ROCK-DRILL 



709 



1717 



reduced, the mineral, from continuing to pass at the same rate through the furnace, 

 cannot be properly calcined. 



To prevent the fires getting low, and to raise 

 them after being neglected, the -workmen often 

 load the grate with fuel, the result of which is to 

 overheat the ore and cause a great waste of wood. 



Figs. 1715, 1716, and 1717 represent a re- 

 verberatory furnace employed in the smelting 

 works of Lautenthal, in the Hartz, for roasting 

 the schlichs of lead ores, which contain much 

 blende or sulphide of zinc. In fig. 1715 we see 

 that the two sides, are absolutely like, the two 

 furnaces being built in one body of brickwork. 

 Fig. 1716 is the plan of the furnace nc, taken 

 at the level EF of fig. 1715. Fig. 1717 is a 

 vertical section of the similar furnace A B, taken 

 in the prolongation of the lino OH in fig. 1716. 



a is the fireplace of the furnace, its grate, 

 and ash-pit, b is the conduit of vaporisation, 

 which communicates with the chambers c; into 

 which the vaporised substances are deposited; 

 d, chimney for the escape of the smoke of the 

 fireplace a, after it has gone through the space 

 bcc ; e' is the charging door, with a hook hang- 

 ing in front to rest the long iron rake upon, 

 with which the materials are turned over; /, 

 chamber containing a quantity of schlich destined 

 for roasting ; this chamber communicates with the vaulted corridor (gallery) D, seen 

 in fig. 1715 ; g, orifice through which the schlich is thrown into the furnace ; h, area 

 or hearth of the reverberatory furnace, of which the roof is certainly much too high ; 

 i, channels for the escape of the watery vapours ; k I, front arcade, between which and 

 the furnace, properly speaking, are the two orifices of the conduits, which terminate at 

 the channels m in', m is the channel for carrying towards the chimney, d, the vapours 

 which escape by the door e'. n is a walled-up door, which is opened from time to 

 time, to take out of the chambers c, c, the substances that may be deposited in them. 



At the smelting-works of Lautenthal, in such a roasting-furnace, from 6 to 9 

 quintals (cwts.) of schlich are treated at a time, and it is stirred frequently with an 

 iron rake upon the altar h. The period of this operation is from 6 to 12 hours, 

 according as the schlich may be more or less dry, more or less rich in lead, or more or 

 less charged with blende. When the latter substance is abundant, the process requires 

 12 hours, with about 60 cubic feet of cleft billets for fuel. 



In such furnaces are roasted the cobalt ores of Schneeberg in Saxony, the tin ores 

 of Schlackenwald in Bohemia, of Ehrenfriedersdorf in Saxony, and elsewhere ; as also 

 the arsenical pyrites at Geyer in Saxony. But there are poison towers and extensive 

 condensing chambers attached in the latter case. 



For a description of Gerstenhofer's furnace for roasting metallic sulphides, see 

 COPPER. 



ROCCELLA, from the Italian rocca, ' a rock ; ' a genus of lichens. See ABCHTL j 

 LICHENS. 



ROCCEXiLIC ACID. A fatty acid obtained from the Roccetta tinctoria, 



ROCHEL1.E SALT. A double tartrate of soda and potash : mixed with soffld 

 carbonate of soda, and an equivalent of tartaric acid being added, after the salt is 

 dissolved, it forms the artificial seidlitz-water. 



ROCK or ROCK ALUM, A factitious article consisting of crystalline frag- 

 ments of alum not larger than almonds, coloured with Venetian red. See ALUM. 



ROCK. A term used in South Staffordshire by miners to denote any hard sand- 

 stone. 



ROCK CRYSTAL. A very fine transparent and colourless variety of quartz. 



ROCK-BRILL or PERFORATOR. The rock-drill invented by Mr. Ingersol 

 has achieved a high reputation in the mines of America. It has been introduced to 

 this country by Messrs. Le Gros and Silva, and having excited much attention must 

 be briefly described. 



The chief principles and characteristic features of this rock-drill are, that the 

 motive pressure is continued until the ttroke of the piston takes effect in a blow on 

 the rock (in lieu of being cut off at a point antecedent to tho rock being struck), 

 whereby an important accession of speed in penetration is attained ; and that the feed 

 or forward motion of the machine is strictly and completely automatic, dependent 



