264 
MEASUREMENT OF HIGH TEMPERATURES. 
[BULL. 54 1 
Fig. 47a. Plan of helix and thermo-couples. 
These results (Tables 83 and 
84) justify the predictions inadi 
relative to the hurtful charactei 
of the leak. For if F{6") be con* 
structed it falls decidedly below 
the earlier curve. Below 1,000°, , 
moreover, the air and hydrogen 
loci show a striking degree oft 1 
coincidence (see chart, Fig. 48),, 
substantiating the earlier infer- 
ence that F (9") has the same 
value for these two gases, audi 
that the value of 6", thermo elecl 
trically measured, is not the true 
mean temperature at which trans} 
pi ration actually occurs^ Abovi 
1,000° the air and hydrogen! 
curves diverge; but this is due 
to the fact that platinum is much 
more pervious to hydrogen thaw 
to air. Again, in consequence of 
the tendency of the gases of the 
burner to enter the tubes, as well 
as the relatively large negative] 
errors of 0"at high temperatures, 
the curvature of both loci changes 
from cod cavity downwards be-; 
low 1,000° to concavity upwards! 
above 1 ,000°. Hence above 1 ,000° 
the true character of V'/ r /o is 
marred by the occurrence of dif- 
fusion across the walls of the 
platinum capillary tube. It ap- 
pears from the data, at extremes 
of high temperature (hydrogen; 
0=l,225o nearly, air 0= 1,335° ' 
nearly), that the large distortion 
produced by diffusion is never- 
theless of a determinable kind. 
It may therefore be eliminated 
by applying suitable corrections, 
as will be stated below. The oc- 
currence of the consecutive high- 
temperature points, lying nearly 
vertically one above another, is] 
due to the fact that the 11011- 
(918) 
