456 PHILOSOPHICAL TRANSACTIONS. [aNNO I678. 



consisting of saltpetre reduced, most of the spirit of vitriol being gone with the 

 copper into the verditer. A dish full whereof being put into the other materials 

 for aquafortis, is redistilled, and makes a double water, almost twice as good as 

 that without it. 



I come next to the second way of refining, viz. by the test. This separates 

 all metals from silver, except gold, because they swim over it when they are all 

 melted together. The test is thus made: they have an iron mould of an oval 

 form, and 2 inches deep, with 3 arches of iron at bottom, set at equal dis- 

 tances, 2 fingers wide, if the great diameter of it be 14 inches long, and so 

 proportionably in greater or less tests. This cavity they fill with fine powder 

 of bone-ashes, moistened with lixivium made with soap-ashes. Some use cakes 

 of pot-ashes, or other ashes well cleansed, and so pressed well together with a 

 muller, that it becomes very close and smooth at the top. A cavity is left above 

 in the midst of it, to contain the melted silver; this cavity being longest in the 

 middle: for the bone-ashes come up parallel to 4;he circumference of the mould, 

 only a small channel left in that end which is most remote from the blast, for 

 the running off of the baser metals, and so is made to decline to the centre of 

 the test, where it is not above half an inch deep. The test thus made, is set 

 annealing 24 hours, and then it is set in a chimney a yard high, parallel almost 

 to the nose of a pair of large bellows ; then the silver is put in, which being 

 covered all over with billets of barked oak, the blast begins, and continues 

 strongly all the while. The lead purified from all silver, which they call the 

 soap of metals, is first put in, and melts down with the silver; then the lead 

 and copper swim at the top, and run over the test ; the motion the refiner helps 

 with a long rod of iron, drawn along the surface of the silver towards the fore- 

 mentioned slit, and often stirring all the metal, that the impurer may rise the 

 better : and by thus continuing, the separation is made in 2 or 3 hours. The 

 greatest part of the lead flies away in fumes. 



If the lead be gone before all the copper, the metal will rise in small red fiery 

 bubbles; and then they say it drives, and more lead must be added. The force 

 of the blast drives the upper metal to the lower side of the test, and promotes 

 its iTinning over. When the silver is fully refined, it looks like very pure 

 quicksilver; then they take off their fogs and let it cool. In the cooling, the 

 silver will frequently from the middle spring up in small rays, and fall down 

 again. If moist silver be put into that which is melted, it will spring into the 

 fire. A good test will serve two or three firings. As soon as the silver will 

 hold together, they take it out of the test, and beat it on an anvil into a round 

 figure, for the melting pot ; which being set in a wind furnace, surrounded with 

 coal, and covered with an iron cap, that no charcoal fall into it, it is then 



