Free Remarks on Mr, Gresnough's Geological Map, 379 



an excess of prussiate, although the latter did not, however, cause 

 any precipitate in the liquor which had given the white precipi- 

 tate. The yellow colour of prussiate of zircon explains how 

 Klaproth imagined that he had discovered nickel in zircon, be- 

 cause he obtained a green precipitate on mixing with the prus- 

 siate of potash a solution of zircon which contained a little iron. 



The hvdrochlorate of zircon does not become violet when a 

 little zinc is added, vvhich is the case with hvdrochlorate of ti- 

 tanium. 



The two hvdrochlorates have an excessively astringent taste, 

 and both precipitate gelatine; which proves that they have much 

 more affinity for animal matters than the salts of yttria, of g!u- 

 cine, and of alumine, the taste of which is sweet, and only slightly 

 astringent. 



The two h3drochlorates are completely decomposed by a red 

 heat ; they lose their acid, and their base remains in a state of 

 purity; the zircon is perfectly white ; the peroxide of titanium 

 is of a yellowish gray. 



Lastlv: The hydrates of titanium and zircon heated in a small 

 glass capsule above the flame of alcohol blacken, and then be- 

 come incandescent as if they experienced a combustion. The 

 ;circon is demi-vitrified, and of the purest white when exempt 

 from iron ; when it contains iron, it is of a greenish hue. The 

 oxide of titanium is of a gray yellow. 



M. Chevrcul intends to publish in a second memoir the pro- 

 portion of the elements of silicate and zirconate of potash. He 

 will determine the composition of several salts of zircon, and will 

 investigate, whether the colour of prussiate of zircon may not bs 

 owing to some foreign substances, perhaps to traces of peroxide 

 of titanium. 



LXV. Free Remarks on Mr. Greenough's Geological Map, 

 latcdy puldishrd under the Direction of the Geological Society 

 of London. By Mr. John Farey Senior y Mineral Surveyor, 



Letter I. 



To Mr. Tilloch. 



Sir, — Amongst the Readers on Geological Subjects, within 

 the last five Years, very higli exjiectations have been raised, by 

 several Writers (by tU'o in particular*), as to the vail superiority 

 which a Geological Map of England and Wales, which Mr. 



• Mr. Wm. Phillips, in July IRIG, in tlic Appendix to the 1st Edit, of his 

 *♦ Outlines of the Geology ot Enj^land, " p. 2'J, and in his 2d Edition of the 

 •ame date- ; and Dr. rittoii (anonymously) in Ftb. ISlS.iu the "Edinburgh 

 Jlcvicw," Vol. xix. p. 'S^Ci, sec P. M. Vol. 52, p. It 4, note. 



K k 2 - Grccnough 



