1888.] Carbon at high Temperatures and great Pressures. 321 



Results. — In some of these experiments a. considerable quantity of 

 gas was generated, and the press had to be slightly slacked back 

 during the experiment to accommodate it and maintain the pressure 

 constant. 



In ail cases there was a soft friable black deposit of considerable 

 thickness on the carbon. 



In no case was the specific gravity of the carbon rod increased by 

 this process. There was no change in appearance of the fracture, ex- 

 cepting when chloride of carbon had been the fluid; it was greyer in 

 this case. 



The rate of burning of samples placed in arc lamps was not 

 diminished by the process. Various rates of deposition were tried, 

 but with the same result, and the conclusion seems to be that under 

 very high pressures, such as from 5 to 15 tons per square inch, the 

 deposit of carbon by heat from hydrocarbons, chloride of carbon, 

 bisulphide of carbon, treacle, &c, is of a sooty nature, and unlike the 

 hard steel-grey deposit from the same liquids or their vapours at 

 atmospheric or lower pressures. 



Experiments. Class II. 



In these experiments the asbestos-rubber packing was omitted, the 

 plunger and spigot being an easy fit in the mould. A layer of coke 

 powder under the plunger formed the top electrical connexion with 

 the rod. 



No. 1. Silver sand or silica was run around the carbon rod, and 

 pressures of from 5 to 30 tons per square inch applied ; the rod was 

 usually about ^-inch diameter, and currents up to 300 amperes 

 passed. 



Results. — The silica was melted to the form of a small hen's egg 

 around the rod. When the current was increased to about 250 

 amperes the rod became altered to graphite, the greater the heat 

 apparently the softer the graphite. There was no action between the 

 silica and the carbon, the surface of the carbon remained black, and 

 there were no hard particles in or on the carbon rod. 



Other substances, such as an hydrated alumina and mixtures of 

 alumina and silica, gave the same results. 



The density of the carbon was considerably increased, in some cases 

 from normal at 1*6 to 2'2 and 2'4 ; in these cases the carbon appeared 

 very dense, much harder than the original carbon, and about as 

 hard as the densest gas-retort carbon. No crystalline structure was 

 visible. 



The specimens were treated with solvents, and there appeared no 

 indication of the surrounding substance having penetrated the rod ; 

 the carbon was undoubtedly consolidated by 30 per cent. 



In some cases when the material surrounding the rod was alumina 



