Researches on Modern JExplosives. 



223 



that the indication of the galvanometer would show the rapidity with 

 which the temperature rose at the moment of the explosion, as well 

 as the rate at which the cooling took place. 



Through the kindness of Sir W. C. Eoberts-Austen we were enabled 

 to make some preliminary experiments in his laboratory, connecting 

 the wires from a couple in our bomb with the galvanometer in his 

 photographic-recording apparatus. The results of these experiments 

 were so encouraging that a similar photographic-recording apparatus 

 was procured, only introducing such slight modifications as were 

 required to make it more suitable for our purpose. 



We also had a special lid made for the calorimetric bomb previously 

 described in our former communication, this lid being similar to the 

 other, with the exception of two insulated conical pins, one made of 

 pure platinum and the other of platinum alloyed with 10 per cent, of 

 rhodium- These pins were used in the inside of the lid as points of 

 attachment for the thermo-couple, their ends outside the lid being con- 

 nected with the galvanometer. The couples were made of platinum 

 and rhodium-platinum wires in contact. Several couples of different 

 thicknesses were prepared for us by Johnson and Matthey, fusing the 

 ends of the platinum and rhodium-platinum wires together and then 

 drawing the junction through a die until it had the same diameter as the 

 rest of the wive. 



As we shall have to refer to these couples by number in future, 

 we give in Table I the diameters and areas, and the number by which 

 we distinguish each couple. As v/ill be seen, ten different couples 

 were made, the diameters varying from 0*044: to 0*01 of 1 inch : — 



Table 1. 



Couple Xo. 



Diameter in inclies. 



Area in sq. inclies, 



1 



0-044 



0-00152 







0-040 



0-00125 



3 



0-035 



0-00099 



4 



0-028 



0-00061 



5 



0-026 



0-00053 . 



6 



0-022 



0-00037 



7 



0-018 



0-00025 



8 



0-015 



0-00017 



9 



0-012 



0-00011 



10 



0-010 



0-00008 



Fig. 1 shows the explosive bomb with the lid separate, and the 

 arrangement of connections which are made through the lid are 

 clearly seen. Three insulated pins pass through the lid ; two of them, 

 as above indicated, are those which connect with the thermo-couple, 

 the other one is used as one of the terminals for the firing wire, the 



