836 



KEPORT — 1898. 



a radiograph about 3 per cent, deeper than the same quantity of the same class 

 ■when in the form of a polished plate. ParafEn gave the same amount of absorp- 

 tion whether it was solid or liquid. Pounded crystals of sulphate of copper and 

 ammonia gave practically the same absorption as a mere mixture of the two con- 

 stituent salts. Finely-divided metallic copper was found to absorb about 2 per 

 cent, more rays than the same amount of copper as black oxide or as red oxide. 

 That there was little or no effect produced by difference of atomicity was shown 

 by a comparison of these two oxides, and also of the two oxides of mercury, which 

 absorbed practically the same amount. The protoxide and peroxide of lead were 

 identical in their results ; and the ferric oxalate gave only 1 per cent, less absorp- 

 tion than the ferrous oxalate, plus as much oxalic acid as was ncjcessary to equalise 

 the carbon and oxygen in the two salts. 



The old experiment with carbon and various hydrocarbons was re-examined, 

 with a final result which may be expressed by the figures : — 



The experiments of this year confirm tbe opinion previously expressed that the 

 absorption of the llontgen rays by a compound body is dependent upon the absorp- 

 tion exercised by its constituents, little, if at all, modified by their physical condi- 

 tion, or by change of atomicity, or other difference of combination. 



The authors are disposed, however, to osk the question — whether the law may 

 not be more than proximately true ? There is superabundant evidence that the 

 Rontgen rays are not homogeneous. The slightly greater apparent absorption 

 produced by the pounded glass may be due to a little reflection or refraction from 

 the admixture of a small quantity of rays which, though they have passed through 

 aluminum foil, have properties somewhat analogous to ordinary light. The 

 slightly greater absorption caused by metallic copper and by black carbon may 

 also be due to the presence of such rays. 



They think it possible that if these rays could be entirely sifted away, Rontgen 

 rays would be obtained, which in their passage through a body would be affected 

 merely by the nature of the atoms forming it, and that the law that the absorption 

 by a compound is the mean of the absorptions due to its several constituents 

 would be not proximately but absolutely true. 



An apparatus was exhibited by which the ' grade ' of the Rontgen rays can b(^ 

 investigated quantitatively. 



5. Report on the Action of Light upon Dyed Colours. — See Reports, p. 285. 



On the Cooling Curves of Fatty Acids, 

 and E. H. Strange. 



By Dr. A. P. Laurie 



The melting-points of mixtures of fatty acids were determined by Heintz, and 

 the tables are quoted in the text-books. They show that the mixtures have a 

 lower melting-point than either of their constituents, thus showing a close analogy 

 to the behaviour of many alloys. We therefore determined to apply to these 

 bodies a method of investigation similar to that used by Professor Roberts Austen 

 in bis experiments on alloys. 



The melted fatty acids are placed in a test-tube surrounded by melting ice, and 

 a thermal junction connected to a mirror galvanometer inserted. The results 

 are photographed on a moving plate. The plate is calibrated by means of a 

 second thermal junction attached to a thermometer, and immersed in a large 



