88 Journal of the Mitchell Society [June 



gases passed over it. The heating was done by an electric sleeve and 

 the temperature up to 550° recorded by an accurate thermometer in- 

 serted in the tube with the bulb by the side of the boat. No cor- 

 rections were made for the portion of the thermometer stem exposed 

 beyond the tube, as such accuracy was not necessary. For tempera- 

 tures above 550° ammeter readings, which had been standardized, were 

 used. Two or three grams of the powdered samples were taken for 

 each experiment. 



Expt. 1. Litharge was heated quickly up to 300 -, then at the 

 rate of 5° to the minute. At about 345' it began to turn black and 

 at 360° it had changed entirely to black. At 390^ the color began to 

 lighten and at 400° it was pure white. No further change was ob- 

 served up to 550". The white powder (lead chloride) was entirely 

 dissolved by water. This experiment is especially instructive as the 

 two steps in the reaction, first a reduction followed by chlorination, 

 are quite distinct. 



Expt. 2. The green oxide of uranium (UoOs) was treated in the 

 same way and also showed the antecedent reduction changing at first 

 into the black oxide (U3O5) at 450° and forming the chloride at 500^. 



In the remaining experiments the two steps, reduction and chlori- 

 nation, if they occurred separately could not be distinguished. Chromic 

 oxide began to chlorinate at 625°, stannic oxide at 400°, alumina at 

 450°, manganese dioxide at 460°, calcium oxide at 630°, magnesia at 

 475°, ferric oxide at 460° and zirconia at 480°. 



The mixture of gases used in these experiments probabl}^ contained 

 an excess of carbon monoxide. For a few of the substances the re- 

 action was repeated with a considerable excess of chlorine. Under 

 these conditions the chlorination temperature for ferric oxide was 

 lowered from 460° to 370° and for zirconia from 480° to 425°. 



A comparative table of the approximate chlorination temperatures 

 follows : 



CO + CI, COCl, -1- Cln 



480= 425° 



400° 



47.5° 



450° 



