^O-t Mr. J. Andrews on the Detection 



also seen a Roman lachrymatory and an image of one of the 

 divinities of Egypt, which seem to be of the same manufacture. 

 It is probable that this blue glass was originally an Egyptian 

 invention, for Pliny ascribes the discovery of a mode of fabri- 

 cating a factitious lapis lazuli to a king of Egypt*. 



LIV. On the Detection of Baryta or Strontia when in imioti 

 with Lime. By Mr. J. Andrews f. 



THE best method which has yet been proposed to distin- 

 guish strontia when combined with lime, is perhaps that 

 by which Slromeyer fii'st succeeded in determining the com- 

 position of arragonite ; and I believe, it alone has been em- 

 ployed in the analyses that have been made by different che- 

 mists of tl)e varieties of that mineral. It is founded upon the 

 insolubility of nitrate of strontia in pure alcohol, which at the 

 same time dissolves with facility the nitrate of lime. In theory 

 the process is absolutely perfect; and when properly con- 

 ducted, it seems susceptible in practice of very great precision ; 

 but it must at the same time be confessed that its failure in 

 the hands of some of the most expert chemists proves it to 

 be a far from satisfactory mode of analysis. As nitrate of 

 baryta is insoluble in alcohol, baryta may likewise in this man- 

 ner be separated from lime. 



Bucholz having endeavoured unsuccessfully to verify the ana- 

 lysis of Stromeyer, suggested another process, which, though 

 he failed himself in executing, was afterwards performed by 

 Gehlen. It consisted in separating the strontia from the greater 

 part of the lime (the mixture being previously reduced to the 

 pure state) by solution in boiling water, and afterwards distin- 

 guishing the presence of the former by the crystallization of 

 its hydrate on allowing the solution to cool. It is evident that 

 although in this way considerable quantities of strontia may 

 be detected, yet when it exists in small proportion, the process 

 will entirely fail, in consequence of the solubility of strontia in 

 cold water. If baryta be substituted for strontia, this method 

 will be still more defective, since that earth is much more so- 

 luble in water than strontia. 



Mr. Brande has proposed to precipitate directly the sul- 



* In the 23r<l volume of the Annals of Philosophy, p. 116, are some re- 

 marks by Mr. Sniithson, on the colours found on the tomb of the Egyptian 

 King Psammis : " The blue is what most deserves attention ; it is a smalt or 

 glass powder, but its tingeing matter is not cobalt, but copper. Many years 

 ago I examined the blue glass with which was painted a small figure of Isis 

 brougiit to mc from Egypt, and found its colouring matter to be copper. 

 I am informed that a fine blue glass cannot at present be obtained by means 

 of copper :— what its advantages would be above that from cobalt it is for 

 artists to decide.' t Communicated by the Author. 



phate 



