38 TESTING MISCELLANEOUS SUPPLIES. 



in all), to oxidize the Prussian blue; add about 25 cc more of water and boil 

 for some time, so as to decompose all of the hydrogen peroxid. Acidify with 

 hydrochloric acid, boil, filter, and wash. Transfer the residue again to the 

 casserole and boil with a solution of ammonium chlorid (slightly alkaline) to 

 dissolve the last trace of lead ; filter, wash, ignite, weigh the insoluble impuri- 

 ties, and determine their nature. They are probably barytes or silica. 



Heat another 1 gram portion very gently in a casserole or small porcelain 

 dish, and remove from the flame as soon as it begins to glow. The heating 

 should be carried out very carefully, the object being to decompose the Prussian 

 blue but not to heat it enough to render the iron difficultly soluble. Allow to 

 cool, add hydrochloric acid, and digest covered on the steam bath for an hour. 

 As a general rule this treatment brings everything except insoluble impurities 

 into solution. Cool, dilute to 300 cc, and pass in a rapid stream of hydrogen 

 sulphid until all of the lead is precipitated; filter, wash with water containing 

 some hydrogen sulphid, boil off the hydrogen sulphid from the filtrate, add 

 bromin water to oxidize the iron, add ammonium hydroxid in slight excess, 

 filter, dissolve the precipitate in hydrochloric acid, reprecipitate with ammonium 

 hydroxid, filter, wash, unite the filtrates, and determine calcium and magnesium 

 in the usual way. 



(3) QUANTITATIVE DETERMINATION OF YELLOW AND BLUE. 



The examination for impurities is usually sufficient, but if a quantitative 

 determination of yellow and blue be desired, the sulphate may be determined 

 in the united filtrate from the insoluble impurities by precipitating from hydro- 

 chloric acid with barium chlorid. The ferric ferricyanid present will not cause 

 any difficulty if the barium sulphate is filtered off soon after precipitating; 

 but if it is allowed to stand a long time a reduction is likely to take place with 

 the re-formation of some Prussian blue. 



Determine the lead in the second portion by dissolving the lead sulphid in 

 nitric acid, boiling the residues with ammonium acetate, uniting the filtrates, 

 adding sulphuric acid, heating to fumes, and completing the determination of 

 !; id as sulphate in the usual manner. For iron and chromium dissolve the 

 ammonia precipitate in hydrochloric acid, make up to definite volume, deter- 

 mine the iron in an aliquot by reduction and titration with potassium perman- 

 ganate or potassium dichromate. Determine the chromium in another aliquot 

 a< described under chrome yellow. 



(4) MISCELLANEOUS DETERMINATIONS. 



If aluminum is present, precipitate another aliquot with ammonium hydroxid, 



wash. dry. i-nite. and weigh. From the iron and chromium determinations 



calculate the combined weight. of ferric oxid and chromium oxid and obtain 



aluminum \'n! by difference. Determine the moisture and the nitrogen as 



i ibed under Prussian blue. 



If (he presence of ultramarine is suspected, test with hydrochloric acid, and 

 if hydrogen sulphid is evolved, ultramarine is present. 



(b) ULTBAMARINK AND ZINC YELLOW GREEN. 



(1) GENERAL DISCUS'SION. 



No lead compounds should be in this green, since with lead and ultramarine 

 the | .Mint will soon be blackened by the formation of lead sulphid. Owing to 

 the widely varying composition of ultramarine, it is not possible to make a 



