TRANSACTIONS OF SECTION B. COo 



These two forms of ' metal substance ' occur in all of the metals examined, anJ 

 taken together they do not appear to depend in any way on the particular thermal 

 or mechanical treatment to which the metal has been subjected, nor on the greater 

 or less mass of the particular piece of metal examined. Their existence is 

 therefore to a great extent independent of the conditions which determine the 

 particular crystalline structure of metals and alloys. 



In form "(a) the granules or scales do not vary much in size in the different 

 metals examined, which include among their number representatives of most of 

 the great groups. The diameter of the scales is estimated to range from g^j^ to 

 j^^ of a millimetre. Their thickness has not yet been measured, but they can_ be 

 seen by reflected light when their thickness is certainly less than j^^xj^ o^ ^ milli- 

 metre. 



Form (6) is seen as a transparent glass-like film on metal surfaces, which have 

 been exposed to certain forms of pressure. In the transparent form the metals 

 Lave their characteristic colours by transmitted light ; for instance, gold is green, 

 iron and platinum are blue, copper is i-ed, nickel is olive green. 



The scale form (a) passes into the transparent form (h) when the metal is pressed 

 or hammered upon a hard polished surface. The same effect takes ])lace when a 

 miiTor-like polish is produced by ordinary methods. Files or cutting tools in 

 passing over the surface or through the substance of metals leave the cut or 

 scraped surface covered with a more or less continuous film of transparent metal. 

 By suitable treatment a coating of transparent metal can be formed of varying 

 degrees of thickness, so that by rejected light .«cales can be seen more or less deeply 

 imbedded in the transparent coating. The light from the deeper scales shows the 

 characteristic colour of the metal. In .some cases the colour of the coating 

 appears so dense — as seen by the microscope — that no reflected light reaches the 

 surface. 



Attempts have been made to measure the thickness of the transparent film by 

 focussing for its upper and lower surfaces, or for the upper surface, and for scales 

 embedded in the film, and measuring the movement of the microscope between 

 the two points. As these measurements appear to give rather exaggerated results 

 their publication is held over for the meantime. 



The transparent metal (b) passes back into the scale form (a) under certain 

 kinds of mechanical or chemical treatment. 



The metals already examined include gold, silver, platinum, cobalt, nickel, 

 chromium, iron, copper, lead, bismuth, antimony, tin, cadmium, magnesium, 

 aluminium, zinc. 



The highly crystalline metals, such as antimony, bismuth, and zinc, exhibit the 

 same features as the softer and more malleable metals. The crystalline faces and 

 cleavage planes are covered with a film of transparent metal, while scales are dis- 

 tinctly seen in fractures at right angles to the cleavage planes. 



Galena shows similar appearances. 



The zinc and tin alloys of copper show the same minute structure and appear- 

 ances. 



The persistence of these minute scales under all kinds of mechanical and 

 thermal treatment, the remarkable uniformity of their size and appearance in 

 metals of all of the leading groups, their disappearance into the transparent form 

 and their reappearance agaii' apparently imchanged in size or otherwise — all this 

 seems to afford fair ground for the conjecture that they are in some way definite 

 units in the structure of metals. 



5. On the Action of Ammonia on Metals at High Temperatures. 

 By G. G. Henderson, D.Sc, and G. T. Beilby. 



Platinum, gold, silver, copper, iron, nickel, and cobalt have been exposed to 

 the' action of ammonia at temperatures ranging from 600° to 900°. In every case 

 the physical effect of the treatment was to disintegrate the metal completely, while 

 a large proportion of the ammonia was resolved into its elements. 



The fracture of metals which have been exposed to this action has been 



