1920 J 



on Low Temperature Studies 



281 



Several normally absorptive substances when sufficiently reduced 

 in thickness were found to behave like india-rubber and permit a 

 considerable transmission. The curves of Fi 



19 give some instances. 



PER CENT 

 ABSORBED 

 100 





® ROCK SALT, SILVER CHLORIDE a M0 BROMIDE 



(Ddecane (D glass 



(D ALCOHOL (D WATER 



©RUBBER © WHITE MICA 



(D BLACK MICA 

 Fig. 19. 



In the case of bodies crystalline at low T temperatures some of the 

 heat will be diffused, To estimate the possible error thus involved 

 several preparations were made of rock-salt, graded from polished 

 transparent plates to opaque blocks. The resulting values are shown 

 in the next table. 



Rock-Salt Tbansmissions. 



Bock«Salt, 1 mm. thick 



Plate, 2 polished surfaces 



,, 1 ,, and 1 rough surf ace 



,, 2 roughened surfaces 



Ground finely and compressed 



Ditto ditto after brine moistening 

 NaCl precipitated by alcohol ; \ 



dried and compressed/ 

 Ditto ditto, after brine moistening 



Heat 

 Transmission 



90% to 94% 



72% to 76% 

 62% to 64% 



70% 

 31% 



50% 



18% 



The comparison between polished rolled silver chloride and 

 bromide and a compressed plate of silver iodide is also interesting, 

 Vol. XXIII. (No. 114) u 



