A. L Day and J. K. Clement —Gas Thermometer. 457 



tion was placed in a large casserole of Berlin porcelain, dis- 

 solved in nitric and sulphuric acids and the solution then evapo- 

 rated to drive off the excess of nitric acid. This troublesome 

 operation can be greatly facilitated by the use of a crown 

 burner, though as dilution and evaporation have to be several 

 times repeated, small losses are difficult to prevent. Duplicate 

 determinations, however, proved that they were entirely neg- 

 ligible as regards the small percentage of impurities. The sul- 

 phate of copper was now dissolved in water and diluted. A 

 little HC1 was added, and after standing, the solution was fil- 

 tered. The residue left on the filter was extracted with am- 

 monia to remove silver chloride and the remaining part of it 

 was treated with aqua regia. There was still left a little silica, 

 from the porcelain dish in which the copper was dissolved. 

 The solution obtained by aqua regia after the nitric acid was 

 entirely driven out by hydrochloric acid, was tested for gold 

 by sulphur dioxide. There was no precipitate in the cold 

 even after long standing, though evaporation caused the pre- 

 cipitation of about half a milligram of black metal. This 

 remained black on heating, dissolved only partially and with 

 difficulty in aqua regia, and with sulphuric acid and ammo- 

 nium nitrate gave a faint blue color. These tests indicate irid- 

 ium, though there was too little to identify with certainty. 

 The rest of the solution which had been tested for gold was 

 precipitated by hydrogen sulphide and the precipitate was fil- 

 tered, washed and burned in a porcelain capsule. It formed a 

 yellow chloride with aqua regia, gave a precipitate with am- 

 monium chloride and a very strong test for platinum with 

 potassium iodide. This platinum did not come from the acids 

 used to dissolve the copper, since the same quantities were very 

 carefully tested by hydrogen sulphide after nearly the whole 

 portion had been driven off by heating in porcelain, and found 

 to contain not a trace. 



The solution containing the copper was then warmed and 

 saturated with sulphur dioxide. After standing, a further 

 portion of silver was precipitated, filtered off and washed. It 

 was then dissolved in a little nitric acid, precipitated again as 

 chloride and added to the main portion of the silver chloride, 

 which was dried at 130° and weighed. 



The solution still containing the copper was diluted to about 

 8 liters, and from it all but a small portion of the copper was 

 precipitated by a standard solution of potassium thiocya- 

 nate, l cc of which was equivalent to about 50 mg of copper. 

 The thiocyanate was proved to be free from heavy metals 

 by a test with hydrogen sulphide. The small amount of iron 

 which it contained was separated before the solution was stand- 

 ardized, by the addition of a little ammonium alum followed 



