242 
ME. GEORGE GOEE ON ELUOEIDE OE SILVER. 
I conclude, therefore, that chlorine does not set free fluorine from fluoride of silver at 
a low red heat in vessels of gold or platinum, but unites chemically with that salt and 
with the metal of the vessel to form a compound from which fluorine is not set free at 
a low red heat. 
I now tried a method of getting boats of pure carbon in order to repeat the foregoing 
experiment. The method consisted in making boats of lignum-vitae, baking them very 
gradually until they were quite black and evolved no visible liquid, then heating them 
with extreme slowness in a nearly closed copper tube, with frequent turning until the 
tube was quite red-hot, and cooling them very slowly. On heating fluoride of silver in 
one of them inside a platinum tube-retort, it became nearly wholly reduced to metal, 
probably in consequence of the presence of hydrogen in the boat. To purify the boats 
from that substance, a number of them were heated to redness in a porcelain tube with 
a current of chlorine passing over them during three hours ; nearly the whole of them 
fell to pieces during the process. 
I also obtained a large variety of specimens of native graphite, and made many boats 
from the purest and hardest varieties*, and also from selected pieces of gas-carbon f. To 
purify them, they were digested about six days in hot concentrated hydrochloric acid 
until soluble matter ceased to come out, then in boiling water, then in cold and pure 
aqueous hydrofluoric acid during six days, and again in boiling water until all acid was 
removed. They were now dried and ignited to expel sulphur ; and to remove hydrogen 
they were heated to redness in a platinum tube-retort in a current of bromine J vapour 
during more than one hour ; and to remove any remaining silica they were similarly 
heated in vapour of pure aqueous hydrofluoric acid during one hour ; then finally heated 
to redness in an open platinum tube. Boats thus prepared had no chemical effect upon 
melted fluoride of silver at a low red heat, provided they were heated to redness imme- 
diately before use. 
The following kinds of native graphite were tried. Ceylon graphite ; the hardest 
specimens were too fragile. Graphite from Iceland ; much too impure. Compressed 
Cumberland graphite; fell to powder when heated in hydrochloric acid. Graphite 
from Greenland ; split into layers in the process of carving. Sidoroff’s graphite from 
the Lower Tongooska Biver, Siberia § ; boats made of it cracked when heated with fluoride 
of silver in chlorine. Graphite from “Marbella, Andulasia,” also a specimen of “Siberian 
graphite ”|| ; formed good boats, but were rather soft. Excellent boats were made from 
a specimen of “ Graphite from Spain;” but the best were made from Alibert’s graphite 
from Irkoutsk, and that from Borrodale. Many specimens contained veins and nodules 
of quartz. 
* The best I have found have been the purest varieties of Axibert’s Siberian plumbago, obtained from Messrs. 
Eaber, of Stein, near Nuremberg ; and also selected pieces of Borrodale graphite. 
t Boats of this substance have been made for me in a satisfactory manner by Mr. J. Thorp, 3 Charles Street, 
"Wandsworth Read, London. 
+ If chlorine was used the boats became covered with minute spangles of platinum. 
§ Given to me by Mr. Brandt, Palmerston Buildings, Bishopsgate Street, London. 
|| Given to me by the Plumbago Crucible Company, Battersea, London. 
