dewar and Sir Robert Hadfield, Id. lxxiv . 326-336) . Low temperatures also affect the permeability of iron, i.e. the degree of magnetization it is capable of acquiring under the influence of a certain magnetic force . With fine Swedish iron, carefully annealed, the permeability is slightly reduced by .acling to – 185° C . Hard iron, however, in the same circumstances suffers a large increase of permeability . Unhardenedsteel pianoforte wire, again, behaves like soft annealed iron . As to hysteresis, low temperatures appear to produce no appreciable effect in soft iron; for hard iron the observations are undecisive . Biological Research.—The effect of cold upon the life of living organisms is a matter of great intrinsic interest as well as of wide theoretical importance . Experiment indicates that moderately high temperatures are much more fatal, at least to the lower forms of life, than are exceedingly low ones . Professor M`Kendrick froze for an hour at a temperature of -182° C. samples of meat, milk, &c., in sealed tubes; when these were opened, after being kept at blood-heat for a few days, their contents were found to be quite putrid . More recently some more elaborate tests were carried out at the Jenner (now Lister) Institute of Preventive Medicine on a series of typical bacteria . These were exposed to the temperature of liquid air for twenty hours, but their vitality was not affected, their functional activities remained unimpaired and the cultures which they yielded were normal in every respect .

The same result was obtained when liquid hydrogen was substituted for air . A similar persistence of life has been demonstrated in seeds, even at the lowest temperatures; they were frozen for over too hours in liquid air at the instance of Messrs

Brown and Escombe, with no other effect than to afflict their protoplasm with a certain inertness, from which it recovered with warmth . Subsequently commercial samples of barley, peas and vegetable-marrow and mustard seeds were literally steeped for six hours in liquid hydrogen at the Royal Institution, yet when they were sown by Sir W . T . Thiselton Dyer at Kew in the ordinary way, the proportion in which germination. occurred was no smaller than with other batches of the same seeds which had suffered no abnormal treatment . Mr Harold Swithinbank has found that exposure to liquid air has little or no effect on the vitality of the tubercle bacillus, although by very prolonged exposures its virulence is modified to some extent; but alternate exposures to normal and very cold temperatures do have a decided effect both upon its vitality and its virulence . The suggestion once put forward by Lord Kelvin, that life may in the first instance have been conveyed tq,this planet on a meteorite, has been objected to on the ground that any living organism would have been killed before reaching the earth by its passage through the intense cold of interstellar space; the above experiments on the resistance to cold offered by seeds and bacteria show that this objection at least is not fatal to Lord Kelvin's idea . At the Lister Institute of Preventive Medicine liquid air has been brought into use as an agent in biological research . An inquiry into the intracellular constituents of the typhoid bacillus, initiated under the direction of Dr Allan Macfadyen, necessitated the separation of the cell-plasma of the organism . The method at first adopted for the disintegration of the bacteria was to mix them with silver-sand and churn the whole up in a closed vessel in which a series of horizontal vanes revolved at a high speed . But certain disadvantages attached to this procedure, and accordingly some means was sought to do away with the sand and triturate the bacilli per se . This was found in liquid air, which, as had long before been shown at the Royal Institution, has the power of reducing materials like grass or the leaves of plants to such a state of brittleness that they can easily be r6 powdered in a mortar .

By its aid a complete trituration of the typhoid bacilli has been accomplished at the Jenner Institute, and the same

process, already applied with success also to yeast cells and animal cells, is being extended in other directions . Industrial Applications.—While liquid air and liquid hydrogen are being used in scientific research to an extent which increases every day, their applications to industrial purposes are not so numerous . The temperatures they give used as simple refrigerants are much lower than are generally required industrially, and such cooling as is needed can be obtained quite satisfactorily, and far more cheaply, by refrigerating machinery employing more easily condensable gases . Their use as a source of motive power, again, is impracticable for any ordinary purposes, on the score of inconvenience and expense . Cases may be conceived of in which for special reasons it might prove advantageous to use liquid air, vaporized by heat derived from the surrounding atmosphere, to drive compressed-air engines, but any advantage so gained would certainly not be one of cheapness . No doubt the power of a waterfall running to waste might be temporarily conserved in the shape of liquid air, and thereby turned to useful effect . But the reduction of air to the liquid state is a process which involves the expenditure of a very large amount of energy, and it is not possible even to recover all that expended energy during the transition of the material back to the gaseous state . Hence to suggest that by using liquid air in a motor more power can be developed than was expended in producing the liquid air by which the motor is worked, is to propound a fallacy worse than perpetual motion, since such a process would have an efficiency of more than l00% . Still, in conditions where economy is of no account, liquid air might perhaps, with effectively isolated storage, be utilized as a motive power, e.g. to drive the engines of submarine boats and at the same time provide a supply of oxygen for the crew; even without being used in the engines, liquid air or oxygen might be found a convenient form in which to store the air necessary for respiration in such vessels . But a use to which liquid air machines have already been put to a large extent is for obtaining oxygen from the atmosphere . Although when air is liquefied the oxygen and nitrogen are condensed simultaneously, yet owing to its greater volatility the latter boils off the more quickly of the two, so that the remaining liquid becomes gradually richer and richer in oxygen . The fractional distillation of liquid air is the method now universally adopted for the preparation of oxygen on a commercial scale, while the nitrogen simultaneously obtained is used for the production of cyanamide, by its action on carbide of calcium .

An interesting though

minor application of liquid oxygen, or liquid air from which most of the nitrogen has evaporated, depends on the fact that if it be mixed with powdered charcoal, or finely divided organic bodies, it can be made by the aid of a detonator to explode with a violence comparable to that of dynamite . This explosive, which might properly be called an emergency one, has the disadvantage that it must be prepared on the spot where it is to be used and must be fired without delay, since the liquid evaporates in a short time and the explosive power is lost; but, on the other hand, if a charge fails to go off it has only to be left a few minutes, when it can be withdrawn without any danger of accidental explosion . For further information the reader may consult W . L . Hardin, Rise and Development of the Liquefaction of Gases (New York, 1899), and Lefevre . La Liquifaction des gaz et ses applications; also the article CONDENSATION OF GASES . But the literature of liquid gases is mostly contained in scientific periodicals and the proceedings of learned societies . Papers by Wroblewski and Olszewski on the liquefaction of oxygen and nitrogen may be found in the Comptes rendus, vols. xcvi.-cii., and there are important memoirs by the former on the relations between the gaseous and liquid states and on the compressibility of hydrogen in Wien . Akad..Sitzber. vols. xciv. and xcvii.; his pamphlet Comme l'air a ete liquejii (Paris, 1885) should also be referred to . For Dewar's work, see Proc . Roy . Inst. from 1878 onwards, including " Solid Hydrogen " (19o0) ; " Liquid Hydrogen Calorimetry " (19o4); " New Low Temperature Phenomena " (1905) ; " Liquid Air and Charcoal at Low Temperatures " (1906) ; " Studies in High Vacua and Helium at Low Temperatures " (19o7); also " The Nadir of Temperature and Allied Problems " (Bakerian Lecture), Proc .

Roy . Soc . (1901), and the Presidential Address to the

British Association (1902) . The researches of Fleming and Dewar on the electrical and magnetic properties of substances at low temperatures are described in Proc . Roy . Soc. vol . Ix., and Proc . Roy . Inst . (1896) ; see also " Electrical Resistance of Pure Metals, Alloys and Non-Metals at the Boiling-point of Oxygen," Phil . Mag. vol. xxxiv . (1892) ; " Electrical Resistance of Metals and Alloys at Temperatures approaching the Absolute Zero," ibid. vol. xxxvi .

(1893); " Thermoelectric

Powers of Metals and Alloys between the Temperatures of the Boiling-point of Water and the Boiling-point of Liquid Air, '' ibid. vol. xl . (1895) ; and papers on the dielectric constants of various substances at low temperatures in Proc . Roy . Soc. vols . Ixi. and lxii . Optical and spectroscopic work by Liveing and Dewar on liquid gases is described in Phil . Mag. vols. xxxiv . (1892), xxxvi . (1893), xxxviii . (1894) and xl . (1895); for papers by the same authors on the separation and spectroscopic examination of the most volatile and least volatile constituents of atmospheric air, see Proc . Roy .

Soc. vols. lxiv., lxvii. and lxviii . An account of the influence of very low temperatures on the germinative power of seeds is given by H . T . Brown and F . Escombe in Proc . Roy . Soc. vol . Ixii., and by Sir W . Thiselton Dyer, ibid. vol. lxv., and their effect on bacteria is discussed by A . Macfadyen, ibid. vols. lxvi. and lxxi . (J .