^nalyfis of the Sydney Earth, yg \ 



and tht fire was continued till a dry mafs remained. 400 grains of the acid were again 

 poured in, and diftiljedas before. Upon the dry mafs boiling water was poured, and the 

 whole was then emptied on a filter, and edulcorated. The refiduum, after a red heat, 

 weighed 87.75 grains, and confided of filiceous earth, mixed with fome mica, and with 

 particles of plumbago. 



B. The filtrated folution, by ammoniac, afforded a precipitate, which weighed g.50 

 grains ; and, being examined, as in the former experiment, yielded 6.50 grains of alumine, 

 and 3 grains of oxide of iron. 



The plumbago was feparated from the filiceous matter, in the manner already defcribed, 

 and amounted to about 10 grains. 

 ]3y this analyfis I obtained. 



Grains. 

 Silica and mica - - 77-75 



Alumine - - - 6.50 



Oxide of iron - - ■ 3 



Plumbago - - - 10 



97.25 



It appears therefore that the Sydneian earth, when treated with fulpliuric acid, is capa- 

 ble of being for the greater part decompofed ; and Mr. Wedgwood probably did not fuc- 

 ceed, becaufe his procefs was in fome refpe£t different, or that the diflillation was not 

 fufhciently repeated. 



1 have not thought it necefTary to be more circumftantial in the account of this fecond 

 analyfis, as the operations were fimilar to thofe of the former. 



SECT. IV. 



THESE experiments prove, that the earthy fubftance called Sydnela, or terra au/Jralisy 

 confifts of filiceous earth, alumine, oxide of iron, and black lead or graphite. 



The prefence of the latter appears to be accidental, and it probably was mixed with the 

 other fubflances at the time when they were tranfported, and depofited, by means of wa- 

 ter ; for this appears evidently to have been the cafe, from the general characters of this 

 mixed earthy fubftance. 



The quartz and mica, which are fo vifible, indicate a granitic origin ; and the foft white 

 earth has probably been formed by a decompofition of feldt fpar, fuch as is to be fecn in 

 many places, and particularly at St. Stephen's in Cornwall. The granitic fand which co- 

 vers the borders of the Mer de Glace-, at Chamouni, in Savoy, alfo much refembles the 

 ttrra aiifiralis, excepting that the feldt fpar is not in a ftate of decompofition ; in fhort, 

 the general afpeft, and the analyfis, concur to prove, that the Sydneia has been formed by 

 the difintegration and decompofition of granite, or gneifs. 



Mr. Wedgwood's experiments are fo circumftantial, that had I only examined the earth ' 

 laft brought to England, I (hould have fuppofed, with Mr. Nicholfon, that I had operated 

 on a different fubftance ; but, as I had an opportunity to examine, by analyfis, a portion of. 

 the fame earth on which Mr. Wedgwood made his experiments, and as I received it from 



Si* 



