460 BOOK X. 



pound and is stirred; afterward it is poured into another crucible, first 

 warmed and lined with tallow, and then violently shaken. The rest is per- 

 formed according to the process I have already explained. 



Gold may be parted without injury from silver goblets and from other 

 gilt vessels and articles 22 , by means of a powder, which consists of one part of 

 sal-ammoniac and half a part of sulphur. The gilt goblet or other article 

 is smeared with oil, and the powder is dusted on ; the article is seized in the 

 hand, or with tongs, and is carried to the fire and sharply tapped, and by this 

 means the gold falls into water in vessels placed underneath, while the 

 goblet remains uninjured. 



' kind are, all blackening, flying, penetrating, and burned things ; as is vitriol, sal-armoniac, 

 ' flos aeris (copper oxide scales) and the ancient fictile stone (earthen pots), and a very small 

 ' quantity, or nothing, of sulphur, and urine with like acute and penetrating things. All 

 ' these are impasted with urine and spread upon thin plates of that body which you intend 

 ' shall be examined by this way of probation. Then the said plates must be laid upon a 

 ' grate of iron included in an earthen vessel, yet so as one touch not the other that the virtue 

 ' of the fire may have free and equal access to them. Thus the whole must be kept in fire 

 ' in a strong earthen vessel for the space of three days. But here great caution is required 

 ' that the plates may be kept but not melt." 



Albertus Magnus (1205-1280) De Mineralibus et Rebus MetaUicis, Lib. IV, describes 

 the process as follows : " But when gold is to be purified an earthen vessel is made like a 

 ' cucurbit or dish, and upon it is placed a similar vessel ; and they are luted together with 

 ' the tenacious lute called by alchemists the lute of wisdom. In the upper vessel there are 

 ' numerous holes by which vapour and smoke may escape ; afterwards the gold in the form 

 ' of short thin leaves is arranged in the vessel, the leaves being covered consecutively with a 

 ' mixture obtained by mixing together soot, salt, and brick dust ; and the whole is strongly 

 ' heated until the gold becomes perfectly pure and the base substances with which it was 

 ' mixed are consumed." It will be noted that salt is the basis of all these cement com- 

 pounds. We may also add that those of Biringuccio and all other writers prior to Agricola 

 were of the same kind, our author being the first to mention those with nitre. 



PARTING WITH NITRIC ACID. The first mention of nitric acid is in connection with 

 this purpose, and, therefore, the early history of this reagent becomes the history of the 

 process. Mineral acids of any kind were unknown to the Greeks or Romans. The works 

 of the Alchemists and others from the I2th to the I5th Centuries, have been well searched 

 by chemical historians for indications of knowledge of the mineral acids, and many of such 

 suspected indications are of very doubtful order. In any event, study of the Alchemists 

 for the roots of chemistry is fraught with the greatest difficulty, for not only is there the 

 large ratio of fraud which characterised their operations, but there is even the much larger 

 field of fraud which characterised the authorship and dates of writing attributed to various 

 members of the cult. The mention of saltpetre by Roger Bacon (1214 94), and Albertus 

 Magnus (1205-80), have caused some strain to read a knowledge of mineral acids into their 

 works, but with doubtful result. Further, the Monk Theophilus (1150-1200) is supposed 

 to have mentioned products which would be mineral acids, but by the most careful scrutiny 

 of that work we have found nothing to justify such an assertion, and it is of importance to 

 note that as Theophilus was a most accomplished gold and silver worker, his failure to men- 

 tion it is at least evidence that the process was not generally known. The transcribed manu- 

 scripts and later editions of such authors are often altered to bring them " up-to-date." 

 The first mention is in the work attributed to Geber, as stated above, of date prior to the 

 I4th Century. The following passage from his De Inventione Veritatis (Nuremberg edition, 

 1545, p. 182) is of interest : " First take one libra of vitriol of Cyprus and one-half libra 

 " of saltpetre and one-quarter of alum of Jameni, extract the aqua with the redness of the 

 " alembic for it is very solvative and use as in the foregoing chapters. This can be made 

 " acute if in it you dissolve a quarter of sal-ammoniac, which dissolves gold, sulphur, and 

 " silver." Distilling vitriol, saltpetre and alum would produce nitric acid. The addition of 

 sal-ammoniac would make aqua regia; Geber used this solvent water probably without 

 being made " more acute " to dissolve silver, and he crystallized out silver nitrate. It 



22 There were three methods of gilding practised in the Middle Ages the first by 

 hammering on gold leaf ; the second by laying a thin plate of gold on a thicker plate of silver, 

 expanding both together, and fabricating the articles out of the sheets thus prepared ; and 

 the third by coating over the article with gold amalgam, and subsequently driving off the 

 mercury by heat. Copper and iron objects were silver-plated by immersing them in molten 

 silver after coating with sal-ammoniac or borax. Tinning was done in the same way. 



