310 F. J. Rogers — Magnesium as a Source of Light. 



radiation through an alum cell to the unobstructed radiation 

 and correcting for light absorbed and heat transmitted. 



IV. 



Seat of Combustion of Magnesium. 



In order to determine the total efficiency of magnesium light 

 it is necessary to know its heat of combustion. In determin- 

 ing this quantity a new form of colorimeter was used. In this 

 5. case the magnesium ribbon was 



burned in an entirely closed vessel 

 containing oxygen, not allowing 

 any of the products of combustion 

 to escape. Figure 5 represents a 

 vertical section of the calorimeter. 

 The smaller vessel, A, holds some- 

 thing over half a liter. This vessel 

 is provided with an air-tight cover 

 through which pass two electrodes 

 E, E ; , one of which is insulated 

 from the calorimeter. The outside 

 vessel is just large enough to allow 

 room between it and the inner 

 vessel for a stirrer, S, and a ther- 

 mometer T. 



The process was as follows : 

 About three fourths of a gram of 

 magnesium was coiled into a spiral 

 and a very small quantity of phos- 

 phorus fastened to it. The termi- 

 nals of the spiral were then con- 

 nected to the electrodes. Before 

 putting the magnesium into the 

 vessel, A, the latter was filled with 

 oxygen. After the inner vessel had 

 been closed, water was poured into 

 the calorimeter until it was a centimeter deep over the top of 

 the former vessel. The ribbon was then ignited by the instan- 

 taneous application of a current of electricity. This calori- 

 meter gave quite uniform results. In Table VI, are given 





Table VI. 







Lesser calories 





Lesser calories 



<To. 



per g. of Mg. 



No. 



per g. of Mg. 



1 



6246 



5 



6020 



2 



6081 



6 



6072 



3 



5760 



7 



6011 



4 



5878 



Average 



6010 



