CAPACITY FOR HEAT OF METALS AT LOW TEMPERATURES. 321 
After expansion the air circulated through the coil of lead tubing, D, and then 
back over the surface of the interchanger coils. 
A 
Fig. 1. BB, interchanger coils; C, valve; D, coil piping around enclosure ; E, thick copper enclosure ; 
F, insulated copper wire around enclosure ; G, metal block ; H, supporting tube; K, taper plug 
closing central hole in block; 0, heating coil; T, platinum thermometer; N, cardboard tube to 
keep slag wool in position. 
On the exterior surface of the thick walled copper enclosure, E, was wound a layer 
of insulated copper wire, F, which served as a resistance thermometer. Variations in 
2 T 
VOL. CCXIV.-A. 
