[38]. The author ſpeaks here of ſuch as he obtained by precipitation from acids, but the native Terra Ponderosa aerata (ſee note at page [28]) has a ſpecific gravity of nearly 4, 338. W.
[39]. Opuſc. vol. i. p. 21, 398.
[40]. N. Acta Upſ. Vol. II. page 198.
[41]. Opuſc. chem. vol. I, page 23.
[42]. Opuſc. chem. vol. I, page 398.
[43]. Opuſc. chem. vol. II. p. 29, 373.
[44]. Profeſſor Bergman does not here ſeem to be ſufficiently aware of the difference between our Devonſhire pipe clay, and that which is uſed in the manufacture of porcelain. The former, in an open fire, burns to a blueiſh grey, or pidgeon colour; the latter remains white. The former ſeems to be the ſame as the Cologne and Maeſtricht pipe clay, of Cronſtedt, §78; the latter is a decayed Feldſpath, and conſequently, according to our author, (§ 130) contains magneſia. Our porcelain clay, likewiſe, has quartz, chryſtals, and mica mixed with it, parts of the granite which it originally compoſed. Before it is uſed the quartz is ſeparated, but the mica remains. I am indebted to my friend Mr. Watt for theſe obſervations. W.
[45]. I have taken the liberty to add this ſpecies upon our author’s own authority. See Bergman Diff. de Lithomarga, page 13.
[46]. N. Acta Upſal. vol. III, page 121.
[47]. Opuſc. vol. I, page 291, 292.