446 Mr. R. Phillips on the [June, 



pervade the conductor with facility, but it will constitute a cur- 

 rent as soon as the circuit does not oppose the obstacle of very 

 considerable isolation. It is easy to perceive that the quantity 

 of electricity developed by this continual excitation which exists 

 in the circuit, ought to be so much the greater as the circuit is a 

 more perfect conductor. Thus the thermoelectric circuit sup- 

 plies an incomparably greater quantity of electricity than any 

 other circuit which has as yet been invented. If by other circuits 

 water, the acids, and the alkalies, have been successively decom- 

 posed, it is not beyond the limits of probability, that by means 

 of a new circuit, we shall be able to decompose even the metals, 

 and thus complete that great change in chemistry which com- 

 menced with the pile of Volta. 



Article VIII. 



Aria/i/sis of the Native Sulphate of Iron and Alumina. 

 By R. Phillips, FRS. L. and E. &c. 



Until after I had completed the analysis of this substance, 

 I was not aware that it had been noticed in any work on mine- 

 ralogy : I find, however, that it has been described in the 24th 

 number, p. 97, of Mr. Sowerby's Exotic Mineralogy ; the speci- 

 men mentioned and figured in this work under the name, of sul- 

 phate of iron and argilla, is stated to be from Bacherstolln, in 

 Schmolnir. Mr. Sowerby mentions that it seems to have been 

 mistaken for native alum, but he justly observes that it differs 

 from alum in containing no alkali, and that the solution yields it 

 upon the addition of potash. 



The salt which I subjected to examination originates from the 

 decomposition of iron pyrites in slate-clay. It was presented to 

 me by Charles Macintosh, Esq. and is plentifully met with in 

 the slate clay of the deserted coal mines of Hurlet and Campsie, 

 which as well known is employed for the double purpose of pre- 

 paring alum and sulphate of iron. 



The sulphate of iron and alumina exists in the state of soft 

 delicate fibres, easily separable from each other; it is colourless, 

 and its lustre is silky, and it resembles asbestus in appearance. 

 It is so extremely light that 100 grains of the crystals occupy a 

 space equal to that of an ounce and a quarter of water. By expo- 

 sure to moist air, the iron is converted into peroxide, and the 

 crystals become yellowish-brown. It is readily soluble in water, 

 and the solution, as above stated, readily yields crystals of alum 

 on the addition of the salts of potash or ammonia. By sponta- 

 neous evaporation, crystals of common sulphate of iron are 

 obtained, and the sulphate of alumina remains in solution ; this 



