com,K.

337

[ at its bottom, c316 .1

/

h*’ a ?" 00c | en chimney which Stands in the centre of the mound with a small pile ofarcoal at its bottom, r ■ d d are large lumps of ore surrounded by smaller pieces; f f

are rubbish and earth to form a covering.j, A current of air is admitted under the

^ billets by an opening in the middle of

each- of the four sides of the base a a,so that two principal currents of aircross under the vertical axis c of theJ truncated pyramid, as indicated in the

T , - . c “ figure-

r ne ure is applied through the chimney c j the charcoal at its bottom c, and the piles® a are kindled. The sulphureous ores, d f, are raised to such a high temperature as0 expel the sulphur in the state of vapor.

la the Lower Hartz a roasting mound continues burning during four months. Somea ys after it is kindled the sulphur begins to exhale, and is condensed by the air at thePPer surface of the pyramid. When this seems impregnated with it, small basins 1 1re excavated, in which some liquid sulphur collects; it is removed from time to time• . won ladles, and thrown into water, where it solidifies. It is then refined and castlnt o roll brimstone.

A Similar roasting mound contains, in the Lower Hartz, from 100 to 110 tons of oresul u '® cu fi*c feet of wood. It yields in four months about one ton and a half of,P{ lur from copper pyrites. Lead ore is treated in the same way, but it furnishes lessSUI Phur.

Wr?p ere are usually f rom 12 to 15 roasting heaps in action at once for three smeltingwh't Lower Hartz. After the first roasting two heaps are united to form a third,Ute'tv 5 ca ^ c * ne fi a new, but under a shed; the ores are then stirred up and roasted for*uird time, whence a crude mixture is procured for the smelting-house,best ttost fi avora fil e seasons for roasting in the open air are spring and autumn; the"feather is a light wind accompanied with gentle rain. When the wind or rainnp-cts the operation, this inconvenience is remedied by planks distributed round theP^. r surface of the truncated pyramid over the sulphur basins.te Pr ^ nu -^ actur i n S assays of copper .—The first thing is to make such a sample as willdig- sei *t the whole mass to be valued; with which view, fragments must be taken fromtried s P°ts, mixed, weighed, and ground together. A portion of this mixture beingar son'^ le blow-pipe, will show, bv the garlic or sulphurous smell of its fumes, whether100 7 ’ sul P h «. or both, be the mineralizers. In the latter case, which often occurs,then j', or gr. of the ore are to be mixed with one half its weight of saw-dust,dis s j B ® bae fi with oil, and heated moderately in a crucible till all the arsenical fumes beearth en ea ‘ The residuum, being cooled and triturated, is to be exposed in a shallowteninip *° a slow roasting heat,rill the sulphur and charcoal be burned away. What''veigj 1[ s ’ b pi n g ground and mixed with half its weight of Calcined borax, one twelfth itsdown in* black, next made into a dough with a few drops of oil, is to be pressed?°Werf u i ° 3 crucible, which is to be covered with a luted lid, and to be subjected, in aOn coolin' 111 ^ urnace > first to a dull red heat, and then to vivid ignition for 20 minutes,color and ? and breaking the crucible, a button of metallic copper will be obtained. Itsraln e of , IBa ^l ea bility indicate pretty well the quality, as does its weight the relativeSold. s„” e . ore - It should be cupelled with lead, to-ascertain if it contains silver orIf the tj ASSAY > and Silver .

"either sul°T" I,lpe l ” a * showed no arsenic, the first calcination may be omitted j and if®*rectly with nor arsen i c > a portion of the ground ore should be- dried, and treatedc °Pper ores ]/ orax > lamp-black, and oil. It is very common to make a dry assay ofWe ight of th one , roast ing and one fusion along with 3 parts of black flux Irom hrT he humid me,a ^. ,c button the richness of the ore is inferred.

,, The sulnhi assa y * s more exact, but it requires more skill and time.th 1 ’ bat onlv silica are easily got rid of by the acids, which do not dissolve

eYrWp down h h metallic oxydes and the other earths. These oxydes may then bes “ e t the black ' appropriate reagents, the copper being precipitated in the state ofto el °re entering or P ur e metal. 105 parts of black oxyde represent 100 of copper.

a scert a ; n wh f 011 complete analysis of an ore, preliminary trials should be made,oa, Ites > Without s ] 816 ltS constituents. If it be sulphuret of copper, or copper<W * reate d in a m V . er or lead, 100 grains exactly of its average powder may be weighed°f nitric aci l im S Wlt ^ boiling muriatic acid for some time, gradually adding a fewup - found floatin • a ^ action ceases, or till the ore be all dissolved. The insolublebu st w a fi ltcr, wash Jj”. ? e Hricid contains most of the sulphur; it may be separatedtoh„ fesiduum , e ,; an d weighed; then verified by burning away. The incom-added to the'fom/ 011 T- mUriat * c acid, may. leave an insoluble deposite, which iser. To the whole of the filtered solutions carbonate of potash is22