80 Professor Hausniann on Metallurgical Phenomena 



face of a vesicular mass, it passes into a porous mass, which has 

 sometimes a striking resemblance to pumice that is formed on 

 the surface of obsidian lava, when it comes in contact with 

 water, as for instance, with the water of the sea. As the vesi- 

 cular cavities of slags and lava, guided by the motion of a more 

 or less coagulated mass, are at the same time sometimes flattened 

 by pressure, and from the position of the longer axis of their 

 figure approximate the elliptic form, even in a state of sohdity, 

 continue to point out the direction of the torrent; in like man- 

 ner, from the elongation of single particles of the glassy slags, 

 as well as of pumice, arises the thread-like structure, which must 

 not be confounded with the fibrous modification of crystal- 

 line separation. Another phenomenon appertaining to this class, 

 of similar origin to the spun glass, is found in glassy slags, viz. 

 a loose complication of the most delicate glass threads. It is 

 sometimes found in the frames of blast-furnaces when the wind 

 strikes it, and from the opposite current of air which is pro- 

 duced in this way, many small globular slags are thrust into this 

 shape and elongated. A similar phenomenon is sometimes pro- 

 duced in volcanic eruptions ; on the island of Bourbon, for in- 

 stance, in the year 1821, there was observed a shower of ashes 

 consisting of the finest glass threads. 



We may now assume, as was formerly observed, that the 

 igneous process of the earth has exerted a varying influence 

 upon mountains also of a different origin. In this respect, too, 

 a more intimate study of the productions of the foundry may 

 prove instructive. Apart from the influence which the de- 

 velopment of vapours, and the ascent of fused masses, must have 

 on the position of those masses which form the vault of the 

 grand subterraneous furnace, partly the heat, and partly the 

 heterogeneous substances might have produced changes in 

 them. The metallurgic processes give rise to phenomena which 

 bear a striking resemblance to these substances. 



To the most remarkable changes which the heat of the melt- 

 ing furnace produces in bodies which are affected by it, belongs 

 unquestionably the softening of the hard grey limestone allud- 

 ed to on other occasions (Gott. Gel. Anz. von 1816, p. 494), 

 which is used as a building stone for blast-furnaces of some 

 mining districts in Sweden, without losing its carbonic acid, or 



