1872.] Capt. W. A. Ross on Pyrology, or Fire Analysis. 469 



82. It will be found that only a certain and normal, not an uncertain 

 and irregular degree of heat can thus be applied to substances which under 

 pyrological conditions combine with oxygen or are reduced to the metallic 

 state ; and therefore that oxidation on the one hand is as exactly regu- 

 lated as though it had been controlled by a balance, and that reduction 

 on the other hand need not be feared, except in the case of the very fusible 

 metals, as antimony or lead. For instance, copper pyrites roasted in this 

 way will be found to lose exactly 17 per cent, and no more, however long or 

 strongly the pyrocone has been applied. The same amount of sulphur is 

 thus driven off from "copper glance;" and there can therefore be little rea- 

 sonable doubt that 17 per cent, is the extent to which sulphur may be 

 dissipated from copper ores without fusing both together. 



Sublimation. 



83. This is better performed on such a platinum tray held by steel-legged 

 forceps than in the ordinary manner on charcoal or in a glass tube. By 

 mixing a little common rust or lime with arsenic or antimony, the most 

 timid operator need not fear injury to his platinum, which, however, it is far 

 better to spoil than to lose a single valuable reaction. The addition of iron 

 sesquioxide has another advantage ; for it will be observed that the anti- 

 monial oxide mixed with it is deposited on the upper steel leg of the forceps 

 unchanged as a white sublimate, but the arsenic oxide as an orange one, 

 in consequence, it is presumed, of the ability of the latter to carry up a 

 portion of the red iron oxide with it. This would appear to afford a valu- 

 able distinction between these two metals in toxicological cases, which even 

 Marsh's test does not give. 



84. If flour sulphur be treated in this way, and the upper leg of the 

 forceps be sufficiently high to be out of its blue flame, for of course it ignites, 

 the steel leg will not be found to have changed further than by being covered 

 with a yellow varnish, which is apparently distilled sulphur ; but if the leg 

 be plunged warm into water, it will appear white from the number of 

 bubbles caused by some chemical action upon it. If instead of sulphur 

 only, a mixture of sulphur and any inorganic substance containing nitrogen, 

 as gunpowder (only of course, for this purpose, that must be well watered 

 and ground into a paste), be used, we shall find the forceps apparently 

 unchanged; but after being plunged warm into water, the upper leg will 

 come out perfectly black. No bubbles will be observed through the lens, 

 but the leg, on drying, will be found covered with rust. 



85. This curious reaction is also produced when sulphur is thus subli- 

 mated in company with such minerals as emit an empyreumatic or nauseous 

 odour when heated in a matrass alone, as, e.g., stinkstone. Such minerals, 

 dissolved in a V glass, give also the nitrogenical reaction referred to in 

 paragraph 48 ; and one of such (a black mineral found at Mussoorie in 

 India, as hard as topaz, though consisting apparently only of silica, and 



