Chemistry and Physics. 299 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. An Empirical Relation between Melting-point and Critical 

 Temperature. — F. W. Clarke calls attention to a remarkable 

 relation which appears to exist between the two constants under 

 consideration. The data are very meager, but the author has 

 been able to examine the ratio in the case of about thirty sub- 

 stances. 



In nine cases the absolute melting point is nearly, if not exactly 

 one-half the absolute critical temperature, that is, the thermo- 

 metric lengths for the solid and liquid states are equal. The 

 following table gives the data in these cases, where t is the melt- 

 ing-point, T the critical temperature, and the ratio that of the 



absolute temperatures, ^±1^:. 



t-\- 273 



t T 



degrees degrees. Ratio. 



Nitrogen _ —214-0 —146-0 2-18 



Carbonic oxide —207-0 —139-5 2-02 



Argon.. —1900 —121-0 1-83 



Methane —186-0 —82-0 2-19 



Hydrochloric acid —112-5 -f 52-0 2-02 



Hydrogen sulphide — 86*0 +100-0 2-00 



Ammonia — 75*0 +130-0 2-03 



Benzene... _ ± 3-0 +288-5 2-04 



Acetic acid + 17-5 +3220 2-05 



This simple relation, however, is not general, but there are 

 other marked regularities among related compounds. The fol- 

 lowing gaseous compounds of nitrogen give closely agreeing 

 results : 



t T 



degrees. degrees. Ratio. 



C,N, - — 34-5 +124-0 1-67 



N^O, — lO-O +171-0 1-64 



NO —167-8 — 93-5 1-70 



Np — 99-0 + 35-5 1-77 



Five aromatic bodies give : 



t T 



degrees. degrees. Ratio. 



0-Xylene —45-0 +358-0 2-77 



m-Xylene —53-0 -f 346*0 2-81 



C^H^Cl -40-0 +361-0 2-78 



C.H^Br —30-5 +397-0 2-75 



C,HT -28-5 +448-0 2-94 



