£68 



FORMATION OK BASALTES;. 



On Artificial Sandstones, that have undergone a regular Con- 

 traction in the Fire; by Mr. Alluau*. 



Composition 

 pi the stone. 



Artificial sand \_>N examining with Mr. Leopold Cbevaillers the scoria 

 ^one separate p rcK j ucec j u , the operation of parting bell metal, winch was 

 performed under his direction at Limoges, I found masses 

 of artificial sandstone, which by a regular contraction had 

 divided itself into prisms, precisely resembling the basaltic 

 columns, that exist in all volcanic countries. 



These sandstones, which served as a cupel to the melting 

 furnace, are composed of a fine-grained sand, the remains 

 of granites; the other component parts of which had been 

 decomposed. To separate them, and obtain the purest si~ 

 liceous grains, they were carefully washed and decanted, 

 f hey were afterward mixed with water loaded with clay, to 

 impart to them the body requisite for their use; and a little, 

 charcoal powder was added, which, diminishing the points 

 of contact between the siliceous particles and the metallic 

 oxides, rendered them less vitrescible, and thus prolonged 

 the duration of the cupel of the furnace. 



To form it, a stratum of this mixture 15 to 20 cent. [6 or 

 8 inches] thick was placed on the floor of the furnace, and 

 strongly beaten down as it was gradually dried by a gentle 

 heat. After being used a certain time, it was necessary to 

 renew the whole stratum, and all the sandstones arising from 

 it had experienced the same contraction. 



The upper part of these prismatic sandstones is covered 

 with a scorified metallic stratum 4 or 5 cent, [about ]§ or 2 

 inches] thick, that serves to hold together all the prisms, 

 which are notwithstanding easily separable. The degree of 

 heat has been more intense near this stratum, than in the 

 inferior part : accordingly the sandstone there is harder and 

 more compact, being difficult to penetrate; while the 

 other extremity of the prism is easily crumbled by the fin- 

 gers. 'The fire however has been sufficiently violent through- 



Mannef in 

 which it was 

 ttwaied. 



Its texture. 



* Abridged from the Journal de Physique, vol. LXV, p. 229. 



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