TKANSACTIONS OF SECTION B. G39 



If the metallic mirror be gently heated by waving the Bunsen flame over it in 

 a current of hydrogen, it evaporates, and again deposits as a black powder. In 

 this form it is not so easily compared with other deposits as the brown metallic 

 form. These deposits, and more especially those in the form of black powder, fade 

 v?hen exposed to the light. The fading is most marked when the deposits are 

 exposed in atmospheres of oxygen or nitrogen, and least in hydrogen and carbon 

 dioxide. 



The process as described (after destroying all organic matter with nitric and 

 sulphuric acids) will show a distinct mirror with ^uVxt o^ ^ grain per gallon, and 

 the half of this can be distinctly detected. 



The Marsh-Berzelius test is much more delicate than the electrolytic method 

 recently devised by the Select Committee appointed by the Government. The 

 platinum kathode will not give a mirror with a smaller amount than ^^^ of a 

 grain per gallon when working on 50 c.cs. of liquid ; if a pure zinc kathode be 

 used much greater delicacy can be attained, but even this is not equal in delicacy 

 to the ordinary Marsh-Berzelius process. 



8. Report of the Committee on the Study of Hydro-AromMtic Substances. 



See Reports, p. 179. 



Report of the Coinmittee on Wave-length Tables of the Sjyectra of the 

 Elements and Comjwunds. — See Reports, p. 87. 



10. Ex2)eriments and Observations with Radium Compounds, 

 By "William Ackroyd, F.I.C. 



The telluric distribution figure for radium is "OOOS when gold = 1.^ The 

 effects produced by rays from radium compounds simulate those of sensible heat 

 in a very remarkable manner. 



Phosphorescence. — ^Attention was early paid to diathermanous common salt, 

 NaCl, under the influence of radium rays. This body was found to become in a 

 few hours remarkably phosphorescent, and the phosphorescence lasts for hours 

 after the removal of the exciting cause.- Slides of the photographic results are 

 shown of— 



1. A radium bromide tiibe alone containing 5 milligrams of the pure sub- 

 stance. Exposure, two minutes. 



2. A radium bromide tube plus the sodium chloride in which it is imbedded. 

 Exposure, two minutes. 



3. Sodium chloride alone after action of radium rays. Exposure, thirty 

 minutes. 



The table salt experimented with was of slightly alkaline reaction to red 

 litmus with traces of the usual impurities. The compound was therefore prepared 

 (1) by precipitation from its solution with hydrochloric acid gas and (2) by the 

 neutralisation of caustic soda solution with hydrochloric acid. In each case the 

 sodium chloride became phosphorescent under the radium rays. The chloride 

 with a trace of moisture in it gave better results than salt kept carefully dry in 

 a desiccator after ignition. Salt moistened with hydrochloric acid solution, a 

 little over normal strength, also exhibited phosphorescence. 



Phipson in his ' Phosphorescence,' p. 20, says common salt is phosphorescent 

 only at a temperature of about 200° C, and Sir D. Brewster observed phospho- 

 rescence when a solution of common salt was poured into a cup of heated iron.^ 



« B.A. Jicjwrt, 1902, p. 581. - Miture, July 23, 1903. 



' Black'm's Pop. Ency, xi. p. 49. 



