102 Proceedings of the Royal Society of Edinburgh. [Sess. 
the space between the inner and outer vessels with mercury vapour, and 
then exhausting. Some condensation of the residual vapour took place 
when liquid oxygen was introduced, causing the formation of a mercury 
mirror on the surface of the inner vessel. 
Table I. — Glass Flask : Evaporation Losses at Different External 
Temperatures. 
Temperature of 
Outer Vessel. 
Absolute 
Temperature of 
Outer Vessel. 
Absolute 
Temperature of 
Inner Vessel. 
6 . 2 - 
Evaporation, c.cs. 
of Gas per minute. 
L. 
-115° C. 
156° 
91° 
60 
- 78° C. 
195° 
91° 
120 
+ 6° C. 
279° 
91° 
300 
+ 65° C. 
338° 
91° 
600 
Neck-loss being inconsiderable, the total evaporation loss, L, is the sum 
of the losses due to radiation and conduction across the vacuum ; or, from 
equations (1) and (2): — 
L==Ct(0 1 4 — ^2 4 )'k^(^l — $ 2 ) T d 2 ■ * • (3) 
The values of the table are in reasonable agreement with the equation : — 
L = 3-O1(0 1 <-0 2 ^)]O- 8 +O-O41(0 1 -0 2 ) x /§H : 0 2 . • (4) 
The first term on the right-hand side of the equation expresses the loss 
due to radiation, and the second that due to conduction. At 15° C. radiation 
was responsible for the evaporation of 236 c.cs., and conduction across the 
vacuum for 138 c.cs. of gas per minute. Had the flask held liquid hydrogen 
instead of liquid oxygen, the losses at an external temperature of 15° C. 
would have been 238 c.cs. and 187 c.cs. per minute respectively. 
Estimation of the Three Causes of Evaporation Loss for 
a Small Metal Flask. 
The vessel is illustrated in fig. 2. It is a vaporiser flask, i.e. one whose 
function it is, by the aid of certain fittings, to evaporate liquid air at set 
rates. The fittings are not shown ; they were not attached during these 
tests. The capacity of the flask is 3 litres (about 7 lbs.) ; it is made of 
gilding metal (95 per cent, copper ; 5 per cent, tin), and the inner neck, C, 
is of cupronickel, an alloy having one-seventh the conductivity of copper. 
