of Mineral Substances. 2S1 



grains which may be estimated as charcoal and sulphur with 

 perhaps a little water. 



c. The residuum was mixed with 200 grains of sulphuric acid 

 and 400 of water, evaporated, and strongly ignited for half an 

 hour : it was then washed in water, and the filtered washings 

 were saturated with ammonia which threw down half a grain of 

 magnesia. 



d. The liquid was then evaporated to dryness, and the saline 

 mass heated till it no longer evolved fumes ; the dry salt weighed 

 4.5 grains, and had the properties of a mixture of sulphate and 

 muriate of potassa, the sulphate being to the muriate as 2 to 1. 

 [It is here not very evident how the muriate of potassa escaped 

 the action of the sulphuric acid, during the ignition in c] 



F. 



It appears from these experiments, 



1. That there is no bitumen, but only charcoal in this alum 

 ore, since neither bituminous oil, nor smoke, nor flame, are 

 produced during its distillation and combustion. 



2. That the sulphur is not combined with iron in the state of 

 pyrites, but in some peculiar combination with the carbonaceous 

 matter ; no pyrites is visible in the ore, and alcalis do not ex- 

 tract it, nor does muriatic acid evolve sulphuretted hydrogen. 



G. 



The estimation of the relative weights of the constituents of 

 this ore is therefore attended with difficulty ; the ingredients 

 that distinguish it as an alum ore, are alumina and sulphur. 

 Direct experiment gives the proportion of the former =160 in 

 1000. The proportion of sulphur may be deduced from the 

 result of process C, which affords 270 grains of sulphate of 

 baryta from one thousand of the ore. But of these 270 grains, 

 40 may be ascribed to the vitriol and gypsum, and 20 to the 

 sulphate of potassa (supposing 15 parts of that salt to be con- 

 tained in 1000 of the ore). We must therefore subtract 66 from 

 270, and there remain 204 parts of sulpliate of baryta, as the 

 equivalent of the sulphur of the ore. Tliesc 204 parts are equal 

 to 90.75 of sulphuric acid, (specific gravity 1.850) or =28.5 of 



Vol. Xir. U 



