1898.] 



on Liquid Air as an Analytic Agent. 



827 



Photographic Action at the Temperature of Liquid Air. 



In a former lecture on Phosphorescence and Photographic Action, 

 it was shown that photographic action was reduced by 80 per cent, 

 at the temperature of — 182° C. It was further proved that a sensi- 

 tive film was still comparatively active at the temperature of — 210° C. 

 Experiments in this direction have been continued at different times. 



In these new experiments the source of light was respectively a 16 

 candle-power lamp, a magnesium and cadmium spark discharge, and 

 a Eontgen bulb. Small dark slides were prepared having a circular 

 hole. One was placed in liquid air, and another simultaneously exposed 

 for the same time at the ordinary temperature (Fig. 7). They were 

 developed together, and the density of the image observed (Fig. 5). 



• e 



Fig. 5. 



1, photographic film exposed at ordinary temperature. 2, photographic film 

 cooled in liquid air during exposure. 



Both were exposed for the same length of time, and both were developed 

 together. 



2. 



Fig. 6. — Ultra-violet spectrum of spark discharge. 



1, on film at ordinary temperature. 2, on film cooled in liquid air. 

 Both exposed for the same length of time and then developed together. 



