34 TESTING MISCELLANEOUS SUPPLIES. 



determination of iron reduce with zinc, titrate with standard potassium per- 

 manganate, and calculate to ferric oxid. For the determination of manganese 

 transfer 100 cc of the solution (corresponding to 1 gram) to a 500 cc flask, 

 add sodium hydroxid solution until nearly but not quite neutral. Then add 

 an emulsion of zinc oxid in water in slight excess, shake until all of the iron 

 is thrown down, fill to the mark, mix, let settle, filter through a dry paper, and 

 use portions of 100 cc (corresponding to 0.2 gram) for the manganese deter- 

 mination. Transfer to a 300 cc Erlenmeyer flask, heat to boiling, titrate with 

 standard permanganate. The flask must be shaken during the titration and 

 some experience is necessary to determine the end point, which is best seen by 

 looking through the upper layer of liquid and observing when the pink tinge 

 from the permanganate does not disappear on shaking. A standard potassium 

 permanganate solution, the iron factor of which is known, may be used to de- 

 termine manganese. The iron factor multiplied by 0.2952 gives the manganese 

 factor. In some cases this method of attack will not separate all of the iron 

 from the insoluble matter. In such a case the insoluble must be fused with a 

 mixture of sodium and potassium carbonates, dissolved in water, evaporated 

 with excess of sulphuric acid, filtered from the insoluble, and this solution added 

 to the first one. 



Another method is as follows: Roast 5 grams of the powder, digest with 

 25 cc 'of hydrochloric acid, evaporate to dryness, moisten with hydrochloric acid, 

 dissolve in water, filter, and wash the residue ; ignite the residue in a platinum 

 crucible, add sulphuric acid and hydrofluoric acid, drive off the latter, and heat 

 until copious fumes of sulphuric anhydrid come off. Add potassium hydrogen 

 sulphate and fuse, dissolve in water, filter from any remaining insoluble (barium 

 wilphate), unite the two solutions, make up to 500 cc, and use aliquots for the 

 iron and manganese determinations. For the determination of iron place 

 100 cc in a flask, add about 3 grams of zinc, put a funnel into the neck 

 of the flask, heat when the action slackens; if basic salts separate out add a 

 few drops of hydrochloric acid. When all of the iron is reduced, add 30 cc of 

 sulphuric acid (1:2), and as soon as all of the zinc is dissolved and the solution 

 is cool, titrate with potassium permanganate. 



For the determination of manganese use 50 cc, evaporate to a very small 

 bulk, add strong nitric acid and evaporate the hydrochloric acid; add 75 cc 

 of strong nitric acid, which should be free from nitrous acid, and 5 grams of 

 potassium chlorate, heat to boiling and boil fifteen minutes; then add 50 cc of 

 nitric acid and more potassium chlorate. Boil until yellow fumes cease to 

 come off, cool in ice water, filter on asbestos and wash with colorless, strong 

 nitric acid; su k dry and wash out the remaining nitric acid with water, 

 transfer the precipitate and the asbestos to a beaker, add a measured excess 

 of standard solution of ferrous sulphate in dilute sulphuric acid, stir until all 

 of the manganese dloxid Is dissolved, and titrate the remaining ferrous sulphate 

 with potassium permanganate. A ferrous solution of about the proper strength 

 Is made by dissolving 10 grams of crystallized ferrous sulphate in 900 cc of 

 water and 100 cc of sulphuric acid (specific gravity 1.84). This solution is 

 titrated with standard potassium permanganate. The reaction taking place 

 tin- manganese dloxid, acts on the ferrous sulphate is MnO 2 +2FeSO 4 -h 

 jii so=MnSO+Fea(SO 4 )+H 2 O. Hence the iron value of permanganate 

 multiplied by 0.491 gives the value in manganese. 



3. Blue Pigments. 



There are two important blue pigments used in painting, Prussian blue and 

 nltramarine. Of minor Importance and very little used in paints for anything 

 but artists' colors are cobalt blue and smalt. 



