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BOOK X.

As great expense is incurred in parting the metals by the methods thatI have explained, as night vigils are necessary when aqua valens is made,and as generally much labour and great pains have to be expended on thismatter, other methods for parting have been invented by clever men, whichare less costly, less laborious, and in which there is less loss if through care-lessness an error is made. There are three methods, the first performed withsulphur, the second with antimony, the third by means of some compoundwhich consists of these or other ingredients.

In the first method , 16 the silver containing some gold is melted in acrucible and made into granules. For every libra of granules, there is takena sixth of a libra and a sicilicus of sulphur (not exposed to the fire) ; this,when crushed, is sprinkled over the moistened granules, and then they are putinto a new earthen pot of the capacity of four sextant, or into several of themif there is an abundance of granules. The pot, having been filled, is covered,with an earthen lid and smeared over, and placed within a circle of fire set oneand a half feet distant from the pot on all sides, in order that the sulphuradded to the silver should not be distilled when melted. The pot is opened,

16 The object of this treatment with sulphur and copper is to separate a considerableportion of silver from low-grade bullion (i.e., silver containing some gold), in preparationfor final treatment of the richer gold-silver alloy with nitric acid. Silver sulphide is createdby adding sulphur, and is drawn off in a silver-copper regulus. After the first sentence, theauthor uses silver alone where he obviously means silver “ containing some gold,” and furtherhe speaks of the “ gold lump ” ( massula) where he likewise means a button containing a greatdeal of silver. For clarity we introduced the term “ regulus ” for the Latin mistura. Theoperation falls into six stages : a, granulation ; b, sulphurization of the granulated bullion ;c, melting to form a combination of the silver sulphide with copper into a regulus, an alloyof gold and silver settling out; d, repetition of the treatment to abstract further silver fromthe “ lump ; ” e, refining the “ lump ” with nitric acid ; /, recovery of the silver from theregulus by addition of lead, liquation and cupellation. j

The use of a “ circle of fire ” secures a low temperature that would neither volatilizethe sulphur nor melt the bullion. The amount of sulphur given is equal to a ratio of 48 partsbullion and 9 parts sulphur. We are not certain about the translation of the paragraph inrelation to the proportion of copper added to the granulated bullion ; because in givingdefinite quantities of copper to be added in the contingencies of various original coppercontents in the bullion, it would be expected that they were intended to produce somepositive ratio of copper and silver. However, the ratio as we understand the text in variouscases works out to irregular amounts, i.e., 48 parts of silver to 16, 12.6, 24, 20.5, 20.8, 17.8, or18 parts of copper. In order to obtain complete separation there should be sufficient sulphurto have formed a sulphide of the copper as well as of the silver, or else some of the copperand silver would come down metallic with the “ lump ”. The above ratio of copper added tothe sulphurized silver, in the first instance would give about 18 parts of copper and 9 partsof sulphur to 48 parts of silver. The copper would require 4.5 parts of sulphur to convertit into sulphide, and the silver about 7 parts, or a total of 11.5 parts required against 9 partsfurnished. It is plain, therefore, that insufficient sulphur is given. Further, the lithargewould probably take up some sulphur and throw down metallic lead into the “ lump ”•However, it is necessary that there should be some free metafiles to collect the gold, and,therefore, the separation could not be complete in one operation. In any event, on the aboveratios the “ gold lump ” from the first operation was pretty coppery, and contained somelead and probably a good deal of silver, because the copper would tend to desulphurize thelatter. The “ powder ” of glass-galls, salt, and litharge would render the mass more liquidand assist the “ gold lump ” to separate out.

The Roman silver sesterce, worth about 2| pence or 4.2 American cents, was no doubtused by Agricola merely to indicate an infinitesimal quantity. The test to be applied to theregulus by way of cupellation and parting of a sample with nitric acid, requires no explanation.The truth of the description as to determining whether the gold had settled out, by using achalked iron rod, can only be tested by actual experiment. It is probable, however, that thesulphur in the regulus would attack the iron and make it black. The re-melting of the regulus,if some gold remains in it, with copper and “ powder ” without more sulphur, would provideagain free metafiles to gather the remaining gold, and by desulphurizing some silver thisbutton would probably not be very pure.