1872.] Capt. W. A. Ross on Pyrology, or Fire Analysis. 459 



changing its position in the pyrocone to that of a, fig. 1, at present called 

 the " oxidizing flame," the yellow precipitate immediately and copiously 

 reappears ; but there is no visible mark or signification by which the 

 operator can thus judge of the quantity of silver oxide added. When, how- 

 ever, this amounts to 5 per cent, of the whole glass, and the latter, rendered 

 diaphanous by the first position, is suddenly and momentarily brought into 

 the second one indicated above, or, better, to just the tip of the blue, from 

 whence, however, it must be instantaneously removed, a very remarkable 

 and very beautiful appearance results. It is that of an almost perfect imi- 

 tation of a pearl, produced apparently by the reduction of the oxide near 

 the surface to the metallic state, while a vitreous glaze or gloss is still re- 

 tained upon the surface. 



43. This, then, may be called the first standard of silver for ores con- 

 taining that oxide up to 5 per cent., though of course it may be used for 

 richer ones ; but the following method is more rapid for a rich ore, pro- 

 vided there are no chromatic oxides present to interfere with the clearness 

 of the glass. 



44. Second, for rich argentiferous ores. If we continue adding oxide of 

 silver to a weighed P glass, and dissolving it carefully as at 3, fig. 1, we shall 

 find the glass remain diaphanous until 20 per cent, of the oxide has been 

 added, when the yellow creamy precipitate again begins to appear, causing, 

 for rich ores, 20 to be the standard of silver. Of course, in calculating 

 results from these " standards,'' the ratio deducible from them must be of 

 the inverse kind ; that is, for instance, if we find an argentiferous ore re- 

 quires to be added to the extent of 40 per cent, in order to produce the 

 yellow precipitate in a P. P. as at 3, fig. 1, or just double the quantity of 

 the pure oxide of silver to effect the same result, we take the proportion of 

 Ag as just half of purity, or 50 per cent. 



Mercury and the Volatilizable Metals in P. 



45. If these oxides are taken upon the hot glass, and the mass inserted 

 into a good H. P. as in fig. 4, they are neither volatilized nor dissolved. 

 The volatile oxides under such conditions form part of the metallic-looking 

 crust or film, which is invariably formed over the surface, and can thus be 

 added in large quantity with a very trifling loss. If the mass be now 

 treated with a P. P. as at 3, fig. 1, these oxides are rapidly dissolved, all of 

 them bestowing on the P glass a brilliant golden yellow, especially arsenic 

 acid, by which a glass is thus produced quite equalling in appearance the 

 finest topaz. 



46. If" this glass be now returned to an O. P., as at a, fig. 1, the oxide is 

 immediately precipitated with a dim, and often an opaque grey or grey-black 

 appearance ; and although mercuric oxide (for instance) is usually presumed 

 to be of so volatile a nature that its reactions are not given in blowpipe 

 tables, this mercurial oxide is so difficult to volatilize that the strongest 

 O. P. will not clear the P bead from it, but only burn both slowlv away. 



