136 Observations on the Purity of Standard Gold, 



attested by the Holy Scripture : we find it at such adegree 

 of perfection even in the time of Pliny *, that by means 

 of it the standard of gold was fixed at 21 carats, or 0*875, 

 at SI carats and 7-24ths (0888) up to 23 carats and 

 ll-32ds (0*973). In those days they must have assayed 

 in the dry way, first by separating from the gold the viler 

 metals by means of lead, and afterwards even the silver, 

 with sulphur or with the sulphurets f. 



They were also acquainted with the method of refining 

 and purifying gold in large quantities, by cementing or 

 burning it, as Strabo informs us, with an aluminous earth, 

 which by destroying the silver left the gold in a state of 

 purity. Pliny says that for this purpose they put the gold 

 on the fire in an earthen vessel, with treble its weight of 

 salt ; that it was afterwards again exposed to the fire with 

 two parts of salt and one of argillaceous sclustus: this would 

 surely effect the decomposition of the salt, and the volatili- 

 zation of the muriatic acid in a state of ignition and dry, 

 which would penetrate the substance of the gold, and wouid 

 separate the silver in the form of volatile muriate: this is 

 the object of the process of cementation among the mo- 

 derns J. But Agatharchides has transmitted to us a peculiar 

 method practised in the mines situated between the Nile aud 

 the shores of the Red Sea, in which we recognise the well- 

 known property of the muriatic acid in the separation of 

 silver. 



This writer says (if we may trust to the text being ac>- 

 curate) that in these places gold is inclosed in marble ; that 

 the miners burn or calcine the ore; that they break it with 



* The art of assaying was certainly very imperfect at these periods : un- 

 der the emperors the standard of gold and silver was still judged of by the 

 colour assut ed by the coin in the fire, and by the tint given to the touch- 

 stone on which the metal was rubbed. 



These methods, although practised by expert workmen, could yield but 

 very inaccurate results, which a variety of circumstances might influence ; 

 such as a complexity in the alloy, or a difFerent alloy, &c. 



Archimedes would not have applied the laws of specific gravity to the 

 determination of the standard value of king Micro's crown, if he had 

 known a better method. 



We know also that under the triumvirate of Mark Antony every street of 

 Rome erected a massive statue to Marcus Gratianus, who had discovered 

 and put in practice one of the processes of assaying mentioned above : this 

 denotes the infancy of an useful art, the first steps of which were strongly 

 encouraged as being intimately connected with public happiness. 



f By employing the alkaline sulphurets, the solution of gold might have 

 been effected: it is the metallic sulphurets, however, which ought to be used 

 in this process. 



* M. de Robilant, in his detail of the processes of the mint at Turin, 

 says that cementation is the mode of refining generally adopted at Venice, 

 Genoa, and at Florence, where they make gold seijuins almost entirely pure. 



hammers,. 



