1903.] 



on Low Temperature Investigations. 



425 



state such films, when struck with a cork hammer, give out a clear 

 metallic ring, and if the striking is continued during the heating up 

 of the film, a complete gamut of notes is produced from the varying 

 elasticity. After returning to the ordinary temperature the film 

 recovers all its ordinary properties. 



Molecular Volumes at the Zero of Temperature, 



Theoretical formulae enable an estimate to be formed of the 

 volume of the gram-molecule of many bodies at the zero of tempera- 

 ture. The direct experimental method is to ascertain the densities 

 of bodies as near the zero of temperature as possible. By means of 

 the use of liquid hydrogen as a cooling agent instead of liquid air 

 densities might be determined within 20° of the zero. In the mean- 

 time the limiting densities of oxygen, nitrogen and hydrogen have 

 been found, together with the coefficients of expansion about their 

 boiling points. The approximate results are given in the following 

 table : — 



Table II. 



Oxygen 



Nitrogen 



Hydrogen 



Density Density 



at Boiling at 



Point. 62-5° Ab. 



112 



0-80 

 0-07 



1-24 



0-88 



Density 



at 

 20° Ab. 



Density 



at 

 15° Ab. 



0-076 



Coefficient 



of 

 Expansion. 



■004 

 •006 

 •01.3 



Thus solid oxygen and nitrogen are respectively some 18 and 14 

 times denser than solid hydrogen, while the expansion coefficients of 

 oxygen, nitrogen and hydrogen are roughly in the ratio of 1, 1^ and 3. 

 With these values the molecular volumes at the absolute zero can be 

 infeired, if we assume the general application of what is called the 

 Matthias Law of the rectilinear semi-diameter. The values which 

 result for oxygen, nitrogen and hydrogen are respectively 21 • 2, 25 * 5, 

 24 "2. The volume in cubic centimetres of the gram-molecule of 

 these three elements does not differ much from the mean value 23 • 6 c.c. 

 The experiments already described on the density of ice and solid 

 carbonic acid, about 90° absolute, enables an approximate estimate 

 to be made of their zero volumes, which results in the values of 19 '2 

 for the ice molecule and 25 • 7 for the carbonic acid one. From these 

 values along with the molecular volumes given above for solid 

 hydrogen and oxygen, we can ascertain the volume change that would 

 result in the formation of the compound molecules of ice and solid 

 carbonic acid — provided they could be formed by an imaginary com- 

 bination taking place, at the zero of the solid hydrogen and oxygen 

 on the one hand, and the solid oxygen and carbon on the other. Thus 



