and then replace on the bath and it will usually boil quietly. Large lumps in the 

 mass will cause bumping; therefore the sample should be as .fine as possible. Fish 

 liquefy on the steam bath, boil down quietly, and without bumping. After danger 

 from frothing has ceased, apply the full heat of the steam bath. This evaporation 

 requires about one hour. Transfer to a hot plate covered with a thin sheet of asbestos 

 and dry down gradually, running at from 130 to 160 C. at first (determine temper- 

 ature by laying a thermometer on the asbestos) ; then raise the temperature and con- 

 tinue the boiling, finally using the full heat of the hot plate, which should be suffi- 

 cient to boil off sulphuric acid. This requires from one and a half to two hours. 

 Place in a cold muffle, heat gradually until all volatile matter is driven off, and then 

 burn until all of the carbon is destroyed. This requires from two to three hours. 

 Remove from the muffle as soon as burned, cool, cover the residue with water, and let 

 stand a few minutes. Using an iron spatula, scrape and wash the contents of the 

 crucible into a 600 c. c. beaker. Cover the beaker and add gradually 40 c. c. of dilute 

 sulphuric acid (1:1) and 10 c. c. to the crucible containing some water. Rotate, scrape 

 the sides of the crucible with a spatula, and wash into the beaker. When the ^action 

 is ended, add 50 c. c. of sulphuric acid (sp. gr., 1.84) and 30 c. c. of nitric acid (sp. gr., 

 1.42). Cover with a watch glass and boil briskly on a hot plate, finally with the full 

 heat of the hot plate, until the residue gives off fumes of SO 3 . Allow to fume for 10 

 minutes, remove from the hot plate and allow to cool but not to solidify. Pass the 

 stem of a funnel bent at an angle over the lip of the beaker and under the cover glass 

 and add successively small amounts of distilled water through the funnel from a 

 wash bottle until violent action has ceased. Then add rapidly about 150 to 200 c. c. 

 more water through the funnel and remove the funnel and watch glass, washing into 

 the beaker with distilled water. Stir the cake in the beaker and wash into a 1-liter 

 erlenmeyer with distilled water. 



The total volume in the erlenmeyer at this time should be about 300 to 400 c. c. 

 Cool, pass in hydrogen sulphid for a few seconds, rotate the flask and add 28 per 

 cent ammonium hydroxid slowly until the black color of the precipitated iron sul- 

 phid just persists on rotating the flask. Immediately make acid with 1 : 1 sulphuric 

 acid and add 10 c. c. excess of the dilute acid. Dilute the contents of the flask to 1 liter 

 with boiling water and continue passing in a rapid stream of hydrogen sulphid for 

 25 minutes more, cork, and let stand over night. The next morning heat on the 

 steam bath for about half an hour, rotating the flask two or three times during the 

 heating, partly cool by setting in cold water, so that the flask can be handled easily } 

 and filter onto a 12.5 cm. ashless white ribbon paper, No. 589, washing the filter with 

 a solution consisting of 50 c. c. of glacial acetic acid and 100 c. c. of a saturated solution 

 of ammonium acetate, made up to a liter with distilled water. Wash the precipitate 

 six times with this solution, filling the filter at each washing. Return the filter paper 

 and precipitate to the erlenmeyer, add 100 c. c. of 20 per cent potassium hydroxid and 

 boil over a free flame for a couple of minutes until the filter paper is broken up and 

 the solution is clear. (The flask can be manipulated over the flame easily with a 

 large wooden test-tube holder made of strips of pine wood and rubber bands.) Im- 

 mediately decant through a double white ribbon filter paper of 12.5 cm. into a 400 

 c. c. beaker, washing the flask and filter with successive portions of hot water until the 

 filtrate comes through colorless. The filtrate will have a volume of about 200 to 

 300 c. c. Add 20 c. c. of concentrated hydrochloric acid to this solution, stir, add a 

 few drops of phenolphthalein and add concentrated hydrochloric acid from a burette 

 until the dark color of the solution disappears, then add 1 c. c. excess of the acid. Test 

 with a strip of litmus and see that the solution is acid, stir well, place on a steam 

 bath, heat for 20 minutes, cover, and let stand over night. 



In the morning test the supernatant liquor, which should be perfectly clear and 

 brilliant, with a piece of blue litmus. If not acid, make so with concentrated hydro- 

 chloric acid and then add an excess of 1 c. c. If the supernatant liquor is acid and 

 [Cir. 67] 



