Chemistry and Physics. 575 



process verified the electrical method and, when this was not the 

 case, the author gives a valid explanation of the divergence, the 

 photographic method being subject to secondary influences which 

 were eliminated in the electrical experiments. 



In substance, Friedrich summarizes his results as follows : 

 1. The intensity of X-rays, which come from a platinum anti- 

 cathode and which pass through a uniform thickness of 2 mm of 

 compensated glass wall, shows a dependence upon the azimuth, 

 when investigated either by the photographic or by the electric 

 method. 2. The maximum of intensity does not lie at right 

 angles to the direction of the cathode ray beam, but is displaced 

 towards the side of the azimuths less than 90°. The harder the 

 X-rays, the greater is this displacement. 3. The determination 

 of the distribution of intensity by the electrical method gives, on 

 the average, a difference of intensity of 20 per cent between the 

 azimuths 80° and 150°. 4. The hardness of the X-rays is like- 

 wise a function of the azimuth. It increases, for the directions 

 studied, with decreasing azimuth. 5. At the azimuth 0° a mini- 

 mum of intensity of X-rays which had come from a platinum 

 anticathode and which had passed through a sheet of aluminium 

 0-01 mm thick, was established photographically.— Ann. d. Phys., 

 No. 12, September, 1912, p. 377. h. s. v. 



8. Experimentelle Bestimmung des VerJiMlnisses der spezi- 

 fischen Wdrmen c p'/c v bei Kalium — una Natriumddinpfen and 

 daraus sich ergeben.de Schlussfolgerungen. — As is well known, 

 lithium^ potassium, and sodium obey the law of Dulong and Petit. 

 Furthermore, vapor density determinations have led to the conclu- 

 sion that the vapors of cadmium, lead, merciuy, silver, thallium, and 

 zinc are monatomic. These, and other facts, have led F. Richarz 

 to advance the hypothesis that, in general, metallic vapors con- 

 sist of monatomic molecules. By improving the apjjaratus used 

 by his predecessors, Max Robitzsch has verified this hypothesis 

 for the vapors of potassium and sodium. 



A steel tube about 7o cms long and 2 - 8 cms internal diameter was 

 placed inside an electric furnace. This tube was provided with 

 a steel piston which enabled the experimenter to vary at will the 

 length of the column of vapor inside the tube. The other end of 

 the tube was closed by a thin membrane of mica. The chief 

 improvement in the apparatus consisted in placing an adjustable 

 resonance tube between the mica membrane and the exciting 

 pitch pipe. When both the resonator and the pitch pipe were 

 carefully tuned to one of the natural periods of vibration of the 

 membrane, very definite maxima of sound intensity could be 

 observed when the steel piston occupied the proper positions one- 

 half of a wave-length apart. The steel tube was filled with the 

 indifferent gas nitrogen before the introduction of the metal to 

 be vaporized. 



For potassium vapor having a temperature between 950° C. and 

 1000° C. the ratio y of the specific heat at constant pressure to that 

 at constant volume was found experimentally to be 1*64. From 



