606 REPOiiT— 1901. 



described by earlier observers as ' crystalline.' This is not the case : it is spongy 

 or cellular, and appears under the microscope as if it had been suddenly cooled 

 ■while in a state of active effervescence. 



The penetration of the ammonia molecule into the metal is remarkably quick. 

 Iron and copper rods a quarter of an inch in diameter were completely penetrated 

 to the centre in thirty minutes. But disintegration goes on almost indefinitely 

 thereafter. Copper exposed for seven days to this action at a temperature of 

 80C° became reduced to a fine spongy powder. The prolonged action on platinum 

 produces very fine deposits of platinum black on the siu-face of the more massive 

 metal. 



The authors believe that the physical effects which result from this action are 

 explained by the alternate formation and dissociation of the nitrides of the metals 

 taking place between certain narrow limits of temperature, the reaction being 

 turned in either one direction or the other according as ammonia or hydrogen 

 molecules preponderate in the gases which are in contact with the molecules of 

 metal at and below the surface. 



It is suggested that the formation of spongy deposits on the outside of 

 platinum crucibles heated by Bunsen burners, as well as the disintegration of the 

 platinum wires of pyrometers exposed to furnace gases, may be accounted for by 

 the presence of traces of ammonia in the combustion gases. 



The absorption of small quantities of nitrogen by pure iron renders it hard 

 and brittle like steel. Malleable iron tubes exposed for seven days to the action 

 of ammonia at a temperature of 800° became so brittle that they could be broken 

 like porcelain by a blow from a hammer. 



It is suggested that some of the effects on the structure and properties of iron 

 and steel which are at present attributed to other elements may be due to the 

 presence of traces of nitrogen. 



6. Aluminium- Tin Alloys. By W. Cabrick Anderson, M.A., D.Sc, 



and George Lean, B.Sc. 



This investigation was undertaken to ascertain, with some definiteness, the general 

 properties of the alloys of aluminium and tin, and particularly the cause of the 

 peculiarity, first pointed out by Riche,^ that the alloy containing 26 per cent, 

 aluminium evolves hydrogen freely when placed in water. This property was 

 found to belong, not only to the particular alloy in question, but to the whole 

 series, whether cast or annealed. 



From the determinations of the cooling curves it is shown that tin dissolves in 

 aluminium, but that in the case of allovs containing more than 10 per cent, tin a 

 second break in the cooling curve takes place at 232° C., indicating an excess of tin.^ 

 Micro-photography was also employed to show the structure of the alloys in the cast 

 and annealed condition. The amounts of hydrogen evolved from the several alloys, 

 cast and annealed, were found to stand in no simple relation either to the weights 

 of the constituent metals present, or to the depression in the aluminium melting 

 point. 



From microscopic examination of water-corroded plates the conclusion is 

 arrived at that contact action between the tin and the stanniferous aluminium is 

 mainly responsible for this spontaneous oxidation. 



7. Aluminium-Antimony Alloys. By W. Campbell. 



8. Aluminiuin- Copper Alloys. By W. Campbell. 



' Riche, Jr. Pharm. Chem., 1895, I. v. 



" H. Gautier, Comptee Rendus, 123 [1896], p. 109. 



