BARUS.] 
PYRO-ELECTRIC PROPERTIES OF ALLOYS. 139 
Table 28. — Thermo-electrics of platinum alloys— Continued. 
No. 
t 
T 
e 
observed. 
e 
calculated. 
103 x a 
10 6 X& 
f-47+0 
18 
100 
— 39 
— 39 
— 443 
— 274 
Bi .. 
...J -47+0 
22 
358 
— 188 
— 184 
l_47+0 
19 
448 
— 245 
— 245 
p + 52—0 
19 
100 
+ 18 
+ 18 
+ 612 
— 3288 
—52+0 
24 
858 
— 248 
— 215 
Zn.. 
,... 
—52+0 
+54-0 
19 
19 
448 
100 
— 396 
+ 19 
— 39G 
+ 19 
+ 296 
— 514 
+54—0 
24 
358 
+ 18 
+ 33 
, +54—0 
19 
448 
+ 24 
+ 24 
Temperature-coefficient. — Table 33 contains the final series of data rel- 
ative to the pyrometric constants of these wires. It contains mean 
values of the relation a between electrical resistance and temperature 
for each of the 52 wires of the above table. The marked ends of these, 
having been wrapped around the little insulating cylinders of porcelain 
so as to form a helix, the platinum spires of which do not touch each 
other ("open spiral spring"), were exposed to 25°, to 100°, and to 358°, 
respectively, in the space of constant temperature of my boiling tubes. 
To retain the helix, which is never more than 2 cm long along its axis, in 
place, and likewise to connect the terminals of the bridge adjustment 
with it, the ends of the helix wire are fused to terminals of fairly-thick 
copper wire. One of these terminals passes through one canal of the 
porcelain insulator to connect with the upper end of the platinum helix, 
the other terminal partially through the second canal in a suitable way 
to connect with the lower end of the helix. The measurements are 
then made in the customary way. Constancy of temperature along the 
2 cm of length of helix may be assumed. The total length of platinum 
wire in the helix is that for which the above data, Table 31, apply. 
In Table 33 therefore r t is the resistance corresponding to the tem- 
perature T, and <V 00 , #o 360 are the -mean temperature-coefficients for the 
intervals of temperature 0° to 100° and 0° to 360°, respectively. 
Table 33. — Temperature-coefficients of platinum alloys. 
No. 
T 
rt 
10 3 x a 100 
lO^xa^o 350 
[ 

25 
0.759 
2.30 
2.22 
-! 


100 
357 
0.883 
1.296 
r 
1 
1 
1 
20 
100 
357 
0.408 
0.464 
0. 630 
1.78 
1.62 
2 
21 
0. 485 
1.45 
1.33 
Au..<; 
2 
2 
100 
357 
0.539 
0.702 
3 
22 
0. 542 
1.27 
1.09 
3 
100 
0. 594 
3 
357 
0.744 
(793) 
