Chemistry and Physics. 143 



mal value becomes practically zero at loo above this boiling 

 point, chlorine reaching its normal density at 240 c above its 

 boiling point, and iodine at its boiling point. .Tahn attributes 

 this to molecular aggregation, the molecules becoming single and 

 separate only at temperatures at which the vapor-density becomes 

 normal. — Bar. Berl. Chem. Ges., xv, 1238, June, 1882. g. f. b. 



•'I. Xffir f/ii-f/ni'/ /•>,• /•,'! fturi'ii'/ U'ji-oit'itronx acid. — For the pro- 

 duction of hy] iti'ous acid, UNO, the agents hitherto used for 



the redin.-tion of the nitraie or nitrite have been sodium-amalgam 

 or electrolysis, mercury being the negative elect rode. Zokn has 



eonelnsion that the best reducing agent for this purpose is fer- 

 rous hydrate. When freshly precipitated ferrous hydrate is 

 placed in a solution of sodium nitrate or nitrite, it reduces it 

 energetically, evolving heat and becoming ferric hydrate. Their 

 results hyponitrous oxide, hyponitrous acid, ammonia and nitro- 

 gen. In practice, pure ferrous sulphate is dissolved in water and 

 mixed with milk of lime, avoiding an excess, and leaving the 

 solution slightlv acid. To this thin magma is added, a solution 

 of sodium nitrite (one part of the nitrite being used for every 10 

 parts of the ferrous sulphate) and the whole is well cooled. The 

 "ias> foams, and the reduction is effected in a few hours. It is 

 strained and filtered, carefully neutralized with acetic acid, and 

 precipitated with silver nitrate. The precipitate of silver hypo- 

 nitrite is perfect lv pure since by this method of reduction no 

 "vdroxylamine is" formed, and 'therefore no metallic silver is 

 mixed with the precipitated hyp.mit.rite. From 100 grams 

 nitrite ami o,,e kilometer of ferroii.- >ulphate, 1 o -rams pure sil- 

 ver hyp., nitrite was obtained.— II,-?. IhrL </„,„. <i,«., xv, 1258, 



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