226

SMELTING IRON FURNACES.

between the grate and the brim. The grate is 2 feet long and 8J inches wide. Allthe caldrons have the same elliptic form, with a bottom like the small end of an egg.The fifth alone is smaller, but this one serves merely to melt the lead which has beenstripped of its silver, in order to be cast into salmons or blocks.

The charge consists of 64 or 65 salmons, each weighing from 120 to 140 lbs. Whenthey are well melted, the fire is removed from the grate, as well as the small film oflitharge from the surface of the metal; and one or two salmons are added to acceleratethe cooling, or sometimes, instead, a little soapy water is sprinkled into the caldron,whereby a crust of lead is formed, which being pushed down into the mass, melts withebullition. This is repeated till the whole becomes sufficiently cool, that is, whencrystals begin to form. The lead concreted round thfr sides being now detached, thewhole is stirred with an iron bar, by a motion in a vertical plane, and varying itsposture in this plane. During this operation, intended to establish a uniform tempera-ture throughout the mass, a second workman heats in the smaller pot adjoining toNo. 1 a large skimmer at the end of a long wooden handle, and next proceeds to fishout the crystals, taking care to let them drain off for a few seconds all the liquid leadamong them, and then turns out the crystals slowly into the next caldron, No. 2;the second workman meanwhile adds the metal solidified round the sides, and stirs alltogether to equalise the temperature. These two-fold operations occupy about fiftyminutes ; by which time, there remains in the caldron about 16 salmons. The workmannow lifts out the crystals, as before, with the drainer, and throws them upon the groundin two heaps. His assistant takes them up a little while afterward, and puts themaway to make room for fresh crystals, .which the first workman continues to throwdown. This process goes on till only 8 salmons remain in the caldron, a point ascer-tained by gauging the height to the bath. The fire being at this time removed fromcauldron No. 2 into the grate of No. 1, the 8 salmons of lead enriched with silver,which remain at the bottom of the caldron, are run out into movable moulds; and the8 salmons which were thrown upon-the ground are pu*into it; the full charge beingthen made up with salmons of the same richness as those previously used.

While this mass is melting in No. 1 the process just finished in it is repeated inNo. 2. About three fourths of the metallic mass is next separated in the state ofcrystals, which are transferred to No. 3, and also one eighth of crystals thrown on theground, after pouring the remaining one eighth at the bottom of caldron No. 2 notinto moulds, but into No. 1.

A like process is performed in caldrons 3 and 4; and the poor lead taken out of 4is transferred to 5 to be melted, and run into salmons, which are submitted afresh to th epreceding series of «rystallizations, provided the lead still contains a sufficient proporti° nof silver.

The following Table will place the results of the above successive operations in aclear light:—

Silver in 1 Ton of Lead.

Original lead - - - - - 0-001153

1. Rich crystals - - - - - - 0-003324

2. Poor ditto 0-000933

—Rich ditto 1 proceeding from the, treatment of the prece-( 0-0020802

3. Poor ditto $ ing No. 2 poor crystals - - ( 0-0007021

4. Rich ^proceeding from the treatment of No. 3 poor crys-( 0-001399

—Poor 5 tals - - - - - - ( 0-0004569

—Rich 1 r* at a ( 0-0008135

(Lead) poor \ as above from No ' 4 ' ' ' \ 0-0001128

We thus see, that four crystallizations, repeated upon the original lead f r 9!?. t ? asmelting furnace, of the above richness, will afford a lead ten times poorer. W glead originally containing only 0-0002248 in silver, three crystallizations would suto make it ten times poorer. In general, the poorer the lead, within certain limw s >better adapted is it to this process.

SILVERING . See Electrotype. odern

SLIDES. The name given by the Cornish miners to clay veins of more mformation. e,.veral

SMELTING IRON FURNACES, commonly called BLAST FURNACES, ofof these furnaces, as mounted near Glasgow , deserve to be made known, on acc ^irthe economy of their construction, the advantage of their form, and the amount o

performance. tine at the

Fig. 126 represents one of the smallest of these, which measures from the J it

bottom to the top 48 feet, from which all the other dimensions may be estim pigs.produces a soft cast iron for casting into moulds and for melting in the cupo a. C, V127 and 128 represent a much larger furnace, being from the top, to the line A, >