Washington — Copper Crystals in Aventurine Glass. 411 



were identified beyond a doubt. "With half the above quanti- 

 ties the results were not so satisfactory. The color tests for 

 both iron and chromium are sufficiently delicate to detect even 

 smaller amounts. The sulphocyanide test will, under favor- 

 able conditions [a solution containing not over -fa per cent of 

 hydrochloric acid and an excess of sulphocyanide (5 C - CS - 1 : 15)], 

 show the presence of 0*01 m.grm. of iron in 100 0-C3, of water 

 (depth of liquid in cylinder ll om ). The yellow color of sodium 

 chromate is unmistakable in 100 c-cs- of solution containing the 

 equivalent of 0*2 m.grm. of the element. 



Summary. — The following is an outline of the method of 

 treatment. Given a mixture of the hydroxide or basic acetate 

 precipitates equivalent to 0*1 grm. of each of the three ele- 

 ments. Digest this precipitate in 100 c-cs - * of water, to which 

 10 c-cs - of hydrogen peroxide and 1 grm. of sodium (or potas- 

 sium) hydroxide have been added, until effervescence ceases.f 

 Separate the iron by filtration. Acidify the filtrate slightly 

 with acetic acid and precipitate the alumina by means of 

 ammonia. (Where small quantities are present long continued 

 boiling and a concentration of the solution may be necessary.) 

 Filter off the alumina and test the filtrate for chromium. The 

 yellow color of either the iron or alumina filtrates is charac- 

 teristic. A confirmatory and more delicate test may be made 

 by acidifying the filtrate from alumina slightly and adding a 

 few c.cs. of hydrogen peroxide, obtaining the blue color so 

 characteristic of chromium compounds thus treated. 



Chemical Laboratory, Trinity College, 

 Hartford, Aug., 1894. 



Art. LTX. — On Copper Crystals in Aventurine Glass / by 

 Henry S. Washington. 



One of the most curious products of the world-renowned 

 glass-works at Murano near Venice is the so-called "aventurine 

 glass " (vetro avvenlurino\ which owes its name, according to 

 the story, to its discovery by chance {aW avventura), some 

 brass filings having been dropped accidentally into a pot of 

 molten glass. This however was not the process by which it 

 was subsequently made, though the secret of its manufacture 

 was lost in the decline of the glass industry towards the end of 



* The volume will not materially influence the results. Unnecessary dilution is 

 however to be avoided. 



\ If the peroxide be not decomposed there is danger, on acidifying the filtrate 

 containing chromium and alumina, of a reduction of the chromate and consequent 

 precipitation. 



