76 Scientific Intelligence. 



5. Heat of Formation and Stability of Lead and Silver Com- 

 pounds. — The impossibility of predicting from thermochemical 

 data the relative stabilit}^ of similar compounds of lead and silver 

 has been shown by Albert Colson. It might be supposed that 

 the carbonate and nitrate of lead would be more stable than the 

 corresponding silver salts from the following heats of formation : 



For PbC0 3 __ 166600 cal. 



For Ag a C0 3 120800 " 



Difference 45800 " 



For Pb(N0 3 ) 2 .._ 105400 cal. 



For Ag 2 (N0 3 ) 2 5 7400 " 



Difference.. 48000 " 



Now while lead carbonate shows the expected greater stability, 

 as it was found to give a vapor tension of one atmosphere at 

 285° in comparison with 220° for silver carbonate, the nitrates 

 show an opposite relative stability, as lead nitrate gave off red 

 vapors at 283° while silver nitrate was not decomposed even at 

 350° in a vacuum. The author has previously shown also that in 

 the general reactions of organic substances the results are not 

 necessarily governed by the maximum of disengaged heat. — 

 Gomptes Rendus, cxlviii, 837. h. l. w. 



6. Refraction of Rontgen Rays. — W. Wien and I. Stark 

 independently have shown that by the application of Planck's 

 radiation theory to Rontgen rays one obtains wave lengths which 

 agree closely with the values 5-16. 10 -9 cm. obtained by Haga and 

 Wind. In view of this B. Walter and R. Pohl have renewed 

 their work upon the subject of the refraction of the rays, and do 

 not find any evidence of this refraction. If" this does occur the 

 wavelengths must be less than l'2.10 _9 cm. ; a suitably small 

 bundle of the rays through a slit 2/x wide at a distance of 80 cm. 

 affords no evidence of refraction. Planck's wave length deduced 

 from the quantity of energy theory is at the lowest 4*5. 10 -9 cm. The 

 authors conclude, therefore, that there is a discrepancy between 

 this theory and their observations, still to be investigated. — Ann. 

 der Rhysik, No. 7, pp. 331-354. J. t. 



7. Polarization of Rontgen Rays. — In an investigation upon 

 this subject Haga has stated that the secondary rays are polar- 

 ized by a plate of carbon, and that these rays also are slightly 

 polarized by copper, aluminium and lead. He could not, however, 

 obtain any trace of polarization from the primary Rontgen rays. 

 J. Herweg is led to examine the primary rays proceeding from an 

 anti-cathode of carbon, and obtains evidence, in this case, of 

 polarization. He concludes that the rays from carbon differ in a 

 marked degree from those coming from metals. — Ann. der Rhysik, 

 No. 7, pp. 398-400. J. t. 



8. The Absorption of the y-Rays of Radium by Lead. — Various 

 observers have studied this subject, and have obtained exponen- 



