Miscellanies. 397 



gravity, and then compare the proportionate quantities in pyrochlore 

 from different localities, he will no doubt find that a proper investigation 

 of the character of specific gravity, like that of its chemical and its 

 crystallographic characters, will result in the complete identity of pyro- 

 chlore and microlite. 



It is very possible that the recent discovery of niohium and pelopium, 

 two new metals in the columbite of Bodenmais by Rose, may add new 

 interest to this columbate of lime from Chesterfield. 



Yours truly, J. E. Teschemacher. 



Boston, 1st March, 1845. 



2. Note on PseudomorpMsm ; by James D. Dana. — The following 

 fact with regard to the solution of silica, from the Report of the British 

 Association for 1840, (2d part, p. 125,) has an important bearing on 

 pseudomorphism, and especially on the principles discussed in the Jan- 

 uary number of this Journal, as well as other changes in which silica is 

 concerned. The experiments described were made by Mr. J. Jeffrys, 

 and expressly to ascertain the effect of water at a high temperature on 

 silica and siliceous minerals. A large boiler used for vitrifying brown 

 stone ware was employed, heated by four exterior furnaces, each six 

 feet long and five wide. Between each of the furnaces and the kiln a 

 deep pit was made, into which three feet of water was put, which was 

 renewable from without. 



" Some feldspathic and siliceous minerals were placed in the way 

 of the current, just inside of the kiln, and upon some of the arches a 

 few articles of ware were placed, that any action upon them might be 

 observed. Below a full red heat little effect was perceived, but at a 

 heat above that of fused cast iron a rapid solution of mineral matter 

 took place. This heat was continued ten hours. When the kiln was 

 opened, more than a hundred weight of mineral matter, though in a 

 very dense and refractory form, had been dissolved, and carried away in 

 the vapor. The wall was eaten away, and presented a rough, and 

 quite unglazed surface like loaf-sugar partially melted by water, or as 

 if eroded by some animal ; and nothing of the smooth glazed surface, 

 which invariably attends the action of alkali on a siliceous surface. 

 Some articles of ware in the hottest situations were partially eaten 

 through; but on the uppermost arch, where the heat was only a full 

 red, a curious phenomenon appeared. The articles there had receiv- 

 ed, exterior to their own brown gloss, and loosely encrusting it, a com- 

 plete frosted coat of silica, having the appearance of a candied surface. 

 It was manifestly a precipitation from the mineral vapor, and in fact a 

 hoar-frost of silica. There was probably from half an ounce to an ounce 

 on each vessel, and several pounds altogether were thus precipitated ; 



Vol. XLViii, No. 2.— Jan.-March, 1845. 51 



