PHYSICAL CHEMISTRY 199 



bound. This view is supported by the tendency of these 

 metals to form complex anions in ammonia solution. 



The large number of compounds derivable from a given 

 pair of metallic elements has been an insurmountable obstacle 

 to the extension of the normal valency conceptions to inter- 

 metallic compounds. If, however, it be acknowledged that 

 metals tend to form complexes analogous to those of sulphur, 

 then this difficulty will disappear. The equivalent con- 

 ductivity of metallic compounds, their heats of formation, and 

 their mechanical properties are in agreement with the hypo- 

 thesis that these compounds are in effect salts. Their physical 

 properties are intermediate between those of pure metals and 

 salts. Thus metallic compounds are, as a rule, hard and 

 brittle. This resemblance between metallic compounds and salts 

 is the closer the more electropositive one constituent and the 

 more electronegative the other constituent of the metallic 

 compound. 



• The occurrence in the free state of radicals of the type 

 C3H7Hg possessing the properties of metals, throws light on 

 the source of the negative electron to which substances owe 

 their metallic properties. These electrons are evidently the 

 valence electrons. 



ORGANIC CHEMISTRY. By O. L. Brady, D.Sc, F.I.C, University 

 College, London. 



Photosynthesis of Nitrogen Compounds from Nitrates and Carbon 

 Dioxide. — In the January number of this journal an account 

 was given of the synthesis in vitro of formaldehyde and 

 carbohydrates from carbon dioxide and water under the 

 influence of visible light, thus imitating the first stage in 

 the synthesis of plant products. Baly, Heilbron, and Hudson 

 {Jour. Chem. Soc, 1922, 121, 1078) have now extended this 

 work to the study of the synthesis, under the influence at 

 present of ultra-violet light only, of complex nitrogenous 

 compounds. 



The original source of nitrogen for plant synthesis is either 

 nitrates or ammonia ; the present paper deals exclusively 

 with nitrates, but a further communication is promised in 

 which ammonia will be considered as a starting material. 

 The reduction of nitrates to nitrites is known to take place 

 in the plant, and Moore and Webster {Proc. Roy. Soc, 19 19, 

 [B], 90, 158) have shown that the same reaction takes place 

 under the influence of ultra-violet light. Baudisch {Ber., 191 1, 

 44, 1009) showed that when an aqueous solution of potassium 

 nitrite containing methyl alcohol was exposed to ultra-violet 

 light, formhydroxamic acid was produced (CH3OH + KNOg ->• 



