CHEMISTRY. 649 



exclusively are iu reality due to liglit and heat, or to the latter agent 

 only. The decomposition of liquid phosphine is generally attributed 

 to light, but the author shows that it can be exposed to direct sunlight 

 at 10° without a trace of decomposition. Heat alone without light is 

 inactive. 



A mixture of chlorine and hydrogen can be exposed with impunity 

 to sunlight if cooled to— 120C.; a temperature of 29° is not able to 

 eftect combination of the gases without sunlight. Chloride of silver 

 requires both heat and light for its decomposition, and Fehling's solu- 

 tion is not changed by light alone; if organic dust be excluded the 

 solution will keep indefinitelj^ when exposed to full sunlight. {Gazetta 

 chimica italiana, xiv, 57.) 



INORGANIC. 



Manufacture of Oxygen and of Ammonia from the Atmosphere. — The 

 well-known process of extracting oxygen from the atmosphere by 

 means of baryta has never been a commercial success, because after 

 a while the baryta becomes inactive, owing probably to its absorption 

 of carbonic acid from the air. At the " Inventions Exhibition," held 

 during the summer months in London, the brothers Briu exhibited an 

 improvement on the old process which promises to be very valuable. 

 Tlie air is freed from carbonic acid and water by caustic soda and then 

 passed over barium oxide, heated to a temjierature not above 000° C, 

 in iron retorts. The temperature is regulated by a pyrometer, which 

 controls also the supply of gas to the furnace. Under these conditions 

 the oxygen of the air is absorbed by the baryta, barium peroxide being 

 formed. The nitrogen which appears to be very pure is collected 

 separately for use iu the production of ammonia. On heating the 

 peroxide of barium to full redness pure oxygen is given off. At this 

 stage of the process powerful pumi)s are set in operation and make a 

 partial vacuum in the retorts. The operations are continuous, and so 

 long as the baryta is kept anhydrous and free from carbonic acid the 

 same quantity will apparently last an indefinite time. The most inter- 

 esting and perhaps the most useful part of the invention of the Briu 

 Brothers is the production of ammonia by a very direct process. The 

 nitrogen obtained as above and moisteiie<l by passing through water, 

 is passed over a mixture of baryta, with charcoal heated to about 300° 

 C. Carbonate of ammonia is thus obtained, the water being decom- 

 posed under the conditions named, its hydrogen combining with the 

 nitrogen and its oxygen vvith the carbon. The ammonium compound is 

 formed in considerable amount. {Nature, xxxii, 354.) 



Solid Nitrogen^ Lotcest Known Temperatures. — K. Olszewski in a 

 previous memoir describes apparatus for obtaining very low tempera- 

 tures by means of oxygen and of air evai)orating in a vacuum. In a 

 subsequent series of exi)eriments the author has further introduced into 



