Chemistry and Physics. 325 



are new, and have studied their solubility in and decomposition 

 by water. It was found that a large number of double chlorides, 

 bromides, and sulphates correspond to the type TJ0 2 X 2 ' # 2XX', 

 while the double nitrates, chromates, and fatty-acid salts belong- 

 to the type U0 2 X 2 '-XX', where X signifies an atom of a univalent 

 metal, and X' a valency of a negative atom or radical. There 

 are also exceptional types, such as U0 2 X 2 ''4XX'. 



T*he stability of the double salts with water was found by ana- 

 lyzing saturated solutions of them prepared at different tem- 

 peratures. When the ratios of the constituents in solution did 

 not agree with the composition of the original compound, decom- 

 position by water was shown. It was found that all the double 

 nitrates are thus decomposed at the lower temperatures experi- 

 mented with, while the double chlorides are more stable, and 

 those containing alkali-metals of higher atomic weights (Rb and 

 Cs), or complex radicals of strongly basic character, are not 

 decomposed at the observed temperatures. The alkali-metal 

 double sulphates are also stable, except when they form salts of 

 the type XJ0 2 X 2 /, 4XX / , which are extensively decomposed by 

 water. All of the salts decomposed by water were found to 

 become stable at higher temperatures, usually at about 60 or 80°. 

 — JBerichte, xxxvii, 461. h. l. w. 



3. The Presence of Formic Aldehyde in the Atmospheric Air. 

 — In the course of researches upon the atmospheric air, H. Henriei; 

 has detected the existence in it of a gaseous substance, other than 

 formic acid, possessing energetic reducing action, and capable of 

 reducing Fehling's solution and of decolorizing iodide of starch. 

 In order to study this compound and to determine its identity, he 

 examined rain-water which came from fogs. The samples of 

 water, after filtration, were concentrated slowly upon the water 

 bath from a volume of 30 or 40 1 to about 200 cc . The samples 

 were neutral at first, but became acid upon concentration, and 

 deposited a certain quantity of calcium sulphate' which was 

 removed by filtration. The products which were strongly col- 

 ored, with an orange-yellow tint, were subjected to simple distil- 

 lation, and the distillates contained formic acid and a reducing 

 agent which distilled in the presence of acids or alkalies, and 

 gave the general reactions for aldehydes as well as special reac- 

 tions for formic aldehyde. 



The author concludes that formic aldehyde exists in the air, 

 and that this substance, which is a powerful antiseptic, plays an 

 important role in connection with the purity of the air. — Comptes 

 JRendus, cxxxviii, 203. h. l. w. 



4. Revision of the Atomic Weight of Iron. — About four 

 years ago Richards and Baxter, by the reduction of ferric oxide 

 by hydrogen, obtained the value 55-883 (O = 16*000) for the 

 atomic weight under consideration. Baxter has recently made 

 further determinations of this atomic weight by comparison of 

 carefully purified and sublimed ferrous bromide with the silver 

 bromide produced by it, or, in other cases, the silver required to 



