392 Scientific Intelligence. 



neutralization with ammonia presents some difficulty from the 

 fact that silver arsenate is soluble both in nitric acid and in 

 ammonia, a modification *of the process was proposed by Canby 

 consisting in neutralizing the solution with zinc oxide in place 

 of ammonia. This modification was criticized by Bennett, who 

 found it inexact, and proposed boiling with acetic acid in place 

 of nitric, neutralizing with sodium hydroxide solution in pres- 

 ence of phenolphthalein, and then making the liquid just acid 

 with acetic acid before precipitation with silver nitrate. 



Professor John Waddell, of Queen's College, Kingston, 

 Ontario, with the assistance of several students, has found that 

 the neutralization with considerable amounts of zinc oxide may 

 lead to very low, incorrect results, evidently from the formation 

 of zinc arsenate along with the silver arsenate, but he has found 

 that zinc oxide may be used for the neutralization with good 

 results if the acid has been previously almost neutralized so that 

 only a small amount of the oxide is employed after the addition 

 of silver nitrate. He has found, further, that the Bennett 

 modification may give somewhat high results, and he prefers to 

 boil the alkaline solution with nitric acid, to make slightly alka- 

 line with pure caustic soda, and then very slightly acid with 

 acetic acid before precipitating silver arsenate. — Jour. Indust. 

 and Engr. Chem., 11, 939. h. l. w. 



4. New Fluorescent Screens for Badioscopic Purposes. — Up 

 to the present time barium platinocyanide has been employed 

 for these screens, but recently their cost has become exorbitant 

 on account of the scarcity and high price of platinum. On 

 account of this inconvenience it has become very desirable to 

 replace the platinum compound with a cheaper substitute. P. 

 Roubertie and A. Nemirovsky have, therefore, introduced a 

 new compound for the purpose. As the result of a long search 

 by one of the authors it was found, as long ago as 1911, that the 

 tungstates of the magnesium group of metals become luminous 

 under the action of the X-rays. They have succeeded in prepar- 

 ing screens with these salts, especially with cadmium tungstate, 

 which gave very satisfactory results. These screens have certain 

 advantages. They are exempt from permanent phosphorescence 

 such as is displayed by certain sulphides which have also been 

 proposed for the purpose. They are unchanged by atmospheric 

 action and do not deteriorate under the action of the X-rays as 

 do the platinocyanide screens, and, further, unlike the latter 

 they give a white luminescence, with black shadows, agreeable to 

 the eye of the observer and also easily photographed. — Comptes 

 Bendus, 169, 233. h. l. w. 



5. Scattering of Light by Solids. — The earlier investigations 

 by R. J. Strutt on the scattering of light by gases and liquids 

 have been recently extended by the same author to substances in 

 the solid state. The materials studied were various kinds of 

 glass, different varieties of quartz, and Iceland spar. 



