Mr. D. Forbes on Phosphorite from Spain. 341 



not be accompanied by a change in its specific gravity, two ex- 

 periments were made upon fragments of the mineral, which, after 

 having had their specific gravity determined, were heated to 

 visible redness for some time, and, after cooling, a second deter- 

 mination of their specific gravity was made. In both cases a 

 somewhat higher result was obtained after ignition than before, 

 the exact numbers being as follows : — before ignition the specific 

 gravities of the specimens were 3'CO and 2*92, but after ignition 

 3*12 and 2*98 respectively. 



As the mineral was found to lose weight upon ignition 

 (amounting to 1*44 per cent.), the specific gravity of the mineral 

 after ignition was calculated from the weight of the mineral left 

 behind after heating, and not from the weight of the phosphorite 

 actually employed in the first instance, from which weight the 

 specific gravity of the unignited mineral had been calculated. 



It seems, however, not improbable that the increase of specific 

 gravity may really be due to the mineral becoming less porous, 

 or contracting, on losing the water (probably only hygroscopic), 

 and not connected at all with the phenomenon of phosphorescence. 

 Before the blowpipe the mineral behaves as follows : — A thin 

 fragment heated in the platinum-points remains unchanged, but 

 at a very strong heat becomes rounded off at the edges, and, 

 provided the mass operated upon is sufficiently small, ultimately 

 fuses with great difficulty to a milk-white enamel. During this 

 heating, in general no coloration of the outer flame can be per- 

 ceived; but if the fragment be moistened in strong sulphuric 

 acid and introduced into the point of the blue flame, a distinct 

 bluish-green colour, quickly passing over, is seen at the moment 

 of contact of the mineral with the flame. 



In both open and closed tubes some little moisture is observed ; 

 and if a rather larger amount be heated in a bulbed tube and the 

 evolved moisture tested, it will be found to feebly redden blue 

 litmus paper, and give a somewhat yellow colour to Brazil-wood 

 paper. 



When heated with carbonate of soda it fuses with effervescence, 

 part of the mass is absorbed by the charcoal, and a white resi- 

 duum is left upon the surface. 



Heated with borax-glass it dissolves to a transparent glass, 

 somewhat yellow when hot, but colourless after cooling — a change 

 no doubt owing to a small amount of iron present in the mineral 

 itself. The glass, if sufficiently saturated, becomes milk-white ; 

 and if supersaturated with the mineral, becomes opake. 



Phosphate of soda* dissolves the phosphorite with much more 



* Instead of using the microeosmic salt or phosphate of soda and am- 

 monia, I find it much better to use the anhydrous phosphate of soda left 

 behind on heating microeosmic salt until all water and ammonia are 

 evolved. The reactions in both cases are precisely similar. 



