1872.] Capt. W. A. Ross on Pyrology, or Fire Analysis. 4o7 



quence of its use in therapeutics, than microcosmic salt can he. It is used 

 hy simply clipping the red-hot platinum-wire loop and the glass, of whatever 

 description, formed upon it into the bottle, when a fresh supply of phos- 

 phoric acid adheres to the hot bead, without the supply in the bottle being 

 at all adulterated. 



34. That the metaphosphate of soda does not, when heated, exert upon 

 substances added to it the reactions of an acid, unless the basic soda be 

 displaced by another base for which the acid possesses a greater attraction, 

 must be evident to an ordinary chemist; and there would appear to be few 

 substances for which phosphoric acid has a greater attraction than it has 

 for soda ; in fact, the most valuable pyrognostic reactions prima facie of the 

 acid upon substances have been lost to operators precisely because the salt 

 it forms with soda fails to give us those acid reactions, as follows : — The 

 acid effervesces violently with all carbonates, and with some of the metallic 

 oxides, the salt does nothing of the sort ; and the necessity felt by many 

 mineralogists and geologists of carrying about in their pockets a phial of the 

 unpleasant and dangerous hydrochloric or nitric acid is thus at once obviated. 



35. The acid used to dissolve cobalt oxide in any considerable proportion 

 is blue hot, but assumes on cooling a magnificent red-violet colour*, to which 

 the modern word " magenta " is partly applicable. When soda or potash 

 is applied to this glass in sufficient proportion (about 17 percent.) to form 

 the metaphosphate of those bases, the glass remains blue, and a standard 

 of alkali for purposes of calculation is thus evidently obtained. But as 

 cobalt oxide produces with this flux many shades of colour according to the 

 quantity in which it is added, from a pale and scarcely perceptible pink to 

 the deep crimson-violet above mentioned, and as these degrees of red are 

 exactly azurizedf by a corresponding strength or quantity of the alkali 

 added, it is plain chat a kind of chromatic scale or table of colours might 

 thus be made, of great use in the quantitative measurement of alkalies on 

 the one hand, or of cobalt oxide on the other, instead of the unvarying 

 "blue " which we find opposite oxide of cobalt in all blowpipe tables. 



36. Instead, therefore, of superfluously multiplying illustrations of the 

 difference between the reactions of the pure acid used as a flux and of the 

 assumed " free acid " in microcosmic salt, it will be better to give here in 

 slight detail some of the more important of the former with various 

 oxides. 



Gold. 



37. Is dissolved and oxidized by this flux in an O. P. (as at a, fig. 1), 

 when added in minute portions of the leaf — a fact which suggests that P 

 under these conditions is more powerful as a solvent than any one of the 

 mineral acids. As stated in paragraph 26, the position (a, fig. 1) will pre- 

 cipitate the dissolved gold oxide, rendering the bead of a dirty or muddy 



* Discovered by the writer on 12th July, 1869. 



t Lithia and its salts will not apparently azurize this cobaltine glass, but afford with 

 it a very pretty purple violet colour. 



