ttkh a Coating of Chalcedony. 345 



put a little of the former, with silex, in the same preparation 

 of potash and alumine. 



These two experiments were made in crucibles of platina, 

 and the success exceeded my hopes, although they had not 

 been preceded by any preliminary trial in order to regulate the 

 doses of the agents or the duration and intensity of the fire. 

 The silex was not altered in the interior ; it only assumed at 

 its surface a very slender white covering,of an uniform thick- 

 ness, forming one body with the mass, not aUackable by 

 the acids, and of such a hardness that it soon wore out the 

 stones made use of by the engravers ; and it was no more 

 affected bv the application of adamantine spar, or corindon, 

 to it, than was the covering of the sculptured head. 



These pieces came out of the crucible dull white, as I ex- 

 pected ; but some parts, which I wrought in the manner of 

 hard stones, showed that they were susceptible of the same 

 polish as that of the sculptured head. 



It cannot be denied that such a perfect imitation is fa- 

 vourable to the opinion that the covering of the head was 

 the work of art. We are not, however, entitled to suppose 

 that the chemical affinities which led to this imitation were 

 known to the artist who executed this monument; it is not 

 the first process discovered by accident long before the dis- 

 covery of the true theory. 



This opinion, however, has not obtained general assent. 

 Those, who oppose it chiefly support themselves upon the 

 resemblance of the coverings of several silices found in the 

 environs of Femes, specimens of which have been presented 

 to the class by M. Chaptal, and which in fact present upon 

 borne of their surfaces panicles of enamel, if not equal in. 

 colour and thickness, at least as shining. 



Others are of opinion, with M. Fourcroy, that whether 

 the covering of the sculptured head had been formed in the 

 earth in the same manner as the crust of these silices, or 

 whether they had been added alter the labour of the sculptor 

 by a process of art; yet, in all cases it must be acknowledged 

 that it had received the polish from the hand of man, and 

 this is the only method of reconciling the results which we 

 arc forced to draw from its actual state. 



In 



