368 Prof. Boherfs- Austen [May 11, 



Special attention was then devoted to tlie work of Joule and Lyon 

 Playfair, who showed, in 1846, that metals in different allotropic 

 states possessed different atomic volumes, and the lecturer then pro- 

 ceeded to the consideration of the work of Matthiessen who, in 1860, 

 was led to the view that in certain cases when metals were alloyed, 

 they passed into allotropic states, probahly the most important 

 generalisation which has as yet been made in connection with the 

 molecular constitution of alloys. 



Instances of allotropy in pure metals were then shown to the 

 audience, such, for example, as Bolley's lead which oxidises readily 

 in air ; Schlitzenberger's coi>per ; Fritsche's tin, which fell to powder 

 when exposed to an exceptionally cold winter ; Gore's antimony ; 

 Graham's palladium ; and allotropic nickel. It was further shown 

 that metals could be obtained in chemically active states under the 

 following conditions ; — Joule proved that when iron is released from 

 its amalgam by distilling away the mercury the metallic iron takes 

 fire on exposure to air, and is therefore clearly different from ordinary 

 iron, and is, in fact, an allotropic form of iron. Moissan * has shown 

 that similar effects are produced in the case of chromium and man- 

 ganese, cobalt, and nickel, when released from their amalgams with 

 mercury. 



Evidence is not wanting of allotroj^y in metals released from solid 

 alloys, as well as from fluid amalgams with mercury. Certain alloys 

 may be viewed as solidified solutions, and when such bodies are 

 treated with a suitable solvent, usually an acid, it often happens that 

 one constituent metal is dissolved, and the other released in an in- 

 soluble form. Eeference was then made to a new alloy of potassium 

 and gold, containing about ten per cent, of the precious metal. If a 

 fragment of this alloy be thrown upon w\ater, the potassium takes fire, 

 decomposes the water, and the gold is released as a black powder ; 

 there is a form of this black or dark-brown gold which aj^pears to 

 be an allotropic modification of gold, as it combines with water to 

 form auric hydride. By heating this dark gold to dull redness, it 

 readily assumes the ordinary golden colour. The Japanese use this 

 gold, released from gold-copper alloys, in a remarkable way, for they 

 produce, by the aid of certain pickling solutions, a beautiful patina 

 on copi^er which contains only two per cent, of gold, while even a 

 trace of the latter metal is sufficient to alter the tint of the patina. 



With regard to theoretical views as to molecular change in metals, 

 special care was given to a description of the work of Professor W. 

 Spring, of Liege, who had furnished much evidence in support of the 

 view that polymerization of metals, that is the rearrangement of atoms 

 in their molecules, could take place even in solid alloys of lead and tin. 



With reference to the passage of metals into allotropic states 

 under slight external influences, it was stated that Debray t has 



* Comptes Rendus, vol. Ixxxviii. p. 180, 1879. 

 t Ibid. vol. xc. p. 1195, 1880. 



