concentrated and IN annnnonium hy- 

 droxide. Digest the solution 15 minutes 

 in a water bath at 65° C, let cool and 

 transfer to a separatory funnel. Extract 

 the aluminum oxinate with two 10 -ml. 

 portions of chloroform, shaking first 

 portion 2 minutes and the second por- 

 tion 1 minute. Filter extracts through 

 a chloroform -wetted filter paper, 

 catching the extracts in a 50-ml. vol- 

 umetric flask. Wash filter well with 

 chloroform, adding washings to flask 

 and filling to mark with chloroform. 



Determine the absorbancy for each 

 sample and standard with a Beckman 

 Model DU spectrophotometer with the 

 tungsten lamp light source and settings 

 as follows: Photomultiplier - set to 

 null dark current; sensitivity control - 

 midpoint; wave length - 390 m mu; 

 selector switch - 0.1; phototube re- 

 sistor - 2000 megohms; slit width - 

 0.15 mm. Plot the absorption values of 

 the standards against their concentra- 

 tions and determine the slope of the 

 resulting line. Run a set of standards 

 at least once a day. Use the reciprocal 

 of the slope of the standard curve and 

 the absorption values of the samples 

 to find the amount of aluminum oxide 

 present and report as percent alumi- 

 num oxide on dry weight basis. 



Ferric oxide 



Reagents: 



1. 6N hydrochloric acid (HC 1) - equal 

 volumes of concentrated hydro- 

 chloric acid and distilled water. 



2. Concentrated nitric acid (HNO3). 



3. Ammonium chloride (NH4CI) 20 

 percent solution - dissolve 200 

 gms. of ammonium chloride in 

 distilled water and dilute to 1 

 liter. 



4. Ammoniurh chloride (NH4CI) 1 

 percent solution - dissolve 10 

 gms. of ammonium chloride in 

 distilled water and dilute to 1 liter. 



5. Concentrated ammonium hydrox- 

 ide (NH4OH). 



6. Ferric oxide (Fe203) s t a n d a r d 

 solution (1000 p. p.m.) - dissolve 

 1.0000 gm. of oven dried (110° C.) 

 ferric oxide in 30 ml. of 6N 



hydrochloric acid and dilute to 1 

 liter with distilled water. Store 

 standard solution in a polyethylene 

 bottle. 



7. Methyl orange solution - dissolve 

 1 gm. of methyl orange in dis- 

 tilled water and dilute to 1 liter. 



Procedure : A method reported by 

 Dean and Burger (1955) for the flame 

 spectrophotometric determination of 

 iron was used in developing this method 

 for iron in marine sedinnents. 



Weigh 1.5 gms. of dry sample into a 

 150-ml. beaker and add 10 ml. of 6N 

 hydrochloric acid and 5 ml. of con- 

 centrated nitric acid. Heat at medium 

 setting on an electric hot plate until 

 evaporation is complete, bake 10 min- 

 utes, allow to cool, and add 10 ml. of 

 6N hydrochloric acid. Heat to near 

 boiling and filter through a medium - 

 texture filter paper while still hot. Add 

 three drops of methyl orange solution 

 and 15 ml. of 20 percent ammonium 

 chloride solution to the filtrate and 

 washings. Add concentrated ammonium 

 hydroxide dropwise until the methyl 

 orange end-point is reached and then 

 add 2 ml. in excess. Heat solution to 

 boiling and immediately filter through 

 open texture filter paper. Wash gelati- 

 nous precipitate with hot 1 percent 

 ammonium chloride solution discard- 

 ing filtrate and washings . Wash precipi- 

 tate through the filter paper by adding 

 10 ml. of 6N hydrochloric acid drop- 

 wise, catch the resultant filtrate and 

 washings in a 100-ml. volumetric flask 

 and fill flask to the nnark with distilled 

 water. Set aside for flame analysis. 

 From the 1000 p. p.m. ferric oxide 

 standard solution prepare a series of 

 standards with concentrations of 0, 50, 

 100, 150 and 200 p. p.m. ferric oxide. 



Measure emission intensities for 

 each sample as follows: unknown, dis- 

 tilled water, standard judged to be 

 below unknown, distilled water, stand- 

 ard judged to be above unknown, and 

 distilled water (the value obtained for 

 distilled water is subtracted from the 

 value obtained for each unknown and 

 each standard) using a Beckman Model 

 DU spectrophotometer equipped with 

 photomultiplie r and oxy -acetylene 

 flame attachment. Spectrophotometer 



