THOMPSON AND LOMBARD. — NITROGEN IN CALCIUM CYANAMIDE. 249 



the couple as was heated was also spoilt. It was therefore necessary to 

 give up the direct measurement by the thermo-couple and use a Wan- 

 ner optical pyrometer. The instrument used in this investigation had 

 just been calibrated by the Bureau of Standards, with results that were 

 not materially different from the calibration furnished by the makers. 

 The amyl acetate lamp was not sufficiently constant, however, and 



I* 8V ^ ef- 4% 6fi^^ — if 



HERAEUS ELECTRIC FURNACE 



no VObTS' (O AMPCReS 



Figure 2. 



therefore adjustment of the current in the small electric lamp of the 

 Wanner pyrometer was made as follows : A furnace, shown in Figure 

 2, was made by wrapping platinum foil one fourth inch wide and 0.001 

 inch thick about a Royal Meissen porcelain tube of 2.54 centimeters 

 inside diameter. A cylindrical piece of carbon was placed in the furnace, 

 and a small porcelain tube was passed through the larger one and through 

 a hole in the carbon. The smaller tube was to hold a thermo-electric 

 couple, the junction of which was in the same plane as one of the faces of 

 the carbon. The temperature of this face of the carbon was therefore 

 given directly by the thermo-electric couple. In order to adjust the 

 current in the Wanner pyrometer, the reading of the Wanner was set 

 to agree with that of the couple, a piece of glass cut from the same 

 plate as that closing the end of the tower of the vacuum furnace was 

 placed in the groove in the pyrometer provided for holding the smoked 



