78 THE HON. SIR CHAELES ALGERNON PARSONS: EXPERIMENTS ON 



smelted by the heating carbon rod or by the associated hydrocarbons, &c., when such 

 were added, and iron globules were formed. In these, diamond was occasionally 

 found when cooling was rapid and they were centrally situated in the charge. 



Very Quick Cooling. To test the action of very quick cooling a carbon crucible of 

 2-inch internal diameter charged with iron, sugar carbon, 2 per cent, silicide of carbon, 

 well boiled by resistance heating under atmospheric pressure and 2 per cent, of iron 

 sulphide added, was quickly placed on asbestos mill-board resting on a steel table 

 frictionally held in the bore of the 4-inch mould, below being placed 2 Ibs. of carbon 

 dioxide snow, and the plunger quickly brought down by the press, subjecting the 

 whole to 6000 atmospheres pressure. When taken out the crucible was intact, the 

 contents had divided into a lower portion consisting of a large grained crumbling 

 mass of graphite admixed with granules of very hard iron, in the centre a rounded 

 pillar of white iron equally hard. The cooling seemed to have been unusually rapid. 



The experiment was repeated, the crucible being charged with iron, sugar carbon, 

 5 per cent, manganese, 5 per cent, cobalt, 2 per cent, silicide of carbon, boiled, and 

 2 per cent, iron sulphide added. 



It was also repeated with water instead of carbon dioxide snow. The result of all 

 these experiments was similar to the first. No diamond was found in any part. 



An experiment which seemed to give practically instantaneous cooling was as 

 follows : A small carbon crucible containing iron, with traces of silicon, aluminium, 

 calcium, magnesia and sulphur, was floated on a carbon block on a bath of mercury, 

 all contained in a vessel exhausted to 2 mm. absolute. The crucible was heated 

 by an arc from an upper carbon, the holder passing through a stuffing box. When 

 the crucible was sufficiently hot and the contents carburized, the upper carbon was 

 thrust down, submerging the crucible under the mercury ; the cooling was almost 

 explosive and instantaneous the finely divided iron and graphite on analysis yielded 

 no diamond. 



Extremely rapid cooling does not, therefore, seem to be a direct cause in the 

 production of diamond. 



Experiments at Atmospheric Pressure. 



A convenient method of studying the effect of the association of other elements 

 with iron on a small scale uncontaminated by the vapours of a furnace lining 

 suggested itself, and a series of experiments were made as follows : A deep iron dish 

 was packed tightly with Acheson graphite with a slight dimple in the centre to hold 

 the ingot, above, graphite was filled in loosely to a depth of half an inch covering the 

 ingot. An arc was struck by a carbon on to the ingot submerged in the loose 

 graphite. When the iron was well boiled the surrounding graphite with the ingot 

 in it was dug out entire and thrown into a bowl of mercury covered with water. 



The results showed that, using ordinary mild steel, no diamond ever occurred on 

 analysis, but that a small percentage of silicon is absolutely essential; small 



