Scientific Intelligence. 177 
Neither is alumine essential; for I prepared a very good pyro- 
phorus with 1 atom of sulphate of potash, 3 atoms of sulphate of 
magnesia and lamp black. 
Sulphuret of potassium, with one or several atoms of sulphur, or 
even an oxysulphuret, not inflaming in the air when in mass; and 
the presence of alumine and magnesia appearing to me to have no 
other agency than that of dividing the sulphuret of potassium, it 
seemed to me that I might advantageously replace these two bases | 
by charcoal. Accordingly with 25.3 of sulph. of potash 1 at. 
7.5 of lamp black 4 at. 
I obtained a sulphuret in mass, not inflammable; but, by doubling 
the dose of lamp black, I had a pulverulent matter, which inflamed 
even in dry air with astonishing rapidity. This matter is composed 
of polysulphuret of potassium and potash intimately mingled with 
carbon. It is more inflammable than common pyrophorus, because 
the carbon being itself combustible, does not remain passive in the 
phenomenon, like alumine and magnesia; the ignition having com- 
menced, it feeds it. 
Sulphate of soda, treated with lamp black, gives a pyrophorus, but 
sulphate of barytes yields none.Idem. 
19. Joduret of Calcium and Potassium. (J. de Phar. 1828. p. 
44.)—In mixing together 14 part of quick lime, which is to be slack- 
ed in water, with 1 part of iodine, and 2 to 3 parts of water, there 
is formed ioduret of calcium which remains in the liquid, and iodate 
of lime insoluble, which mingles with excess of lime. , 
In decomposing the ioduret of calcium by carb. of potash, we ob- 
tain ioduret of potassium, pure.—Idem. 
20. Instructions relative to the art of Refining. Two memoirs 
published in 1827 and 1828; by M. D’Arcet, Assayer of the Mint, 
. Paris.—The art of refining is that of separating gold and silver from 
metals of less value, with which they are combined. It has been 
practised from the earliest periods of the metallurgic arts. 
The method formerly used was to melt the ingot of metal to be 
refined, with saltpetre, in order to separate the oxydable metals. It 
was then converted into grains, which were heated in earthen vessels 
at first with weak nitric acid, and in a second operation with that 
which was more concentrated. ‘The gold alone remained undissoly- 
Vou. XVH.—No. 1. 23 
