ON THE EFFECTS OF LONG-CONTINUED HEAT. 187 



crucible, with no adhesion to its sides, a perfect cast ; no salt had been added 

 to it, nor is any separable from it by boiling. The close cohesion of the 

 grains of sand by the action of heat may have been facilitated by the inter- 

 mixture of some impurities, referable to oxide of iron, and possibly to felspar. 

 The only vestige of the plant is a skin of silica on the surface of the place 

 which it occupied in the interior of the sand, coating the vacancy, but not 

 furnishing an impression from which the character of the plant can be re- 

 covered. The stone showed signs of splitting from shrinkage in an oblique, 

 or nearly vertical direction, a tendency which might probably have been more 

 conspicuous had the experiment been on a larger scale. 



The other specimen is a translucent mineral of a pure blue colour. This 

 colour it does not lose when heated red-hot in the outer flame of a candle. 

 Melted into a bead with carbonate of soda, it passes into a pure opake white ; 

 the same also with a small proportion of borax ; when the proportion of the 

 borax is increased, the bead is transparent and colourless ; dissolved in 

 hydrochloric acid, the mineral loses its colour. The solution contains much 

 sulphate of lime, and some silica and alumina, whether potash also, or soda, I 

 have not determined ; tested with prussiale of potash, it shows no trace of 

 copper, and none, or scarcely any, of iron. This substance therefore belongs 

 to the class of minerals of which Lapis lazuli and Haiiyne are varieties. It has 

 been formed irregularly under a thin crust of sand to which it adheres, is im- 

 bedded in sulphate, sulphide, and carbonate of lime, and accompanied with 

 crystallized fluoride of lime. Whether this fluoride is a recomposition, or 

 part only of the original mixture from which the blue mineral has been 

 derived, I cannot say. The crucible certainly contained pounded fluor, and 

 a sulphate, which underwent decomposition, and partially decomposed the 

 fluoric crystals. 



But the objects to which I have alluded as possessing a new and unexpected 

 interest, are the metals above mentioned as having been supplementarily 

 placed, outside the boxes, under the bottom stone of the Low Moor furnace. 

 The specimens consisted, originally, of pieces, of which chromographic plates 

 have been appended to this Report, cut from a bar of zinc, a block of tin, 

 a pig of lead, and a plate of tile-copper. They occupied, severally, the places 

 marked in the accompanying ground plan of the furnace, 1, 2, 3, 4, as 

 numbered at the time of the deposit. It will be seen that none of these 

 pieces have undergone fusion, that of which the melting-point is lowest (the 

 block tin) preserving perfectly its dimensions, the exact shape into which it 

 was cut, and the sharp edges of the cutting. The external coat of the 

 tin, to the depth of from ith to ^th of an inch, is converted into deutoxide, 

 crystalline, transparent, and of the same specific gravity as the native ore ; 

 between this and the metal, intervenes in some parts a space, which, with 

 the striation of the metallic surface, indicates that a portion of the substance 

 has been dissipated. 



Of the bar-zinc, more than half has been changed, though it preserves its 

 original form, into a mass of crystalline oxide, interspersed with globules of 

 the metal, burrowed in all directions with drusy cells and cavities, and 

 showing extensive sublimation into the indurated sand which envelopes it. 

 The nature of the sublimation is manifested by a number of prismatic spicula 

 of metallic zinc, about £th of an inch long, standing within the cavities. 



But that which is chiefly remarkable is the tile-copper, in respect both to 

 the temperature at which it has been volatilized, and the combination and 

 interpenetration which its molecules, in a volatile state, have effected with its 

 nearest neighbour, the lead. I have caused a drawing to be made of these 

 specimens in their relative positions, as they lay in proximity to, but not 

 touching, each other, having a portion of sand interposed. 



