CAPACITY FOR HEAT OF METALS AT LOW TEMPERATURES. 
323 
previous work and, as the method is generally applicable to substances of low melting 
point, a brief description may be of use. 
A section of the block complete is shown in fig. 2. The heating element consisted 
of 300 cm. of double cotton covered manganin wire, No. 36, enclosed in a fine metal 
tube* of about I mm. bore; the total resistance of the coil was about 38 ohms. 
The wire was dipped in hot paraffin wax before insertion in the tubing and the 
insulation resistance between wire and tube was found to be entirely satisfactory. 
Fig. 2. A, tubing containing insulated manganin wire; B, hollow steel bolts brazed on to tubing to make 
joint with copper case; C, copper case silver-soldered at S; D, tube used for filling case with sodium, 
afterwards sealed off ; E, copper tube closed at lower end to contain Pt thermometer; F, copper leads 
to heating coil. 
The tubing was wound in the form of a double helix and spaced so as to be 
distributed as uniformly as possible through the volume of the sodium. 
(This would be a point of considerable importance when working with poor conductors 
of heat.) 
The other details of the construction will be understood from the figure. 
One further point, however, deserves mention, namely, the soldering on of the 
bottom of the case after the insertion of the helix. 
It was found that hard soldering was absolutely necessary and, since this involved 
* This solid drawn tubing was composed of copper alloyed with a small proportion of brass to 
strengthen it. 
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