Chemistry and Physics. 347 



salt (CH 3 NH 2 )AuBr 4 , the tetra-ethyl ammonium salt (C 2 H B ) 4 N- 

 AuBr , etc. The authors have decided from their experience 

 with a large number of salts that the double gold bromides of the 

 organic bases are not well suited for the examination of such 

 bases on account of their usual difficult crystallization and their 

 frequent instability. — Zeitschr. anorgan. (J hem., lxxxvi, 353. 



h. l. w. 



4. The Gravimetric Determination of Selenium. — Julius 

 Meyer has shown that the evaporation of nitric acid solutions of 

 selenious acid leads to the loss of appreciable amounts of the sub- 

 stance, and that the loss may be serious when the dry residue is 

 heated for a long time on the water bath. Although several of 

 the best authorities recommend the removal of nitric acid in the 

 course of analysis by repeated evaporation with strong hydro- 

 chloric acid, Meyer has found that this operation leads to very 

 serious losses even in the presence of potassium or sodium chlor- 

 ide. For instance, nearly one-half of 0-14 g. of selenium was lost 

 by evaporating its nitric acid solution to dryness twice with con- 

 centrated hydrochloric acid. The author recommends the em- 

 ployment of hydrazine hydrate for the precipitation of selenium, 

 and he states that the interfering effect of nitric acid may be 

 overcome by the addition of ammonia and some hydrochloric 

 acid. — Zeitschr. analyt. Chem., liii, 145. h. l. w. 



5. Active Nitrogen. — E. Tiede and E. Domcke maintain that 

 Strutt's phenomena attributed to active nitrogen, which are pro- 

 duced by passing electric sparks through nitrogen at low pres- 

 sures, do not occur when pure nitrogen is employed, and that 

 they are due to the presence of oxygen in the gas used. When 

 they used pure nitrogen prepared by heating barium or sodium 

 azide no luminescence occurred. By the use of hot metallic cop- 

 per they were able to purify commercial nitrogen so that the 

 after-glow did not occur, but they showed that the addition of 

 oxygen to the gas brought about its appearance. The curious 

 fact was brought out that metallic copper will remove the oxygen 

 from its mixture with nitrogen at temperatures between 325° C. 

 and 570° C, but that when the temperature is between 570° C. 

 and 700° C. some oxygen remains in the gas, evidently on account 

 of the dissociation of copper oxide at the low pressures (2 to 

 12 mm ) employed. — Berichte, xlvii, 420. h. l. w. 



6. Hays of Positive Electricity and their Application to Chem- 

 ical Analyses ; by Sir J. J. Thomson. Pp. vii, 132, 50 figures 

 and 5 plates. London, 1913 (Longmans, Green and Co.). — This 

 book will doubtless be received with enthusiasm by most ph} r si- 

 cists because it gives a consecutive account of the brilliant series 

 of researches on positive rays carried out during the past seven 

 years in the Cavendish Laboratory. Some idea of the scope of 

 the work may be formed from the following list of headings of 

 the sub-divisions of the text. (The material is not arranged in 

 numbered chapters.) "Rays of Positive Electricity. Double 

 Cathodes. Rectilinear Propagation of the Positive Rays. Elec- 



