1115 
temperature it is solid), the large differences (159 units) are observed 
again *). 
7. If we consider the phenomena with one of the dilatometers 
(for example with N°. 1) it is evident that at the constant temperature 
of 59°.8 C. there occurs an increase of volume (287 units). Some 
time later the volume at 59°.6 C. is 183 units greater than before 
at 59°.8 C. although the temperature is lower (0°.2). 
8. Considering that in the second dilatometer also the same 
phenomena occurred at 59°.8 C. [the volume increases at constant 
temperature (345 units) and is afterwards at 59°.6 C. greater (227 
units) than before at a temperature which is 0°.2 lower| we may 
conclude that the transformation has taken place in both dilatometers. 
(Comp. $ 6). 
9. These experiments consequently prove that potassium can 
undergo transformation into a second modification (3-Potassium) and 
that the metal as it has hitherto been known is at ordinary tempe- 
ratures a metastable system in consequence of the presence of both 
forms at the same time. 
10. The indications found in the earlier literature that this metal 
is able to crystallize as well in the regular as in the tetragonal 
systems *), gains more importance in the light of these results. 
141. R. W. and R. C. Duncan *) found that there existed a large 
difference between the indices of refraction of two mirrors which 
had been formed from molten potassium. Fresh experiments are 
wanted in order to decide whether these discrepancies are to be 
attributed to the presence of different quantities of the two modifi- 
cations in the mirrors experimented with. 
12. As the change of volume which accompanies the trans- 
formation mentioned, is considerable, it will be possible to investigate 
these phenomena by dilatometric measurements more closely than 
can be done at present from the data given by HaarN. We hope 
to report shortly on this point. 
Utrecht, January 1915. van ’r Horr-Laboratory. 
1) If the phenomena were to be ascribed to the melting process, the difference 
at 54°.25 C. at which temperature the metal is solid, would have been small (30 
units), which is really not the case. 
2) Apece’s Handbuch der anorg. Chemie 2, (1) 338—839 (Leipzig 1908) ; Lone. 
Journ. Chem. Soc. 18, 122 (1860). 
3) Phys. Rev. (2) 1, 294 (1918). 
