CHEMISTRY. 517 



in a Hessian crucible with lime. The iridium melted by this process is 

 compact and crystalline ; it is harder than the natural metal, being 

 nearly as hard as the ruby; it has the color of steel and is not attacked 

 by acids. {Chem. ]!s^ews, xlv, p. 168.) 



Preparation and Properties of Metallic Cwsium. — Owing partly to the 

 extreme scarcity of material Biinsen's attempts to obtain ctesium in me- 

 tallic form were unsuccessful, but Carl Setterberg, availing himself of 

 the tons of alums obtained in Marquart's establishment as a secondary 

 product in the manufacture of lithium compounds from lepidolite, has 

 isolated this rare metal and studied its properties. Setterberg prepared 

 in 14 days 40 kilograms of rubidium alum and 10 kilograms of cassium. 

 He obtained metallic rubidium by decomposing the hydrogen-tartrate 

 with calcium carbonate and sugar, in a mercury flask, but attempts to 

 prepare caesium by a similar process were futile. By the electrolysis of 

 the cyanide of caesium mixed with barium cyanide in the ratio of 4 mole- 

 cules to one, Setterberg obtained the metal quite free from impurities. 

 Metallic caesium resembles closely the other alkali metals; is silver 

 white, malleable, and very soft at ordinary tern peratures. Thrown 

 upon water it floats around and decomposes it with evolution of heat and 

 light, in the same manner as potassium and rubidium. It inflames easily 

 when exposed to the air unless protected by a film of oxide or by a layer 

 of petroleum. The metal melts between 26^ C. and 21° C; its specific 

 gravity is 1.88 at 15° C. Examined in the spectroscope it showed only 

 traces of sodium as an impurity. 



Setterberg failed to detect new elementary substances in the residues 

 from which he extracted the rubidium and caesium salts. {lAebig's An- 

 nalen, ccxi, p. 100.) 



Nascent Hydrogen. — D. Tommasi, by numerous experiments on the 

 reducing power of nascent hydrogen, has been led to the conclusion 

 that its peculiar power varies with the reaction by which it is generated. 

 Hence, hydrogen in a nascent state may be regarded as hydrogen + 

 ealories; or H + «-, in which or has diSerent values according to the 

 source of the hydrogen ; thus : 



SO4H2 4- Zn + aq ; o' = 38 cal. 

 SO4H2 + Cd + aq ; a = 23.8 cal. 

 SO4H2 + Mg + aq ; «r = 112 cal. 



The hydrogen increases in activity with the increase in value of a j 

 for sodium amalgam it is 112 cal. {Bull. Soc. Chim., xxxviii, p. 150.) 



Preparation of pure Nitrogen. — Attempts to remove the last tr.aces of 

 oxygen from atmospheric air by means of phosphorus, potassium pyro- 

 gallate, hyposulphites, potassiumsodium alloy, and red-hot copper prov- 

 ing unavailing. Dr. Walter Flight found that it can be effected bypass- 

 ing the gas over a large surface of freshly precipitated ferrous hydrate. 

 The latter reagent he prepares by adding a strong solution of 80 grams 



