187:2.] Capt. W. A. Ross on Pyrology, or Fire Analysis. 461 



As an example, it took 57" 1 mgrs. of PbO to azurize a green Ca pyrites 

 P bead of 100 mgrs. 



PbO S per cent. 



Then 24 : 15 :: 57*1 =35*6 Sulphur. 

 Cu 



24 : 16:: 57-1 =38-0 Copper. 

 Therefore the oxide of iron = 26 '4 Iron. 



This is not very wide of the actual composition of Cu pyrites as decided 

 by chemical analysis, which is sulphur 34'9, copper 34*6, iron 30*5. The 

 specimen treated was a rich one from Freiberg in Saxony *. 



52. With rich ores, as the red oxide, the method (paragraph 49) is so 

 delicate, that an assay roasted through platinum foil gave 4 mgrs. more in 

 the hundred than it did unroasted. The best and safest plau is to have an 

 azure P- glass coloured with 5 per cent of CuO as a pattern, and place the 

 assay alongside of it on a sheet of white paper. 



Titanium and Tin in P. 



53. A diaphanous P glass having either of these oxides dissolved in it 

 will, after being held a considerable time as at 3, fig. 1, show (apparently) 

 crystals, yellow with Ti, aud white with Sn, produced in it. This result 

 cannot be effected with the mouth, but only with a table pyrogene f . 



Alumina and Silica in P. 



54. Berzelius proposes (page 86) to estimate silica pyrognostically in a 

 mineral thus : — " Every substance of an earthy or mineral nature, which 

 melts with soda with effervescence into a transparent glass which remains 

 transparent on cooling, is either silica or a silicate in which the oxygen of 

 the silica is at least double the quantity of that of the base." This in- 

 genious discovery, which is strictly correct in cases where it is applicable, 

 and in such cases, therefore, most useful, is unfortunately inapplicable to 

 those silicates in which the estimation of the silica is of the most impor- 

 tance. The so-called "alkaline earths," especially Lime, will not permit 

 silica, though combined in any proportion, to yield a bead with soda trans- 

 parent on cooling, and they seem also to prevent or cancel effervescence in 

 the same. 



55. After many comparatively futile attempts to separate and estimate 



* Another mode of procedure with sulphides is to carefully add the roasted ore 

 (which, by a method of roasting to be hereafter described, invariably loses just 17 per cent.) 

 atom by atom to the P bead in a P.P. (when the CuO blue reaction will first appear) 

 until the FeS begins to interfere with it ; then deduct from the large amount of copper 

 t jus indicated the sulphur and iron as determined by roasting and protoxide of lead. 



f Such as are sold at Freiberg by " Herr Bcrgmechanikus Lingke," manufacturer 

 to the Royal University of that place : vide Plattner's 1 Probirkunst mit dem Lothrohre,' 

 vierte Auflage (Leipzig, 1865), p. 32, note. 



