The slag created by the ash-furnace is a heavy, black, glassy substance, well melted, and still containing a portion of lead. Some attempts have been made to obtain a further portion of lead from it, by smelting with charcoal in a blast-furnace; but the undertaking has not been attended with complete success, and is not generally thought to warrant the expense. The per centage of lead recovered from the slag is not estimated at over ten, and, with the utmost success, cannot be reckoned to exceed twelve.
Some practical and miscellaneous observations may here be added. Metallic lead in the pig is now (Feb. 1819) worth $4 per cwt. at the mines. It sells for $4 50 on the banks of the Mississippi, at St. Genevieve and Herculaneum; for $5 50 in New Orleans; and is quoted at $6 in Philadelphia. This is lower than has ever been known before, (except at one period,) and a consequent depression in the mining business is felt. There is a governmental duty of one cent per pound on all bar and pig lead imported into the United States; but it does not amount to a prohibition of foreign lead from our markets. Perhaps such a prohibition might be deemed expedient. It is what the lead-smelters here call for; and certainly the resources of this country are very ample, not only for supplying the domestic consumption, but for exportation.
Those who dig the ore do not always smelt it. The merchants are generally the smelters, and either employ their own slaves in raising the ore, or pay a stipulated price per cwt. to those who choose to dig. For every hundred pounds of ore, properly cleaned, the digger receives two dollars. He works on his own account, and runs the risk of finding ore. It is estimated that an ordinary hand will raise a hundredweight per day, on an average of a year together. This, however, depends much upon luck; sometimes a vast body is fallen upon, with a few hours' labor; at others, many weeks are spent without finding any. He who perseveres will, however, generally succeed; and the labor bestowed upon the most unpromising mine, is never wholly lost. The above average has been made by those long conversant with the business, and upon a full consideration of all risks.
Custom has established a number of laws among the miners, with regard to digging, which have a tendency to prevent disputes. Whenever a discovery is made, the person making it is entitled to claim the ground for twenty-five feet in every direction from his pit, giving him fifty feet square. Other diggers are each entitled to twelve feet square, which is just enough to sink a pit, and afford room for throwing out the earth. Each one measures and stakes off his ground, and, though he should not begin to work for several days afterwards, no person will intrude upon it. On this spot he digs down, but is not allowed to run drifts horizontally, so as to break into or undermine the pits of others. If appearances are unpromising, or he strikes the rock, and chooses to abandon his pit, he can go on any unoccupied ground, and, observing the same precautions, begin anew. In such a case, the abandoned pit may be occupied by any other person; and sometimes large bodies of ore are found by the second occupant, by a little work, which would have richly rewarded the labors of the first, had he persevered.
In digging down from fifteen to twenty feet, the rock is generally struck; and as the signs of ore frequently give out on coming to the rock, many of the pits are carried no further. This rock is invariably limestone, though there are many varieties of it, the texture varying from very hard and compact, to soft and friable. The former is considered by the diggers as a flinty stone; the latter is called rotten limestone; and, from its crumbling between the fingers, and falling into grains, there is a variety of it called sandstone. It is all, however, a calcareous carbonate, will burn into quicklime, and, as I find on experiment, is completely soluble in nitric acid. As no remains or impressions of shells, animalculæ, or other traces of animal life, are to be found in it, I conclude it to be what geologists term metalliferous limestone; a conclusion which is strengthened by its semi-crystalline fracture. It exhibits regular stratification, being always found in horizontal masses. How far this formation extends, it would be difficult to determine; but, so far as my observation goes, it is invariably the basis on which the mineral soil at Mine à Burton, and the numerous mines in its vicinity, reposes. It is overlaid by secondary limestone in various places on the banks of the Mississippi, between Cape Girardeau and St. Louis. It is also seen passing into a variety of secondary marble, in several localities. I have seen no specimens of this mineral, however, which can be considered as a valuable material in sculpture.
I have already mentioned the per centage of lead obtained by smelting in the large way. I shall here add the result of an assay made on the ore. One hundred parts of ore yielded as follows:
| Metallic lead | 82 | |
| Sulphur driven off by torrefaction | 11 | |
| Earthy matter, and further portion of sulphur, either combined with the scoria, or driven off by heat | 7 | by estimation |
| 100 |
The ore experimented upon was the common ore of Mine à Burton, (galena.) I took a lump of the purest ore, completely freed from all sparry and other extraneous matter, beat it into a very gross powder, and roasted for an hour and a half in a moderate heat, with frequent stirring. On weighing the mass, it had lost 11 of sulphur. I now beat this to a very fine powder, and treated it with a strong flux of nitre and dry carbonate of soda, adding some iron filings to absorb the last portions of sulphur. The whole was enclosed in a good Hessian crucible, previously smeared with charcoal, with a luted cover, and exposed for twenty minutes to the high heat of a small chemical blast-furnace.
The richest species of galena, of which we have any account, is that of Durham, England. An analysis of a specimen of this ore by Dr. Thompson, gave the following result:
| Lead | 85 13 |
| Sulphur | 13 02 |
| Oxide or iron | 0 5 |
| 98 65 |