settings as follows: Photomultiplier - 

 set to null dark current; sensititivity 

 control - midpoint; wave length - 372 

 m mu; selector switch - 0.1; photo- 

 tube resistor - 10,000 megohms; slit 

 width - adjust to zero meter needle on 

 200 p. p.m. ferric oxide at 100 percent 

 emission; acetylene pressure - 4.3 

 p.s.i.; oxygen pressure - 9.3 p.s.i. 

 Bracket the net emission of the un- 

 known by reading the appropriate pair 

 of standards from the prepared series 

 of standards innmediately after read- 

 ing the unknown. Report the concentra- 

 tion as percent ferric oxide on dry 

 weight basis. 



Manganous oxide 



Reagents and Apparatus: 



1. 3N hydrochloric acid (HCl) - 1 

 volume of concentrated hydro- 

 chloric acid and 3 volumes of dis- 

 tilled water. 



2. 6N hydrochloric acid (HC 1) - equal 

 volumes of concentrated hydro- 

 chloric acid and distilled water. 



3. Concentrated nitric acid (HNO3). 



4. Amber lite IRA 400 (OH) - anion 

 exchange resin (manufactured by 

 Rohm and Haas Company). 



5. Manganese dioxide (Mn02) stand- 

 ard solution (500 p. p.m.) -dissolve 

 0.2500 grn. of manganese dioxide 

 in 20 ml. of 6N hydrochloric acid; 

 heat until dissolved and dilute to 

 500 ml. with distilled water. 



6. Calciunn oxide (CaO) solution 

 (10,000 p.p.m.) - dissolve 4.4617 

 gms. of calcium carbonate (CaCO 3) 

 in 20 ml. of 6N hydrochloric acid 

 and dilute to 250 ml. with dis- 

 tilled water. 



7. Anion exchange column - the col- 

 umn is made by placing a plug of 

 glass wool above the stopcock of a 

 50 -ml. buret and adding amberlite 

 IRA 400 (OH) anion exchange resin 

 to a depth of 30 cnn. in the buret. 

 (The column is recharged after 



each third sample is passed through 

 by washing with 150 ml. of 3N 

 hydrochloric acid and rinsing with 

 150 ml. of freshly boiled and cooled 

 distilled water.) 



Procedure : Dippel and Bricker ( 1955) 

 reported a rapid flame photometric 

 method for the determination of man- 

 ganese in a variety of materials, by 

 measuring the intensity of the man- 

 ganese line at 403.3 m mu. They found 

 the intensity to vary directly and lin- 

 early with the concentration of man- 

 ganese up to 200 p.p.nn., and that 

 interference was exhibited by phos- 

 phate, sulfate and chloride ions. We 

 used an anion exchange resin to re- 

 move interfering anions and added 

 calcium to all standards to give a 

 concentration of at least 1000 p.p.m. 

 calcium oxide to offset the effect of 

 that present in the samples. 



Weigh about 1.0 gm. of dried sample 

 into a 150-ml. beaker and add 10 ml. 

 of 6N hydrochloric acid and 5 ml. of 

 concentrated nitric acid. Heat at 

 medium setting on an electric hot 

 plate until evaporation is complete, 

 bake for 10 minutes, allow to cool, 

 and add 1 ml. of 6N hydrochloric acid 

 and 15 ml. of distilled water. Heat 

 to near boiling and filter the mixture 

 using a medium -flow filter paper (we 

 used Whatman No. 4) letting the filtrate 

 flow directly into the anion exchange 

 column. Catch the effluent in a 100-ml. 

 volumetric flask and fill to the mark 

 with distilled water. Add 10 ml. of 

 calcium oxide solution to each of a set 

 of standards containing concentrations 

 of 0, 100, 200, 300 and 400 p.p.m. of 

 manganese dioxide (prepare from 

 standard solution). 



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 

 photomultiplier and oxy-acetylene 

 flame attachment. Spectrophotometer 



