8 Proceedings of the Royal Society of Edinburgh. [Sess. 
manometer, including the portion of B contained in the smaller furnace 
was found to be 130 c.c. 
The vapour density is therefore given by the equation : 
A _ / 0T030 K 1 99-21/0-06 P30\( T , 9 v 
t 2-016 x 63-73 ' p 63-73Vl073 + 853 ) ) " K> 
The barometer readings and the readings of the mercury manometer 
were reduced to 0° C. 
At the conclusion of the experiment the outside and inside of the bulb 
A (fig. 2), were both opened to the atmosphere. The zero point had not 
appreciably altered. 
The measured pressures and temperatures and the values of A calculated 
according to equation (2) are given in the table : 
Pressure 
in mm. 
Temperature 
in ° C. 
Yaponr Density, 
A. 
346-5 
437 
100-8 
383-5 
513 
100-6 
419-0 
593 
101-2 
466-0 
677 
99-5 
536-5 
823 
99-6 
556-5 
870 
99-9 
576-0 
912 
100-0 
Mean = 100*2 
The mean value of A is 1 per cent, higher than the theoretical value, 
99’21, calculated on the assumption that mercury vapour is monatomic. 
There is, however, a slight tendency towards a decrease at the higher 
temperatures, so that the discrepancy may be due to slight association. 
The apparatus was subsequently used by the author in conjunction 
with Professor A. Stock and Dr E. Stamm in an investigation on the 
dissociation of phosphorus vapour, the results of which are at present in 
course of publication. Highly accurate measurements were made up to 
1250° C. 
In conclusion, the author desires to thank Professor Stock for his kind 
permission to carry out this research in the Chemical Laboratory of the 
Technische Hochschule in Breslau, and to acknowledge with thanks the 
receipt of a grant for apparatus from the Carnegie Trust. 
{Issued separately January 17, 1913.) 
