Carbon at High Temperatures and Great Pressures. 305 



initial size of the rod was in all cases i inch, and the current 

 from 100 to 800 amperes. 



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 all cases there was a soft friable black deposit of con- 

 siderable thickness on the carbon. 



In no case was the specific gravity of the carbon rod 

 increased by this process. There was no change in appear- 

 ance of the fracture, excepting 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 w T ith 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 hydro- 

 carbons, 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 J 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 mix- 

 tures 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 22 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. 



