412 A. L. Day and J. K. Clement — Gas Thermometer. 



coil upon it is then placed in position in the cylinder and the 

 remaining space between it and the cylinder wall filled with 

 magnesite cement of the same composition as the tube itself. 

 When this has set the arbor can be removed, leaving the coil 

 in position in the tube. It then remains merely to go over the 

 exposed wire with a very thin coating of the same cement and 

 the coil is ready for use. Such a coil is less liable to displace- 

 ment through expansion and contraction than when the wind- 

 ing is on the outside of the tube. We have had such coils in 

 constant use for a variety of purposes in the laboratory for 

 several years, and have found them durable, economical and 

 most convenient. 



In this particular furnace the windings are somewhat closer 

 at the top and bottom of the coil than at the middle, in order 

 to provide a more uniform temperature from one end to the 

 other. This scheme, although efficient and perfectly satis- 

 factory for most purposes, will not provide a perfectly uniform 

 distribution of temperature over long temperature ranges. 

 An arrangement of the turns which is adequate for low temper- 

 atures will not provide sufficient compensation at the ends for 

 much higher ones. We therefore prepared two secondary 

 coils of liner platinum wire in which the current could be 

 independently varied, and mounted them within the main coil 

 at the two ends of the tube. These coils extended into the tube 

 about 7 cm from each end and were fastened in position by smear- 

 ing with the magnesite cement as before. With this arrange- 

 ment, we are able to obtain a temperature distribution along the 

 bulb which did not vary more than 1° for all temperatures up 

 to 1200°. We have not yet attempted to go beyond this point. 

 To ascertain exactly what the temperature distribution was at 

 the moment of any pressure measurement, it was necessary to 

 use three thermoelements simultaneously, one principal element 

 at the middle of the bulb and secondary elements at each end. 

 These elements were carried out of the furnace between two 

 discs of rubber packing in the center of the cover. 



The bulb was symmetrically located in the center of this 

 furnace, the capillary stem extending out of the top of the 

 heating tube and then with a gentle bend of 90° passing out of 

 the metal bomb at the side of the cover, as can be seen in the 

 diagram (fig. 1). It was then connected by means of a second 

 smaller capillary of platinum with the top of the manometer 

 tube near the point of constant level adjustment. The iron 

 bomb thus prepared was water-jacketed around the sides and 

 at the top and bottom, which effectually prevented any of the 

 furnace heat from reaching the manometer which stood beside 

 it. The scale and mercury columns of the manometer therefore 

 suffered no exposure to temperature variation other than that 



