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TEMPERATURE IN PLATINUM DEGREES

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Originally appearing in Volume V16, Page 759 of the 1911 Encyclopedia Britannica.
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TEMPERATURE IN See also:

PLATINUM DEGREES . See also:copper 70 with See also:manganese 30= Cu2Mn. The product obtained by adding a small quantity of one See also:metal to another has a higher specific resistance than the predominant constituent, but the See also: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 See also:chart). The behaviour of See also:carbon and of insulators like See also:gutta- percha, See also:glass, ebonite, &c., is in See also: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- See also:Gold. See also:Silver. Copper. See also:Iron. See also: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 See also:acid . . .

19.620 .. .. . . liquid See also:

oxygen 7.662 22.17 3.380 1.669 P589 0.633 ,, See also:nitrogen .. .. .. 1'149 oxygen under exhaustion 4.634 20.73 .. .. .. ,, See also: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 See also:

cold. The thermoelectric properties of metals at See also:low temperatures are discussed in the See also:article See also:THERMOELECTRICITY. Magnetic Phenomena.—Low temperatures have very marked effects upon the magnetic properties of various substances. Oxygen, See also:long known to be slightly magnetic in the gaseous See also:state, is powerfully attracted in the liquid See also:condition by a magnet, and the same is true, though to a less extent, of liquid See also:air, owing to the proportion of liquid oxygen it contains. A magnet of See also:ordinary carbon See also: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 See also: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 See also:cycle of cooling and See also:heating the steel is brought into a condition such that its magnetic moment at the temperature of liquid air is greater by a See also: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 See also:composition of the steel and with its See also: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. See also:Aluminium steels show the same See also: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.

See also:

Nickel steels See also: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 See also: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 See also: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 See also: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. See also:Silicon, See also:tungsten and manganese steels are also substantially normal in their behaviour, although there are considerable See also:differences in the magnitudes of the See also:variations they display (Prot. See also:Roy. See also:Soc. Ix.

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

Mechanical and other Properties of Iron and its See also:Alloys," by See also:Sir See also:James See also:Dewar and Sir See also:Robert Hadfield, Id. lxxiv. 326-336). Low temperatures also affect the See also:permeability of iron, i.e. the degree of magnetization it is capable of acquiring under the See also:influence of a certain magnetic force. With See also:fine See also: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 See also:pianoforte See also:wire, again, behaves like soft annealed iron. As to See also:hysteresis, low temperatures appear to produce no appreciable effect in soft iron; for hard iron the observations are undecisive. Biological See also:Research.—The effect of cold upon the See also:life of living organisms is a See also:matter of See also:great See also:intrinsic See also:interest as well as of wide theoretical importance. Experiment indicates that moderately high temperatures are much more fatal, at least to the See also:lower forms of life, than are exceedingly low ones. See also:Professor M`Kendrick froze for an See also:hour at a temperature of -182° C. samples of See also:meat, See also:milk, &c., in sealed tubes; when these were opened, after being kept at See also:blood-See also:heat for a few days, their contents were found to be quite putrid. More recently some more elaborate tests were carried out at the See also:Jenner (now See also:Lister) See also:Institute of Preventive See also:Medicine on a See also:series of typical bacteria. These were exposed to the temperature of liquid air for twenty See also: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 See also:

Brown and See also:Escombe, with no other effect than to afflict their See also:protoplasm with a certain inertness, from which it recovered with warmth. Subsequently commercial samples of See also:barley, peas and See also:vegetable-marrow and See also: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 See also:Dyer at See also: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 See also:suggestion once put forward by See also:Lord See also:Kelvin, that life may in the first instance have been conveyed tq,this See also:planet on a See also:meteorite, has been objected to on the ground that any living organism would have been killed before reaching the See also: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 See also:idea. At the Lister Institute of Preventive Medicine liquid air has been brought into use as an See also:agent in biological research. An inquiry into the intracellular constituents of the typhoid bacillus, initiated under the direction of Dr See also:Allan Macfadyen, necessitated the separation of the See also:cell-plasma of the organism. The method at first adopted for the disintegration of the bacteria was to mix them with silver-See also:sand and See also:churn the whole up in a closed See also:vessel in which a series of See also:horizontal vanes revolved at a high See also:speed. But certain disadvantages attached to this See also: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 See also:power of reducing materials like grass or the leaves of See also:plants to such a state of brittleness that they can easily be r6 powdered in a See also:mortar.

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

process, already applied with success also to yeast cells and See also:animal cells, is being extended in other directions. See also:Industrial Applications.—While liquid air and liquid hydrogen are being used in scientific research to an extent which increases every See also:day, their applications to industrial purposes are not so numerous. The temperatures they give used as See also: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 See also:refrigerating machinery employing more easily condensable gases. Their use as a source of See also:motive power, again, is impracticable for any ordinary purposes, on the See also:score of inconvenience and expense. Cases may be conceived of in which for See also:special reasons it might prove advantageous to use liquid air, vaporized by heat derived from the surrounding See also:atmosphere, to drive compressed-air engines, but any See also:advantage so gained would certainly not be one of cheapness. No doubt the power of a See also:waterfall See also:running to See also: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 See also:expenditure of a very large amount of See also: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 See also:developed than was expended in producing the liquid air by which the motor is worked, is to propound a See also:fallacy worse than perpetual See also:motion, since such a process would have an efficiency of more than l00%. Still, in conditions where See also:economy is of no See also: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 See also:time provide a See also:supply of oxygen for the See also:crew; even without being used in the engines, liquid air or oxygen might be found a convenient See also:form in which to See also:store the air necessary for respiration in such vessels. But a use to which liquid air See also: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 See also:distillation of liquid air is the method now universally adopted for the preparation of oxygen on a commercial See also:scale, while the nitrogen simultaneously obtained is used for the See also:production of See also:cyanamide, by its See also:action on See also:carbide of See also:calcium.

An interesting though See also:

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 See also: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 See also: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 See also:short time and the explosive power is lost; but, on the other See also:hand, if a See also:charge fails to go off it has only to be See also:left a few minutes, when it can be withdrawn without any danger of accidental See also:explosion. For further See also:information the reader may consult W. L. Hardin, Rise and Development of the Liquefaction of Gases (New See also:York, 1899), and Lefevre. La Liquifaction See also:des gaz et ses applications; also the article CONDENSATION OF GASES. But the literature of liquid gases is mostly contained in scientific See also:periodicals and the proceedings of learned See also: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 See also: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 (See also:Paris, 1885) should also be referred to. For Dewar's See also:work, see Proc. Roy. Inst. from 1878 onwards, including " Solid Hydrogen " (19o0) ; " Liquid Hydrogen See also:Calorimetry " (19o4); " New Low Temperature Phenomena " (1905) ; " Liquid Air and Charcoal at Low Temperatures " (1906) ; " Studies in High Vacua and See also:Helium at Low Temperatures " (19o7); also " The See also:Nadir of Temperature and Allied Problems " (Bakerian Lecture), Proc.

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

British Association (1902). The researches of See also:Fleming and Dewar on the See also: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 See also:Absolute Zero," ibid. vol. See also:xxxvi.

(1893); " Thermoelectric See also:

Powers of Metals and Alloys between the Temperatures of the Boiling-point of See also:Water and the Boiling-point of Liquid Air, '' ibid. vol. xl. (1895) ; and papers on the See also:dielectric constants of various substances at low temperatures in Proc. Roy. Soc. vols. Ixi. and lxii. See also: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.

End of Article: TEMPERATURE IN PLATINUM DEGREES

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