ORIENTAL COMMERCE. 



[China, 



and one of copper ; the third with a mixture of two parts of copper to one 

 of silver; and the fourth with equal parts of the two; to which some add 

 a fifth set with copper only, an alloy which sometimes occurs, though much 

 more rarely than the others. If needles so low as three or four carats can 

 he of any use, it should seem to he only in the first set ; for in the others, 

 the proportion of copper being large, the differences in colour of different 

 sorts of copper itself, will be as great as those which result from very con- 

 siderable differences in the quantity of gold. When the copper is nearly 

 equal in quantity to the gold, very little can be judged by the colour of 

 the mass. 



The colours are best examined by means of strokes drawn with the 

 metals on a particular kind of stone, brought chiefly from Germany, and 

 called from this use a touchstone ; the best sort of which is of a deep black 

 colour, moderately hard, and of a smooth but not polished surface. If it is 

 too smooth, soft gold will not easily leave a mark upon it; and if rough, the 

 mark proves imperfect. If very hard, the frequent cleaning of it from the 

 marks, by rubbing it with tripoli, or a piece of charcoal wetted with water, 

 gives the surface too great a smoothness; and if very soft, it is liable to be 

 scratched in the cleaning. In want of the proper kind of stone, moderately 

 smooth pieces of flint are the best substitutes ; the more those approach in 

 colour to the other, the better. 



The piece of gold to be examined, being well cleaned in some con- 

 venient part of its surface, a stroke is to he made with it on the stone, and 

 another close by it, with such of the touch-needles as appear to come the 

 nearest to it in colour. If the colour of both upon the stone is exactly the 

 same, it is judged that the given mass is of the same fineness with the needle; 

 if different, other needles must be tried, till one is found which exactly cor- 

 responds with it. To do this readily, practice only can teach. 



In making the strokes, both the given piece and the needle of com- 

 parison are to be rubbed several times backwards and forwards upon the 

 stone, that the marks may be strong and full, not less than a quarter of an 

 inch long, and about the eighth or a tenth of an inch broad; both marks are 

 to be wetted before the examination of them, their colours being thus 

 rendered more distinct. A stroke which has been drawn some days, is never 

 to be compared with a fresh one, as the colour may have suffered an alteration 

 from the air, the line atoms left upon the touchstone l>eing much more sus- 

 ceptible of such alterations than the metal in the mass. If the piece is 

 supposed to be superficially heightened by art in its colour, that part of 

 it which the stroke is designed to be made with, should be previously ruhbed 

 on another part of the stone, or rather on a rougher kind of stone than the 

 common touchstones, that a fresh surface of the metal mav be exposed. 



