458 Capt. W. A. Ross on Pyrology, or Fire Analysis. [June 20, 



appearance, which the application of a P. P. (as at 3, fig. 1) will soon re- 

 move, the bead then appearing not merely diaphanous, but highly refractive. 

 If this brilliant auriferous glass be now treated with a good H. P., the white 

 metallic-looking film referred to in paragraph 15 is formed, with a slight 

 but distinct shade of yellow like pinchbeck, which is apparently due to the 

 gold in solution ; and this bead may thus be made alternately diaphanous 

 and metallic -looking as often as is desired. 



38. If the auriferous transparent bead be carefully kept for some time 

 about half an inch, from the point of the whole pyrocone, or two inches from 

 the blue, as at 2, fig. 1, a beautiful shade of bluish rose-colour flushes over 

 it just as it is becoming cold*; and the production of this tint, which cannot 

 be confounded by the dullest observer with the red violet of cobalt, or the 

 amethystine tinge of titanic acid or manganese, is an excellent test of the 

 skill of the operator, as well as of the delicacy of the pyroconical reactions 

 in this flux, for a hair's breadth too far towards (3, fig. 1) will cause the 

 glass to be diaphanous and colourless on cooling ; while a corresponding 

 error in the other direction towards 1 will, as has been mentioned, produce 

 a muddy appearance. 



39. Gold-leaf is more rapidly dissolved, and the above reactions more 

 easily produced in a glass of phosphate of lime, which appears to be, under 

 pyrological conditions, a more powerful solvent of metallic oxides than any 

 other known flux. It will be afterwards described ; but it has the disad- 

 vantage in analysis, referred to in paragraph 32, of being a salt. 



40. The ruby colour bestowed by gold upon glass and fluxes would 

 thus appear, by the experiment above detailed, to be due to an exact 

 amount of oxidation. The oxides of tin and antimony, added with it to 

 colour glass under the name of " purple of Cassius " &c, seem not to have 

 any thing to do with the production of the colour f. 



Silver. 



41. The most infinitesimal trace of the oxide, or of a salt of silver, added 

 to a bead of P, gives a copious yellow precipitate like cream, accompanied 

 at first, if the bead be held in a P. P., as at 2 or 3, fig. \> by a very beau- 

 tiful but very transient rose-colour. This is such a delicate reaction for 

 silver, that it will be at once obtained from most galenas ; and although 

 thus a most important test qualitatively, is too fine to admit of being used 

 as a quantitative standard for the estimation of rich ores. 



42. There are two ways of effecting this. First, for an ore supposed to 

 contain only a small percentage of silver. If the slightly argentiferous 

 glass be retained in the position 3, fig. 1, the yellow precipitate soon dis- 

 appears, and the glass becomes clear, highly refractive, and brilliant. On 



* The addition of fresh P at this stage brings out this beautiful reaction still more 

 decidedly. 



f Ko metal, not even gold, has any tendency to alloy the platinum-wire in this flux 

 when kept under a P.P. [Phosphofiuate of lime gives with gold oxide a bead as blue 

 and brilliant as a sapphire. — September 14th, 1872.] 



