i 



Carbon at high Temperatures and Pressures. [June 14, 



irated with oil, soft crystals of graphite exuded from specimens 

 brat had been kept for some weeks. 



No. 2. Pure hydrated alumina, carbonate and oxide of magnesia 

 and lime all rapidly destroyed the carbon rod, by combining with it, 

 the hydrated alumina forming large volumes of gas of which it 

 appeared to be a constituent. On account of the great diminution of 

 bulk, no analysis was made ; the gas issued from the mould explo- 

 sively at from 10 to 12 tons per square inch. The alumina was found 

 in a crystalline crust, like sugar, around where the rod had been. 

 Hardness that of corundum, almost translucent. 



~No. 3. The following is the most interesting experiment of the 

 series : — 



On the botton of the mould was a layer of slaked lime about 

 ^-inch thick, over this silver sand 2 inches, then another layer of 

 lime of the same thickness as the former, finally a layer of coke-dust, 

 and then the plunger. With a pressure of from 5 to 30 tons per square 

 inch in the mould, and the carbon of from \ to T 5 -g diameter, currents 

 from 200 to 300 amperes were passed. 



In from 10 to 30 minutes the current was generally interrupted by 

 the breaking or fusing of the rod, or by the action of the lime in 

 dissolving it at the top or bottom. On opening the mould when it had 

 cooled a little, the silica usually appeared to have melted to an egg- 

 shaped mass, and mixed somewhat at the ends with the lime ; the 

 surface of the carbon appeared acted on, and sometimes pitted and 

 crystalline in places ; silica adhered to the surface, and beneath, when 

 viewed under the microscope, appeared a globular cauliflower-like 

 formation of a yellowish colour, resembling some specimens of 

 "borfc."* 



After several days' immersion in concentrated hydrofluoric acid, this 

 formation remained partly adherent to the carbon ; on the surface of 

 the carbon was a layer or skin about ^th of an inch thick of great 

 hardness, on the outside grey, the fracture greyer than the carbon, 

 but having a shining coke-like appearance under the microscope. 



The powder scraped off the surface of the rod has great hardness, 

 and will cut rock crystal when applied with a piece of metal faster 

 than emery pow^der. It has, under the microscope, the appearance 

 of bort, the minute particles seem to cling together ; they are not 

 transparent as a rule, and though some such particles are found 

 among them, it is not clear that such are hard. 



When a piece of the skin has been rubbed against a diamond or 

 other hard body, the projecting or hard portions have a glossy coke- 

 like appearance. 



A piece of the skin will continue to scratch rock crystal for some 

 time without losing its edge. It will scratch ruby, and when rubbed 

 * The bort-like powder is not acted on by hydrofluoric and nitric acids mixed. 



