82 PHYSICS OF MATTER 



based firmly on the laws of thermodynamics the absolute scale of 

 temperature, as we know it to-day. 



The absolute zero of temperature has to the physicist all the fasci- 

 nation that the North Pole has to Arctic explorers, and is probably 

 even more difficult to attain. Yet steady progress has been made 

 in conquering the difficult territory that lies toward this goal. The 

 experimental efforts to liquefy the more refractory gases showed that 

 far lower temperatures than had previously been reached must be 

 employed; and step by step, following the suggestions of thermo- 

 dynamics, the means of attaining low temperatures have been im- 

 proved, at first cooling by adiabatic expansion of more compressible 

 gases, then aided by the sudden expansion of the gas itself which 

 had been compressed and cooled, and then by a continuous self- 

 intensive action, in which the cold produced by the expansion of one 

 portion of the compressed gas was made use of to cool the still unex- 

 panded gas as it approached the point of expansion. 



The mere record of the temperatures reached marks a series of 

 triumphs of ingenuity and perseverance. Thus Faraday, in 1845, 

 reached a temperature of 110 by the use of solid carbon dioxide 

 and ether evaporated at low pressure. Pictet in 1877 reached 140, 

 and liquefied oxygen under pressure. Olszewski in 1885 obtained a 

 temperature of 225 by the evaporation of a mass of solid nitrogen. 

 In 1898 Dewar obtained liquid hydrogen boiling at 252, or only 

 20.5 above the absolute zero, and later by boiling at reduced pres- 

 sures he was able to obtain 259.5 or 13.5 degrees absolute scale, 

 at which point hydrogen is frozen solid. 



The attainment of these low temperatures has not alone made 

 possible investigations of the greatest interest to the physicist, 

 such as studies of the magnetic and electric properties of bodies as 

 they approach the absolute zero, but has enabled the effect of extreme 

 cold on chemical actions to be determined, and has led to the inter- 

 esting conclusion that "The great majority of chemical interactions 

 are entirely suspended." Though it has been shown by Dewar and 

 Moissan that in case of solid hydrogen and liquid fluorine, violent 

 reaction still takes place even at that small remove from the absolute 

 zero. 



A very interesting field has also been opened to biological research, 

 in the effect of extreme cold on the vitality of seeds and micro- 

 organisms. It was found, for example, that barley, pea, and mustard 

 seeds steeped for six hours in liquid hydrogen and thus kept at a tem- 

 perature of minus 252 degrees, showed no loss of vitality. So, also, 

 certain micro-organisms, among others the bacilli of typhoid fever, 

 Asiatic cholera, and diphtheria, were kept by MacFadyen for seven 

 days at the temperature of liquid air without appreciable loss of 

 vitality. It has been suggested by Professor Travers that, "It is 



