260 Progress in Science. (April, 
a communication is established with the fire-grate on the one hand and the 
chimney on the other. The sides are built up of a number of flanged plates, 
bolted together into a polygonal form, and cast with honeycombed or cellular 
sides so as to form cavities for receiving and securely holding the fettling with 
which the converter is lined. This fettling consists chiefly of mill-furnace 
cinder, or ball-furnace tap; and having been melted in a cupola furnace, is 
either run direétly into the converter or moulded into masses, which when cold 
fit the cavities in the sides. When the molten charge of cast-iron has been 
introduced into the converter, the charging-holes are closed, and the vessel is 
caused to revolve by means of large spur-wheels attached to the end-plates : 
the liquid metal becomes rapidly agitated against the flat sides, and in about 
half an hour the balls of wrought-iron may be removed, at least 6 cwts. of 
metal being turned out at each heat. 
Some improvements in mechanical puddling-furnaces have also been lately 
suggested by Mr. W. Ferrie, of the Monklands Iron Works. He causes the 
movable bed or hearth of the furnace to revolve by fixing to it a cylindrical 
flange which proje&s downwards into a circular gutter filled with water, 
sand, or ground fire-brick, by which means a connection is sealed between the 
fixed and the moving parts of the furnace, without interfering with the freedom 
of motion. 
An elaborate essay on the Metallurgy of Silver in Mexico, by M. P. Laur, 
has been published in two recent numbers of the “* Annales des Mines.” After 
noticing the mode of occurrence of the ores, the author describes in detail 
the several metallurgical processes used at the different works,—namely, 
amalgamation at ordinary temperatures by the fatio process; amalgamation 
in the cazo, or vessel containing a boiling solution of common salt; and the 
old Saxon process of amalgamation with iron in rotating barrels. M. Laur 
raises many objections to the generally-received theory of amalgamation by 
the patio process, and advances an original view of the reactions which occur 
in the patio. It may be well to state that the torta, or heap of materials used 
in the reduétion of the silver ores by this method, consists essentially of a 
mixture of common salt, ‘“‘ magistral”” or roasted copper pyrites, mercury, and 
silver ores usually in the state of sulphides. According to most metallurgical 
chemists, the chloride of sodium and the sulphate of copper in the magistral 
react upon each other, and thus produce sulphate of soda and chloride of 
copper: this chloride then converts the sulphide of silver into a chloride, 
which dissolves in the salt water present in the torta ; the mercury then rapidly 
attacks the solution of chloride of silver, reducing the metal and becoming in 
turn converted into calomel, whilst the free silver forms, with some of the un- 
altered mercury, an amalgam, which is retorted, and the mercury distilled off 
while the silver remains behind. Modifications of this theory have been pro- 
posed, but the essential points remain—that the silver is formed into a 
chloride, and this is decomposed by the mercury. M. Laur’s Mexican expe- 
rience leads him to believe, on the contrary, that the sulphide of silver is 
reduced directly to the metallic state, and does not pass threugh the interme- 
diate condition of a chloride. By the reaction of the magistral with the salt, 
sulphate of soda and protochloride of copper are formed :— 
NaCl+ Cu0.SO3 = NaO.S034 CuCl. 
This chloride is then reduced to the state of a sub-salt, which combines with 
the sodium chloride to form a double salt— 
2CuCl+ NaCl+Hg = NaCl.Cu,Cl + HgCl. 
The double salt reacts dire@ly upon the silver sulphide, and effects its 
reduction :— 
NaCl.Cu,Cl+AgS = NaCl.CuCl+CuS+Ag. 
The protochloride of copper passes again to the state of subchloride, while the 
sulphide of copper is oxidised into sulphate, and the cycle of change thus 
commences afresh. 
Messrs. Hargreaves and Robinson, of Widnes, have patented certain im- 
provements in the method of treating metallic sulphides, especially pyrites, 
