almost pure. One of its most common ores is galena, or of a reverberatory furnace, in which the fire is represented native sulphuret of silver and lead. This mineral may be burning at B, and darting its flames down upon the subprocured of any dealer in minerals, and the student will do stance A. well to obtain a specimen, in order to prosecute the following experiments illustrative of the actual processes had recourse to in practice for extracting the respective metals. Taking a little fragment of galena about the size of a pea, deposit it on a piece of charcoal and direct upon it the flame of a spirit-lamp or candle, urged by the blowpipe; remark how, under this treatment, some volatile substance is evolved, and try to recognise the odour of the vapour. Possibly, however, this recognition cannot be satisfactorily arrived at, for I may remark that the sensation of heat so confounds the acuteness of smell, that experienced operators are sometimes deceived when attempting to recognise the odour of a very hot body. Should there be any difficulty experienced in this respect, proceed as follows. Take a piece of glass tube, about six inches long and about the fourth of an inch in internal diameter; bend it as represented in the subjoined woodcut, fig. 31; deposit a fragment of galena in the bend, as depicted, Fig. 31. Fig. 32. Having dissipated every portion of volatile matter from the fragment under treatment, next powder it, rinse it with a small portion of washing soda and borax, and fuse it by means of the strongest portion of the blowpipe jet into a metallic bead, using, during the operation, a charcoal support. Finally, this bead may be cupelled by means of the blowpipe flame directed down upon some bone earth rammed into a tobaccopipe as described already. The student will not do ill in preparing several beads of this kind. One of these he may subject to the process of cupellation, the others he may analyse by as many variations of the moist procees as suggest themselves. At least two distinct processes of accomplishing the separation of silver from lead will at once occur to him if he have studied, practically, certain facts already detailed. I shall leave him with the hint to consider the distinctive properties of chloride of lead and chloride of silver. He will surely now experience no difficulty in effecting the moist analysis. apply a strong spirit flame, and applying the nostril to the cold open extremity, the odour will be easily referrible to that of burning sulphur. This, it may be remarked, is the best way of testing the odour of any mineral body under the application of heat. By applying a temperature of sufficient intensity and for a period sufficiently long, all the sulphur and other volatile matters (probably arsenic may be present) will be driven away. The operation of applying heat for this purpose is called, in the technical language of mineralogy, "roasting." Although our bent glass tube is a very proper device for enabling the operator to discriminate, by smelling, the nature of the fumes evolved, it is not the best for insuring the development of the lost portions of sulphur; to which end the heat thus capable of being applied would be scarcely powerful enough. It will be preferable, therefore, having ascertained the presence of sulphur in the ore, to complete the roasting process on a piece of charcoal before the blowpipe flame, care being taken not to urge the temperature to the extent of fusing the sulphuret, under which circumstances the number of points of contact between the air and the mineral would become diminished, and the conversion of sulphur into sulphurous acid would be retarded. In practice, the operation of roasting is performed by furnaces termed reverberatory; that is to say, the flame of which is caused to reverberate or impinge against the body to be operated upon. The general idea of a reverberatory furnace may be obtained by reference to the appended sketch, fig. 32, being a sectional representation "FOLLOW ME." Sailor on life's troubled sea, Turn from earthly things away- Trav'ller on the road of life! Pilgrim through this vale of tears, Wand'rer! they have charms for thee; C. P. ILLSLEY, (amended.) This entry is rendered necessary from the circumstance that both the parties whose names appear were debited for the cost of Insurance in July, and they are again charged for the same cost in the account of the sales in the preceding entries. They must accordingly be only once charged in the Ledger, and this entry effects the required purpose. |