316 Scientific Intelligence, 



metallic zinc, and after oxidation with potassium permanganate 

 and the removal of chlorine by boiling, the iron can be deter- 

 mined by the stannous chloride titration. Weil now calls atten- 

 tion to an improvement in his process by which the disagreeable 

 vapors of boiling hydrochloric acid may be dispensed with. He 

 adds to 10 cc of the liquid to be analyzed 30 cc of hydrochloric acid 

 and some pieces of white marble in a flask, and then runs in 

 stannous chloride at the ordinary temperature. The carbon 

 dioxide fills the flask and keeps out the air. — Comptes Rendus y 

 cxxxiv, 115. h. l. w. 



3. Comparison of the Properties of Hydrogen Selenide loith 

 those of Hydrogen Sulphide. — A careful study of the physical 

 properties of hydrogen selenide has been made by de Forcand 

 and Fonzes-Diacon. Several constants relating to hydrogen 

 sulphide which were previously somewhat doubtful have also 

 been determined in order that a comparison could be made. The 

 results are given in the following table : 



H2S • H^Se 



T, boiling-point (abs.) 211-4° 231° 



T c , critical temperature (abs.) 373*2 410 



T 



^ _ -566 -564 



■A c 



P c , critical pressure, atmospheres 92- 91* 



T', melting-point (abs.) 187* 209 



D, density of liquid at T -86 2*12 



PM 



-=— , molecular volume of liqnid _ 39-53 38-11 



L, heat of volatilization (calories) .__ 4230 4740 



^ Trouton's relation 20-01 20*52 



C, heat of formation of hydrate (calories) 16340 16820 



t, temperature at which the hydrate has a ) QHQ „_ OQ1 



tensionof 760 mm (abs.) J j/ ^ 5 ZbL ' 



S, solubility at + 4° (volumes) 4*04 3-77 



" -f 9-65 " 3-60 3-43 



" +13-2 " _ 3-35 3*31 



" +22-5 " _ 2*75 ' 2*70 



It is evident that the two gases show a remarkable analogy, 

 but their properties are very different from those of water, as is 

 shown by the following relations of the latter : 



PM L T 



^-= 18-82, -== 25-87, =- = -585, P c == 200 atm. 

 ±J X J. c 



— Comptes Rendus, cxxxiv, 281. h. l. w. 



4. Radio-active Thorium. — Hofmann and Zerban have found 

 that thorium preparations from broggerite, while showing much 

 activity in acting upon the photographic plate and upon the 

 electroscope when freshly prepared, lose this power almost or 



