67 
Ordinary Meeting, January 27th, 1874 
B. Angus Smith, Ph.D., F.RS., &c., Vice-President, in the 
Chair. 
Mr. John Watts, Ph.D., was elected an Ordinary Member 
of the Society. 
On a Source of Error in Mercurial Thermometers,” by 
Thomas M. Morgan, Student in the Laboratory of Owens 
College. 
While engaged in distillation, a fact has come under my 
observation which, although it has been noticed before, does 
not appear to be very generally known, and has not so far 
as I have seen been recorded. 
The thermometer, which was placed in a Wurtz tube so 
that the column of mercury was entirely surrounded by the 
vapour of the distilling liquid, was found after some days 
to indicate three degrees too little — a discrepancy caused by 
volatilization from the surface of the column of mercury and 
condensation on the upper part of the tube. By causing 
the mercury to how to the end of the tube and back, the 
condensed portion was gathered up and the correct tem- 
perature indicated. It has since been observed that after 
each day of distillation, with liquids boiling between 60° 
and 100° Q, a quantity of mercury equal to 1° or 1°'5 vola- 
tilizes, and that this quantity is scarcely perceptible when 
condensed on the surface of the bore. The thermometer in 
use was about the ordinary size with a scale of 360°. 
1 am informed that Geissler sometimes encloses a little 
hydrogen in his thermometers in order that volatilization 
may not go on so rapidly. 
Peocbedings. — Lit. & Phil. Society. — Yol. XIII. — No. 7 — Session 1873-4. 
