1920-21.] Evaporation of Liquid Air in Vacuum Flasks. 105 
The last table shows that as 0 1 increased, the neck-loss rose to a 
maximum and then fell. The fall was due to the fact that the stream of 
cold air passing up the neck increased at a more rapid rate than did the 
passage of heat down the metal of the neck. 
By subtracting the ascertained neck-losses (Table IV) from the total 
losses (Table II) the . rates of evaporation (L) due to radiation plus con- 
duction across the vacuum were obtained (Table V) : — 
Table V. — Metal Flask : Losses due to Conduction plus Radiation across 
the Vacuum ; Neck-Losses Eliminated. 
Absolute Temperature, 
Outer Globe. 
d v 
Absolute Temperature, 
Inner Globe. 
0o- 
Radiation, plus Con- 
duction, grams per hour. 
L. 
283° 
82° 
3L5 
317° 
82° 
45*9 
343° 
82° 
56-8 
373° 
82° 
83-0 
With these values equation (3) takes the form : — 
L = 8 , 228(d 1 4 — (9 2 4 )10 ~ 9 + 0*00284(0! — 0 2 ) J^T~0 2 • • ( 5 ) 
Since, as before, the first term of the right-hand side of this equation 
determines radiation and the second term determines conduction, the 
complete analysis of the loss by evaporation is now possible. It is given 
in Table VI, the values for neck-conduction being copied from Table IV. 
The degree of agreement between the results derived from equation (5) 
and those obtained by experiment may be gathered by comparing the last 
columns of Tables II and VI. 
Table VI. — Metal Flask : Losses due to Conduction, Radiation and Neck, 
Severally Stated. 
Temperature, 
Outer Globe. 
Conduction 
across Vacuum, 
grams per hour. 
Radiation, 
grams per 
hour. 
Neck Conduction, 
grams per hour. 
Total Loss, 
grams per 
hour. 
10° C. 
10-9 
20-6 
11-0 
42 5 
15° 
11-3 
22T 
11-9 
45-3 
44° 
13*3 
32 5 
15-4 
61-2 
70° 
15-3 
44*5 
15-2 
75*0 
100° 
17-6 
62-4 
14-6 
94-6 
The radiation loss at ordinary external temperatures is thus, in this 
flask, about twice that due to conduction of heat across the vacuous space. 
