HEAT TREATMENT ON METALLIC SUSPENSIONS 35 
wire is then baked at 310°C for 2.5 hours. The temperature coefficient is then 
again measured between 20°C and 50°C and found to be —0.09 mm per °C. 
The process is then continued with successively higher baking temperatures. 
Fig. 2 shows that the temperature coefficient between 20° and 50°C becomes 
Q) 

Pt+ 107% Ir 
004mm 
50cm 

Fig 3. 
zero after baking at a certain critical temperature of about 425°C and takes 
on increasing positive values after baking at higher temperatures. Fig. 3 
shows similar and somewhat more consistent results obtained with another 
length of the same wire. The critical temperature is about the same in the 






| Material Tungsten 
Diameter O.O2mm 


Scale Dist 120m 




Fig. 4. 
two cases. Fig. 4 shows that for tungsten the critical temperature is consider- 
ably higher. These latter results are subject to considerable error because 
temperatures higher than 500°C were estimated roughly by the color of the 
hot wire. 
179 
