VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 2Q5 



before, again deposited some oxide of iron, much less in quantity than the former. 

 The whole of the oxide was then heated with wax in a porcelain crucible, was taken 

 up by a magnet, and weighed 26.50 grs. # 



h. The nitric solution of g was saturated with ammonia, and a loose white pre- 

 cipitate was formed; which edulcorated and made red-hot, weighed 76 grs. — 

 1. These 76 grs. were dissolved when digested with diluted sulphuric acid; and, 

 when the excess of acid had been expelled by heat, the saline mass was dissolved 

 in boiling water. To this solution I added some lixivium of pot-ash, and by 

 gradual and repeated evaporations, obtained the whole in regular octoedral crystals 

 of alum. 



k. The 274.75 grs. of c now alone remained to be examined. They appeared 

 to consist of siliceous earth, mixed with the dark grey shining particles already 

 mentioned; but, as I shall describe, in the following experiments, the process by 

 which these were separated, I shall now only say that they amounted to 7.50 grs. — 

 l. The earth with which the above-mentioned 



particles were mixed weighed 267-25 grs. This Grains, 



earth was white, and arid to the touch: when Pure siliceous earth or silica / £' ggSgJ 

 melted with 2 parts of soda, it formed a colour- Alumina / E * 1,2 ° 



less glass ; and with 4 parts of the same it dis- Qxide of iron _"" '. \ ' \ «■ £ 7 2 f 50 



solved in water, and formed a liquor silicum ; it Dark grey particles k. 7.50 



was therefore pure siliceous earth or silica. The Water and ve § etable matter A - WM 

 substance here examined was composed there- 358.55 



fore of the following ingredients. 



The foregoing analysis was repeated several times, and always with similar results; 

 excepting, that as I had taken the specimens from different parts of a large quan- 

 tity, I found that the proportions of the ingredients were not constantly the same: 

 that of the siliceous earth, for example, was sometimes greater, and the alumina 

 and iron proportion ably less. Some specimens were also nearly or totally destitute 

 of the dark grey shining particles; in short, every circumstance was such as might 

 be expected from a mixed substance, which, from the nature of its formation, cannot 

 have the ingredients in any fixed proportion*. As this substance agreed in its 

 general characters, for the greater part, with that described by Mr. Wedgwood, 

 and as it was indisputably brought from the same place, there appeared every reason 

 to believe that the nature of both was the same; but, to obviate as much as pos- 

 sible any doubt or objection, I determined to repeat the experiments, and the 

 analysis, on that portion which remained of the identical substance examined by 

 Mr. Wedgwood, and which from that period had been reserved by Sir Jos. Banks. 

 § 3. Analysis of the Sydneia, N° 2. — This substance, then consists of a white 



* The description given by Mr. Klaproth convinces me, that his experiments were made on a portion 

 of this substance. Also, when Mr. Haidinger was in London, I gave him some of this earth for his 

 collection j so that, whether Mr. Klaproth made his experiments on that which had been received by 

 Mr. Haidinger from Sir Jos. Banks, or from myself, it is not less certain that he operated on that which 

 might be regarded as the genuine Sydneia. — Orig. 



