112 
laminar form as the other. This specimen is very beauti- 
ful and singular. 
Specimen No. 5. The mammillar form appears lost. 
The carbon has great hardness, equal to black marble, 
and the fracture is stony without any laminae. 
Specimen No. 6. Another appearance is presented of 
great metallic brilliancy, density, and hardness. 
Specimen No. 7 is the same form as deposited on the 
charred broom, in needle-shaped ramifications, and when 
magnified is like a string of beads, very hard, elastic, and 
composed of pure carbon ; at least I have been unable to 
detect any foreign substance, and there is no appearance 
of sulphur when heated. 
Specimens Nos. 3, 4, 5, and 6, contain iron in a metallic 
state, but varying considerably in different specimens. No. 
5 contains the greatest amount. 
These forms of carbon will bear the most violent heat 
with very little waste. In my crucible furnace, urged with 
a large circular fan, raised far beyond a forge fire, it 
suffers but little waste, and gives an intense heat. Formed 
into crucibles, by a lump being cut hollow in a lathe, it is 
most valuable, standing where all others fail. The forms 
of this carbon, as shown in Nos. 5 and 6, are what I 
prefer in the voltaic battery, and may be obtained at any 
gas works at the most trifling cost, in plates of large size, 
and suflSciently thin to use in the square cells. 
The most convenient form, and involving the smallest 
cost, also preferable in many respects, is to cut the carbon 
into sticks of about 1|- inch diameter, and 7 long, and use 
them with the nitric acid in round porous cells, the sur- 
rounding zinc cylinders being about three inches in diameter. 
The cutting of the carbon is accomplished with the greatest 
facility and certainty, by the machine of a marble cutter, 
at the small cost of l;^d. each, and can easily be obtained 
