1824.] Examination of Brochantite by the Blowpipe. 243 



follow. His experiments were performed upon two or three 

 small crystals, the largest of which weighed about l-80th part of 

 a grain. The only substances he could detect in them are 

 alumina and fluoric acid. He also measured the refractive 

 power comparatively with that of wavellite, and found the index 

 of refraction to be 1*47, whilst that of wavellite is T52. He is, 

 therefore, of opinion that these crystals belong to a distinct 

 species, for which he proposes the name of Fluellite. He also 

 measured the crystals, and found 



(6, b') = 144° {b, b") = 109° (b, b) = 82. 



Hence the primitive form may be assumed to be a right 

 rhombic prism, the lateral planes of which are inclined to each 

 other at about 105°. 



I shall conclude this short paper by mentioning, that upon a 

 specimen from Mendip, near Churchill, Somersetshire, I have 

 found a white laminary substance which cleaves with great faci- 

 lity, and brilliant surfaces parallel to the lateral planes and 

 shorter diagonal of a rhombic prism of 102° 25', and thus differs 

 from sulphate of lead to which it bears a great resemblance, and 

 is very likely the substance, from the same locality analyzed by 

 Berzelius, a notice of which was inserted in the number of the 

 Annals of Philosophy for August last. I could find no cleavage 

 in the direction of the base. 



Examination of the preceding Mineral by the Blowpipe, 8$c. 



At Mr. Levy's request, I have examined the Brochantite by 

 the blowpipe, but the quantity which he could supply me with 

 was so very small, not exceeding two-tenths of a grain in all, 

 that I have been unable to obtain satisfactory information as to 

 the true composition of the mineral. The results, however, such 

 as they are, I lay before our readers. 



A minute crystal, not half the size of the smallest pin's head, 

 heated alone on charcoal, immediately lost its fine green colour, 

 and became dark brown, slightly inclining to a reddish hue, but 

 did not fuse. The heated particle was not attracted by the 

 magnet. Another particle cemented to the end of a fine platina 

 wire by alumina, in the manner recommended by Mr. Smithson, 

 fused readily, and alloyed with the platina. 



With soda on the platina wire, and in the oxidating jlume, the 

 assay gave a brown opaque globule, which was not perceptibly 

 altered in the redncingjlame. 



Wilh borax, in the oxidating flame, the assay gave a transpa- 

 rent, very deep green glass. When the dux was not in large 

 proportion to the assay, the globule appeared black, from the 

 intensity of the colour. In the interior flame the green colour 



r 2 



