82 THE HON. SIR CHAELES ALGERNON PARSONS : EXPERIMENTS ON 



consisted of 95 per cent, carbon monoxide, 1 per cent, hydrogen, 2 per cent, hydro- 

 carbon, 2 per cent, nitrogen. 



The carbon which formed the crucible and cover contained a large percentage of 

 silica, but the carbon monoxide was produced chiefly by the action of sand (of which 

 there was a thick layer on the bottom of the container to protect the insulating 

 joint from iron spilled from the crucible) on the carbon of the stem of the crucible. 

 About one half of the iron had been evaporated, and there remained an ingot about 

 the size and shape of a broad bean. It contained rather large graphite crystals and 

 was easily broken. The analysis gave the largest residue of diamond in proportion 

 to the amount of iron of any of our experiments, the largest crystals being 0'7 mm. 

 in length. 



This experiment was repeated several times with the same result. The time of 

 cooling of the crucible, from switching off the current to the temperature of setting, 

 was 15 seconds, and probably sufficiently rapid to allow of a skin to be formed 

 around the ingot before the centre was solidified, for the configuration of the crucible 

 and cover were such as to ensure nearly equal and simultaneous cooling on all sides 

 of the ingot. At the time, vacuum was erroneously thought to be the chief 

 contributory cause and not the presence of carbon monoxide in large proportion. 



Higli Vacuum Experiments. 



The molecular pump not having yet been evolved, a powerful pumping system was 

 arranged, consisting of three steam-jet exhausters in series, the last ejector of the 

 series discharging into a jet condenser with separate air and water pumps, the former 

 assisted by a steam jet. The two steam-jet exhausters nearest to the exhausted 

 chamber were fed with highly superheated steam at 200 Ibs. pressure, and the 

 suction pipe to the chamber was 4 inches in diameter the chamber 2 feet 

 G inches diameter of spherical shape (fig. 11). A vacuum of mm. absolute could 

 be reached. 



The crucible was placed on a large block of carbon, resting on the base of the 

 chamber, and forming the bottom pole. The cover was insulated from the chamber, 

 and through an oil-sealed gland passed a 2-inch brass rod, carrying a crown holder, 

 with four 2-inch carbons which rested on the lip of the crucible for resistance heating. 

 An observation window was placed at the apex of a long iron cone, projecting from 

 the side of the cover, which gave a good view of the crucible and its contents. The 

 whole of the chamber was submerged in a tank of water, up to the level of the gland 

 in the cover. 



Iron and iron alloys were boiled and allowed to cool slowly by radiation, or were 

 rapidly quenched by admitting water through a large valve from the tank into the 

 vacuum vessel. The iron and carbon vapour from the boilings deposited dust and 

 globules on the cover and sides and bottom of the chamber. A very small diamond 



