^S Anal'^is of the SyJtxy Earth. 



with two parts of foda, a colourlefs glafs was formed ; and, with four parts of the fame, It 

 was foluble in water, and produced liquor ftlicum : it was therefore pure filiceous earth. 



I. The filtrated liquor was faturated with ammoniac ; and, upon being heated, a few 

 brownifli flocculi were precipitated, which, when colle£led and dried, weighed 0.40 grain. 

 This precipitate was diflblved in muriatic acid, and was again precipitated by pruffiate of 

 potafli, in the ftate of Pruffian blue. 



The liquor from which the flocculi of iron had been feparated was then examined, by 

 adding carbonate of potalh, and, laftly, by being evaporated to drynefs ; but it no longer 

 afforded any earthy or metallic fubftance : fo that, by the procefs of detonation with nitre, 

 the 85.50 grains afforded 75.25 grains of pure filiceous earth, with 0.40 grain of iron ; and, 

 as the dark grey fubftance was deftroyed, excepting the 0.40 grain of iron above mentioned, 

 and as 9.85 grains of the original weight of ^5.50 grains were diffipated, there can be no 

 doubt but that this fubftance, amounting to 1O.25 grains, was carburet of iron or plumbago ; 

 efpecially as fome experiments which I purpofely made, on that from Kcfwick in Cum- 

 berland, were attended with fimilar refults. 



It is alfo evident, that thefe particles could not be eife/iglimmer, or micaceous iron, as 

 nitre has little or no efFeft on that fubftance, when projedted into a heated crucible. 



In a fubfequent experiment on the fame, the crucible was removed immediately after the 

 Jaft projection; and 1 then obferved that an efFervefcence, with a difengagement of carbonic 

 acid, took place, upon the addition of the muriatic acid, as is ufual when pure plumbago is 

 decompofed by nitre, and that lefs of the gelatinous matter was formed by evaporation. 



The caufe of this difference was evidently the duration of the red heat ; for, in the firft 

 inftance, the alkali developed by the decompofition of the nitre had time to unite with the 

 filiceous earth, fo as, when dilTolved, to form liquor ftlicum ; but, in the fecond experiment, 

 a portion of alkali remained combined with the carbonic acid, produced by the carbon of 

 the decompofed plumbago. 



The produce of 100 grains by this anaiyfis was, 



Silica 



{. 



D. 0.30 

 .H. 75.25 



Alumlne - - - F. 7.20 



Oxide of Iron - - E. 3.20 



Graphite or plumbago - I. 10.25 



Water - - A. 2.20 



98.40 



Mr, Wedgwood fays, that fulphuric acid cannot dilTolve the precipitated earth, and has 

 but Httlc eflFeft on the mixed fubftance, even when diftilled to drynefs ; but, from the pre- 

 ceding experiments, I had reafon to believe that the aluminous earth and Iron would be 

 feparated by reiterated diftUlatlon ; I therefore repeated the anaiyfis in the following man- 

 ner. ' 



Second Anaiyfis of the Sydneia, No, 2. 

 A. 100 grains of the earth were put into a glafs retort, upon which 400 grains of pure 

 concentrated fulphuric acid were poured. The retort was placed in a fmall reverberatory, 



and 



