1818.] Scientific Intelligence. 463 



pitated by ammonia and separated by the filter, I saturated the 

 liquid with nitric acid and precipitated the sulphuric acid by 

 nitrate of barytes. By this mode of analysis 1 found that the 

 weight of sulphuric acid in the salt was twice as great as that of 

 the peroxide of iron. Kow an atom of peroxide of iron weighs 

 10, and an atom of sulphuric acid 5. Hence it is evident that 

 this salt is composed of four atoms of sulphuric acid muted to 

 one atom of peroxide of iron ; or it is a perquadrisulphate of 

 iron. The very slow solubility in water of a salt containing so 

 much sulphuric acid is remarkable. It is curious, likewise, that 

 no decomposition of it is effected either by water or alcohol. It 

 is obvious from this, that the whole of the acid is united to the 

 peroxide of iron by a considerable affinity. 



XII. Plasticity of Clay ascribed to the Presence of Water. 



The singular property of argillaceous substances, in which 

 originate the occupations of the potter and porcelain manufac- 

 turer, that of forming a paste with water susceptible of being 

 moulded to, and preserving any destined form, is usually ascribed 

 to aluminous earth, but, in my opinion, very erroneously. 



It is well known, I believe, that alumina, whether native or 

 artificial, however minutely divided, does not possess the cha- 

 racter above alluded to, while in an uncombined state : that it 

 acquires it by solution in an acid and precipitation, and that if 

 the precipitate be deprived of the water in it contained, it 

 resumes its pristine intractability, if I may be allowed the ex- 

 pression. 



Does it not seem, therefore, that this valuable peculiarity 

 ■arises from the presence of hydrate of alumina in clays, &c. ? 



PHIL0-CHEM1CUS LoNDINENSIS. 



XIII. Notice respecting the Discovery of Pearl Sinter. 

 By Dr. Clarke. 



An English traveller of St. John's College, Cambridge, Mr. 

 Hastings Robinson, lately arrived in that University from his 

 travels in Italy ; bringing to the Professor of Mineralogy some 

 fine specimens of the curious hydrate of silica, commonly called 

 pearl-sinter, from Professor Santi, of Pisa ; accompanied by a 

 written statement of the manner in which this mineral was origi- 

 nally discovered by Professor Santi ; who published an account 

 of it in his Travels, under the name of amiatiti ; and also of the 

 reprehensible conduct of Dr. W. Thomson, of Naples, who 

 claimed the discovery as his own, and gave the mineral the name 

 of Jiorite. We shall insert an extract from Professor Santi's 

 letter to Mr. Robinson, in the original Italian : at the same time 

 expressing a hope that as the only effectual method of doing 

 justice to Professor Santi, his own name may be bestowed on 

 the mineral ; and that it may be henceforth called by no other 

 name than Santitile. 



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