1QA PHILOSOPHICAL TRANSACTIONS. [ANNO 17 98. 



carbonate of pot-ash, and a white precipitate was produced, which was collected 

 and edulcorated. This, when digested with diluted sulphuric acid, was dissolved; 

 and the superfluous acid being driven off by heat, boiling water was poured on the 

 residuum, which completely dissolved it. To this solution some drops of lixivium 

 of pot-ash were added, and by repeated evaporations the whole formed crystals of 

 alum. From the above experiment it appeared, that the muriatic acid had only 

 dissolved some alumina and iron ; but, in order to satisfy myself more completely 

 in respect to the component parts of this substance, I made the following analysis. 

 Analysis. — A. 400 grs. were put into a glass retort, which was then made red-hot 

 during half an hour. Some water came over, and the earth afterwards weighed 

 380.80 grs., so that the loss amounted to 1 9.20 grs. The greater part of this loss 

 was occasioned by the dissipation of the water imbibed by the earth; to which 

 must be added, the loss of weight caused by the combustion of a small portion of 

 vegetable matter. 



b. The 380.80 grs. were rubbed to a fine powder, and being put into a glass 

 retort, 1470 grs. of pure concentrated sulphuric acid were added. The retort was 

 then placed in a small reverberatory, and the fire was gradually increased, till the 

 acid was distilled over: it was then poured back on the matter in the retort, and 

 distilled as before, till a mass nearly dry remained. On this, boiling distilled water 

 was repeatedly poured, till it no longer changed the colour of litmus paper, and 

 was devoid of taste. The undissolved portion was then dried, and made red-hot; 

 after which it weighed 28 1 grs. 



c. I now mixed the 281 grs. with 300 grs. of dry carbonate of pot-ash, and ex- 

 posed the mixture to a strong read heat, in a silver crucible, during 4 hours. The 

 mass was loose, and of a greyish white: it was softened with water, and being put 

 into a retort, sulphuric acid was added to a considerable excess. The whole was 

 then distilled to dryness, and when a sufficient quantity of boiling water had been 

 added, it was poured on a filter, and the residuum was well washed; it was then 

 made red-hot, and afterwards weighed 274.75 grs. 



d. The solutions of b and c were added together, and were much reduced by 

 evaporation. Pure ammonia was then employed to saturate the acid, and a copious 

 loose precipitate, of a pale yellowish colour, was produced; which, collected, edul- 

 corated, and made red-hot, weighed 103.70 grs. — e. The filtrated liquor of d was 

 again evaporated, and carbonate of pot-ash being added, a slight precipitation of 

 earthy matter took place; which, by the test of sulphuric acid proved to be some 

 alumina which had not been precipitated in the former experiment: this weighed 

 1.20 grs. — f. The 103.70 grs. of d were completely dissolved when digested with 

 nitric acid, excepting a small residuum of siliceous earth, which weighed O.gOgrs. — 

 g. The nitric solution was evaporated to dryness, and a 2d portion of the same acid 

 was added, and in like manner evaporated. The residuum was then made red-hot, 

 and digested with diluted nitric acid, which left a considerable portion of red oxide 

 of iron. The solution was again evaporated, and the residuum, being treated as 



