^44 



A^A TJJRE 



[July 4, 1901 



reduced by the Callendar and Dickson methods. A table was 

 given showing the results for seven thermometers, viz., two 

 of platinum, one of gold, silver, copper and iron, and one of 

 platinum-rhodium alloy. 



It is noted that the lowest boiling point for hydrogen was given 

 by the gold thermometer. Next to it came one of the platinum 

 thermometers, and then silver, while copper and the iron difter 

 from the gold value by 26 and 32 degrees respectively. The 

 gold thermometer would make the boiling point 23°'5 instead of 

 the 20°'5 given by the gas thermometer. Then the reduction 

 of temperature under exhaustion amounts to only 1° instead of 4° 

 as given by the gas thermometer. The extraordinary reduction in 

 resistance of some of the metals at the boiling point of hydrogen 

 is very remarkable. Thus copper has only i/i05th, gold i/jOth, 

 platinum i/3Sth to l/l7th, silver i/24th the resistance at melt- 

 ing ice, whereas iron is only reduced to i/Sth part of the same 

 initial resistance. The real law correlating electric resistance 

 and temperature within the limits we are considering is unknown, 

 and no thermometer of this kind can be relied im for giving 

 accurate temperatures up to and below the boiling point of 

 hydrogen. The curves are discussed in the paper, and I am 

 indebted to Mr. J. II. D. Dickson and Mr. J. E. Petavel for help 

 in this part of the work. 



Helium separated from the gas of the King's Well, Bath, and 

 purifiedby passing through a U-tube immersed in liquid hydrogen, 

 was filled directly into the ordinary form of Cailletet gas receiver 

 used with his apparatus and subjected to a pressure of So atmo- 

 spheres, while a portion of the narrow part of the glass tube was 

 immersed in liquid hydrogen. On sudden expansion from this 

 pressure to .atmospheric pressure a mist from the production of 

 some solid body was clearly visible. After several compressions 

 and expansions, the end of the tube contained a small amount of 

 a solid body that passed directly into gas when the liquid hydro- 

 gen was removed and the tube kept in the vapour of hydrogen 

 above the liquid. On lowering the temperature of the liquid 

 hydrogen by exhaustion to its melting point, which is about 16° 

 absolute, and repeating the expansions on the gas from which 

 the solid had separated by the previous expansions at the boiling 

 point or 2o°'5, 710 mist was seen. From this it appears the mist 

 was caused by some other material than helium, in all proba- 

 bility neon, and when the latter is removed no mist is seen, 

 when the gas is expanded from 80 to 100 atmospheres, even 

 although the tube is surrounded with solid hydrogen. From 

 experiments made on hydrogen that had been similarly purified 

 like the helium and used in the same apparatus, it appears a 

 mist can be seen in hydrogen (under the same conditions of 

 expansion as applied to the helium sample of gas) when the 

 initial temperature of the expanding gas was twice the critical 

 temperature, but it was not visible when the initial temperature 

 was about two and a half times the critical temperature. 

 This experience applied to interpret the helium experi- 

 ments would make the critical temperature of the gas under 

 9° absolute. 



Olszewski in his experiments expanded helium from about 

 seven times the critical temperature under a pressure of 125 

 atmospheres. Jf the temperature is calculated from the adia- 

 batic expansion starting at 21' absolute, an effective expansion 

 of only 20 to I would reach 6° '3, and 10 to 1 of S°'3. It is now 

 safe to say, helium has been really cooled to 9" or 10" absolute 

 without any appearance of liquefaction. There is one point, 

 however, that must be con.sidered, and that is the small re- 

 fractivity of helium as compared to hydrogen, which, as Lord 

 Rayleigh has shown, is not more than one-fourth the latter gas. 

 Now as the liquid refractivities are substantially in the same 

 ratio as the gaseous refractivities in the case of hydrogen and 

 oxygen, and the refractive index of liquid hydrogen is about 

 1'I2, then the value for liquid helium should be about i'03, 

 both taken at their respective boiling points. In other words, 

 liquid helium at its boiling point would have a refractive index 

 of about the same value as liquid hydrogen at its critical point, 

 and as a consequence, small drops of liquid helium forming in 

 the gas near its critical point would be far more difficult to see 

 than in the case of hydrogen similarly situated. 



The hope of being able to liquefy helium, which would appear 

 to have a boiling point of about 5° absolute, or one-fourth that 

 of liquid hydrogen, is dependent on subjecting helium to the 

 same process that succeeds with hydrogen ; only instead of using 

 liquid air under exhaustion as the primary cooling agent, liquid 

 hydrogen under exhaustion must be employed, and the resulting 

 liquid collected in vacuum vessels surrounded with liquid hydro- 



NO. 1653, VOL. 64] 



gen. The following table embodies the results of experience 

 and theory : — 



The first column gives the initial temperature before con- 

 tinuous expansion through a regenerator, the second the critical 

 point of the gas that can be liquefied under such conditions, and 

 the third the boiling point of the resulting liquid. It will be 

 seen that by the use of liquid or solid hydrogen as a cooling 

 agent we ought to be able to liquefy a body having a critical 

 point of about 6° to S' absolute and boiling point of 

 about 4° or 5° absolute. Then, if liquid helium could be 

 produced with the probable boiling point of 5° absolute this 

 substance would not enable us to reach the zero of temperature ; 

 another gas must be found that is as much more volatile than 

 helium as it is than hydrogen in order to reach w'ithin i' of the 

 zero of temperature. If the helium group comprises a substance 

 having the atomic weight 2, or half that of helium, such a gas 

 would bring us nearer the desired goal. In the meantime the 

 production of liquid helium is a difficult and expensive enough 

 problem to occupy the scientific world for many a day. 



A number of miscellaneous observations have been made in the 

 course of this inquiry, among which the following may be men- 

 tioned. Thus the great increase of phosphorescence in the case 

 of organic bodies cooled to the boiling point of hydrogen under 

 light stimulation is very marked, when compared with the same 

 effects, brought about by the use of liquid air. A body like 

 sulphide of zinc cooled to 21° absolute and exposed to light 

 shows brilliant phosphorescence on the temperature being 

 allowed to rise. Bodies like radium that exhibit self-luminosity 

 in the dark, cooled in liquid hydrogen maintain their luminosity 

 unimpaired. Photographic action is still active although it is 

 reduced to about half the intensity it bears at the temperature 

 of liquid air. Some crystals when placed in liquid hydrogen 

 become for a time self-luminous, on account of the high electric 

 stimulation brought about by the cooling causing actual electric 

 discharges between the crystal molecules. This is very marked 

 with some platino-cyanides and nitrate of uranium. Even 

 cooling such crystals to the temperature of liquid air is suffi- 

 cient to develop marked electrical and luminous effects. 



Considering that both liquid hydrogen and air are highly 

 insulating liquids, the fact of electric discharges taking place 

 under such conditions proves that the electric potential generated 

 by the cooling must be very high. When the cooled crystal is 

 taken out of either liquid and allowed to increase in temperature, 

 the luminosity and electric discharges take place again during 

 the return to the normal temperature. A crystal of nitrate of 

 uranium gets so highly charged electrically that, although its 

 density is 2'S and that of liquid air about I, it refuses to sink, 

 sticking to the side of the vacuum vessel and requiring a marked 

 pull on a silk thread, to which it is attached, to displace it. 

 Such a crystal rapidly removes cloudiness from liquid air by 

 attracting all the suspended particles on to its surface. The 

 study of pyro-electricity at low temperatures will solve some 

 very important problems. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 

 The Education Bill has been abandoned by the Government 

 on account of want of time to consider it adequately during the 

 present session. A short measure dealing with the difficulties 

 which have arisen in connection with the recent judginent as to 

 higher elementary schools and evening continuation schools was 

 introduced in the House of Commons on Tuesday, and it is 

 hoped that the second reading will be taken early next week. 

 The measure proposes to empower county or county borough 

 councils, or technical instruction committees, to make arrange- 

 ments with School Boards for the continuation during one year 

 of the work to which school funds have been declared to be in- 

 applicable by the Cockerton judgment. Sir Joshua Fitch 



