530 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



leaf, but the moist vapour at once attacked it owing to the 

 liberation of mercury in the dissociation : 



Alexander Smith has recently shown (Zeit.physikal. Chem., 

 19.11, 76, 713) that calomel, heated at 115 C. during 5! 

 months in a sealed bulb containing phosphoric anhydride, 

 became so thoroughly dried that it would not vaporise at 

 all at 352 C. (usual vapour pressure 347 mm.). 



Baker's work on the oxides of nitrogen (1894-1912). 

 Baker found in 1894 (loc. tit. p. 613) that oxygen and nitric 

 oxide if carefully prepared and dried by phosphoric anhydride 

 during 10 days did not combine when mixed ; no con- 

 traction took place over mercury and no darkening of the 

 gas could be seen. But " when a small quantity of water 

 was introduced, dense brown fumes of the peroxide were 

 immediately produced." 



The dissociation of the gaseous peroxide, 



did not appear to be affected by drying the gas ; but later 

 experiments showed that the boiling-point of the liquid was 

 raised from + 22 to over + 69 C. by drying during more 

 than a year (Trans. Chem. Soc., 1912, 101, 2341). 



The trioxide, N 2 O 3 , or nitrous anhydride, forms blue 

 crystals melting at - 1 1 1 C., but dissociates completely when 

 vaporised at atmospheric temperatures : 



N 8 O 8 .- NO 2 + NO or 2 N 2 O 3 -> N 2 O 4 + 2NO. 

 The dried liquid, when evaporated, gave vapour-densities 

 ranging from 38*1 to 62*2 (hydrogen = i). As N 2 O 3 requires 

 V.D. 38 only, the vapour was not merely undissociated, but 

 actually associated, consisting largely of complex molecules, 

 e.g. N 4 O 6 , analogous to those present in the vapour of phos- 

 phorous anhydride, ~P 4 O 6 (Tnms. Chem. Soc., 1907,9!, 1862). 

 After 3 years' drying the boiling-point of the liquid was 

 raised from - 2 to + 43 C. : 



