934 
13. These experiments consequently prove in a quantitative way 
that sodium as it has been known up to the present, is also a 
metastable system in consequence of allotropy and that the physical 
and mechanical constants of this metal which have been determined 
hitherto (except the values of the specific heat, mentioned in the 
tables I and II) are entirely fortuitous values. 
14. Some preliminary experiments carried out by Ezer GRIFFITHS 
proved that there exists a measurable difference between the densities 
of a- and g-sodium at the same temperature. We hope to report 
shortly on some dilatometric measurements in this direction. 
Summary of Results. 
Relying on the investigations of Ernst COHEN, HELDERMAN, MOESVELD 
and vAN DEN Boscu and those of E. H. and Ezer Grirrirus on the 
true specific heat of metals at different temperatures we find that: 
1. The true specific heat of sodium is a function of its previous 
thermal history. 
2. Both with the slowly cooled and the chilled metal, at a definite 
temperature detinite and reproducible values of this physical con- 
stant are found. 
3. An intermediate previous thermal history gives values of the 
specific heat between the extremes mentioned under 2. 
4. The experiments of Le Verrier (1892) on the specific heat of 
metals which had not been understood up to the present are cor- 
roborated by the investigations recently carried out with high preci- 
sion by E. H. and Ezer Grirritus. 
5. Sodium is enantiotropic; there exists a transition temperature 
between O° and 90° C. *) 
6. Sodium, as it is known hitherto, is a metastable system as 
might be expected on account of the investigations on bismuth, 
cadmium, copper, zinc, antimony and lead, described some time ago. 
7. All physical and mechanical ‘constants’ known up to the 
present of the metals are entirely fortuitous values; they must be 
redetermined with the pure a-,@-,y-,.... modifications of these 
substances. 
Utrecht, December 1914. yan ’r Horr-Labordatory. 
*) The exact position of this point will be determined by dilatometric measurements. 
