36 TESTING MISCELLANEOUS SUPPLIES. 



(5) OTHER DETERMINATIONS. 



It is seldom worth while to make any further determinations. If desired, 

 however, the iron and aluminum may be precipitated as hydrates by ammonium 

 hydroxid and weighed together as oxids, and the aluminum obtained by differ- 

 ence after determining the iron volumetrically and calculating to ferric oxid. 

 The filtrate from the iron oxid and alumina precipitate may be made up to a 

 definite volume and one aliquot taken for the determination of sulphate and 

 another evaporated with sulphuric acid, ignited, and weighed. Determine 

 whether the alkali is sodium or potassium and subtract the alkali metal corre- 

 sponding to the sulphate (SO 4 ) found. The remainder is double alkali iron 

 ferrocyanid. Well-washed blues should be neutral in reaction. The red shade 

 may be due to organic red. Test the solubility in alcohol, etc. 



(b) ULTRAMARINE. 



Ultramarine is a compound of unknown constitution made by heating clay, 

 soda, sulphur, and charcoal together. It appears to be complex silicate and sul- 

 phid of aluminum and sodium. Ultramarine may be readily distinguished 

 from Prussian blue by being dissolved in hydrochloric acid with the evolu- 

 tion of hydrogen sulphid. It can not be mixed with lead pigments on account 

 of the sulphid present. Good ultramarine gives little tarnish on polished cop- 

 per. An analysis is of little value, but if desired may be conducted as follows : 



(1) MOISTURE. 

 Dry 2 grams for two hours at 105 C. 



(2) SILICA. 



Treat 1 gram with 20 cc of hydrochloric acid (1 : 1) in a covered dish, heat 

 until decomposed, remove the cover and evaporate to dryness on a water bath, 

 moisten with hydrochloric acid and again heat to dryness, add 1 cc of hydro- 

 chloric acid, let stand five minutes, add hot water, filter, and wash the insoluble. 

 If great accuracy is desired, evaporate the filtrate to dryness, take up with 

 hydrochloric acid and water, filter, and add the precipitate to the main insolu- 

 ble. Ignite the insoluble, weigh as silicon dioxid, and test the purity with 

 hydrofluoric acid. 



(3) ALUMINUM. 



Determine the aluminum in the filtrate from the silicon dioxid by precipitat- 

 ing with ammonium hydroxid, igniting, and weighing as aluminum oxid. 



(4) SODA. 



Add sulphuric acid to the filtrate from aluminum hydroxid, evaporate to 

 drynees, Ignite, and weigh as sodium sulphate (Na 2 SCM. Calculate to sodium 

 monoxid (NaaO). If calcium is present it should be precipitated with am- 

 monium oxalate In the filtrate from aluminum hydroxid, ignited, and weighed 

 as calcium oxid and the soda determined in the filtrate from the calcium oxalate, 

 as described previously. 



(5) SULPHUR. 



Mix 1 prnm of ultramarine with 4 grams of sodium carbonate and 4 grams 

 of sodium perozid in a nickel crucible, cover with about a gram of sodium car- 



