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BOOK VII.

not easily separated, is added sulphur and sand made from stones whicheasily melt.

Sal artificiosus 19 suitable for use in assaying ore is made in many ways.By the first method, equal portions of argol, lees of vinegar, and urine,are all boiled down together till turned into salt. The second method is fromequal portions of the ashes which wool-dyers use, of lime, of argol purified,and of melted salt; one libra of each of these ingredients is thrown intotwenty librae of urine ; then all are boiled down to one-third and strained,and afterward there is added to what remains one libra and four unciaeof unmelted salt, eight pounds of lye being at the same time poured intothe pots, with litharge smeared around on the inside, and the whole is boiledtill the salt becomes thoroughly dry. The third method follows. Unmeltedsalt, and iron which is eaten with rust, are put into a vessel, and afterurine has been poured in, it is covered with a lid and put in a warm placefor thirty days ; then the iron is washed in the urine and taken out, andthe residue is boiled until it is turned into salt. In the fourth method bywhich sal artificiosus is prepared, the lye made from equal portions oflim e and the ashes which wool-dyers use, together with equal portions ofsalt, soap, white argol, and saltpetre, are boiled until in the end the mix-ture evaporates and becomes salt. This salt is mixed with the concentratesfrom washing, to melt them.

Saltpetre is prepared in the following manner, in order that it may besuitable for use in assaying ore. It is placed in a pot which is smeared onthe inside with litharge, and lye made of quicklime is repeatedly poured overit, and it is heated until the fire consumes it. Wherefore the saltpetredoes not kindle with the fire, since it has absorbed the lime which preservesit, and thus it is prepared 20 .

The following compositions 21 are recommended to smelt all ores whichthe heat of fire breaks up or melts only with difficulty. Of these, one is madefrom stones of the third order, which easily melt when thrown into hotfurnaces. They are crushed into pure white powder, and with half an uncia

19 Sal artificiosus. These are a sort of stock fluxes. Such mixtures are common in allold assay books, from the Probierbuchlin to later than John Cramer in 1737 (whose Latinlectures on Assaying were published in English under the title of " Elements of the Art ofAssaying Metals,” London, 1741). Cramer observes (p. 51) that: “ Artificers compose a“ great many fluxes with the above-mentioned salts and with the reductive ones; nay,“ some use as many different fluxes as there are different ores and metals ; all which, however,“ we think needless to describe. It is better to have explained a few of the simpler ones,“ which serve for all the others, and are very easily prepared, than to tire the reader with“ confused compositions : and this chiefly because unskilled artificers sometimes attempt“ to obtain with many ingredients of the same nature heaped up beyond measure, and with“ much labour, though not more properly and more securely, what might have been easily“ effected, with one only and the same ingredient, thus increasing the number, not at all“ the virtue of the things employed. Nevertheless, if anyone loves variety, he may, according“ to the proportions and cautions above prescribed, at his will chuse among the simpler kinds“ such as will best suit his purpose, and compose a variety of fluxes with them.”

20 This operation apparently results in a coating to prevent the deflagration of thesaltpetre—in fact, it might be permitted to translate infiammatur “ deflagrate,” instead ofkindle.

21 The results which would follow from the use of these “ fluxes ” would obviouslydepend upon the ore treated. They can all conceivably be successful. Of these, the firstis the lead-glass of the German assayers—a flux much emphasized by all old authorities,