1813.] Mineralogicul Observations. 345 



Exposure to air does not appear to be necessary, for the mix- 

 ture of the neutralized liquor "(Scot. 1.) and ammonia becomes 

 turbid in close vessels. 



If nitric acid be added to the neutralized liquor (Sect. I.) 

 previous to its being supersaturated with ammonia, the manga- 

 nese is not more speedily separated, and in some experiments 

 the nitric acid seemed rather to retard that effect. 



1 need scarcely mention, that in cases of analyses, if any 

 alumina, or calcareous earth, &c. should be suspected to have 

 become mixed with the precipitated oxide of manganese, they 

 may be readily separated by digestion in \ciy dilute nitric acid. 



If a mixture of the neutralized solution of manganese and 

 of green muriate of copper be supersaturated with ammonia, as 

 in Sect. 11., the manganese separates, as already described, the 

 copper remaining in tohition ; and if the liquor be evaporated 

 to drvness, the copper may be taken up and separated from the 

 oxide" of manganese by digesting the residuum in warm am- 

 monia. 1 am, dear Sir, 



Yours very sincerely, 



Charles Hatchett. 



Article IV. 



Mineralogical Observations. By Robert Jameson, Esq. F.R.S.E. 

 Regius" l'rofessor of Natural History in the University of 

 Edinburgh. 



The mineralogical investigations I have been engaged in for 

 some years past have enabled me to make several interesting 

 observations. The following short enumeration contains a few 

 of the most important of these: — 



1. That primitive rocks contain no mechanical depositcs, the 

 conglomerated rocks in gneiss and porphyry being entirely of a 

 chemical nature. 



2. That greywacke is always a pure chemical deposite, and 

 contains no mechanical intermixture. 



3. That felspar occurs more abundantly in nature than is 

 generally supposed, this mineral being one of the principal con- 

 stituent parts of granite, gneiss, clay slate, porphyry, sienite 

 terpentine, flinty slate, homstone', greywacke, transition s/ate t 

 striped jasper, aides! conglomerates, besides forming in some 

 degree the basis of most <>l the; primitive, transition, and floetz 

 trap rocks. 



I. That the vast beds of conglomerate which rest upon, and 



» 



