106 On the Composition of the Ancient Ruby Glass. [Feb. 



bility of the basis on which it is flashed, that which is now manu- 

 factured being of flint, while the former is of the hardest crown 

 glass; also the difficulty of obtaining it of any size, and free from 

 cloudiness or opacity : to ascertain the composition of the 

 ancient glass, I made the following experiments. 



A quantity of the glass was sent me by Mr. Charles Muss, and 

 such pieces were selected for examination as were free from 

 decomposition, and of the deepest colour: these were powdered 

 in a stone mortar, and afterwards mixed with four times 

 their weight of carbonate of potash ; the mixture was heated to 

 fusion in a hessian crucible, and the fusedmass poured out while 

 fluid. This was afterwards powdered and digested in muriatic 

 acid, which dissolved nearly the whole, what remained appear- 

 ing to be mostly silex. The acid solution was slowly evaporated 

 nearly to dryness, and distilled water poured on the mass, 

 to wash it. To the filtered solution ammonia was added 

 in excess, which threw down an abundant precipitate of 

 oxide of iron, the supernatant fluid acquiring a deep blue tinge, 

 which, upon examination, proved to contain only copper. 

 The filter that contained the silex stood for some hours near a 

 window, and the surface of the silex gradually assumed a deeper 

 colour, approximating at last to a deep brown. Suspecting it to 

 contain muriate of silver, I washed it with a solution of ammonia. 

 On adding muriatic acid to the filtered solution, a copious preci- 

 pitate of chloride of silver ensued. 



The precipitate of iron, and the ammoniacal solution containing 

 the copper, were carefully examined for other substances, and 

 particularly for manganese, which I know has been suspected to 

 enter into the composition of this coloured glass, but 1 was not 

 able to detect the smallest portion. The only substance I found, 

 except those I have mentioned, was a slight trace of lime. 

 From the above, it is evident the composition of this glass may 

 be stated to be 



Silex, 



Oxide of copper, 



Oxide of iron, 



Oxide of silver, 



Lime. 



It is difficult to decide whether the oxide of iron enters into 

 the composition of the coloured portion of the glass, or into 

 the bases or substance of it, or both. I detached some small 

 fragments of the uncoloured portion, and made a separate exa- 

 mination of them, and they proved to contain abundance of iron. 

 It is also difficult to determine what alkali has been used as 

 a flux for the siliceous matter. The quantity of lime I obtained 

 was certainly much too small to produce the effect, but I have 

 some reason to suspect the alkah to be soda. 



To endeavour to determine the exact proportions of the above 



