after each third sample is passed 

 through by washing with 150 ml. of 

 3N hydrochloric acid and rinsing 

 with 150 ml. of fres'nly boiled and 

 cooled distilled water.) 



Procedure : The method used in deter- 

 mining calcium is a modification of a 

 successful application of the flame 

 method to a complex material of fairly 

 high calcium content reported by 

 Standen and Tennant (1956), and uti- 

 lizing an anion interference removal 

 procedure described by Beckman 

 Instruments, Inc. (1955). 



Weigh 0.1-1.0 gram of sample de- 

 pending upon the apparent CaO content) 

 into a I50-ml. beaker. (Insoluble 

 residue was determined previous to 

 CaO--and CaO content varies some- 

 what inversely to that of insoluble 

 residue.) Add 10 ml. of 6Nhydrochloric 

 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 hydro- 

 chloric acid and 15 ml. of distilled 

 water. Heat to near boiling and filter 

 this mixture using a medium -flow filter 

 paper, letting the filtrate flow directly 

 into the anion exchange column. Catch 

 the effluent in a 100-ml. volumetric 

 flask, fill flask to mark with distilled 

 water and set aside for flame analysis. 



Make up a set of standards in con- 

 centrations of 0, 500, 600, 700, 800, 

 900, and 1000 p. p.m. CaO from the 

 1000 p. p.m. CaO 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 attachments. Spectrophotometer 

 settings as follows: Photomultiplier - 

 set to null dark current; sensitivity 

 control - clockwise extreme; wave 

 length - 554 m mu; selector switch - 



0.1; phototube resistor - 10,000 

 megohms; slit width - adjust to zero 

 meter needle on 1000 p. p.m. calcium 

 oxide standard at 100 percent trans- 

 mission; acetylene pressure - 3.5 

 p.s.i.; oxygen pressure - 9.1 p.s.i. 

 Bracket the net emission of the un- 

 known by reading the appropriate pair 

 of standards from the prepared series 

 of standards immediately after read- 

 ing the unknown. Report the concen- 

 tration as percent calcium oxide on dry 

 weight basis. 



Phosphorus pentoxide 



Reagents and Apparatus: 



1, 3N hydrochloric acid (HCl) - 1 

 volume of concentrated hydro- 

 chloric acid and 3 volumes of 

 distilled water. 



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

 volumes of concentrated hydro- 

 chloric acid and distilled water. 



3. Concentrated nitric acid (HNO,). 



4. Dowex 50x8 - cation exchange 

 resin. (Dow Chemical Company). 



5. Phosphorus pentoxide (P2O5) 

 standard solution (500 p. p.m.) - 

 dissolve 0.5000 gm. of anhy- 

 drous sodiunn dibasic phosphate 

 (Na2HP04) in recently boiled (CO2 

 free) distilled water and allow to 

 flow through a cation exchange 

 column. Catch effluent in a 500- 

 ml. volumetric flask and dilute to 

 500 ml. with distilled water. 



6. Calcium oxide (CaO) solution 

 (10,000 p. p.m.) - dissolve 8.9236 

 gms. of calcium carbonate (CaC03) 

 in a slight excess of 6N hydro- 

 chloric acid (about 25 ml.), evap- 

 orate to dryness, redissolve in 

 6N hydrochloric acid and dilute to 

 500 ml. with distilled water. 



7. Cation exchange column - the col- 

 umn is made by placing a plug of 

 glass wool above the stopcock of 

 a 50-ml. buret and adding 20 to 

 50 mesh Dowex 50x8 cation ex- 

 change resin to a depth of 30 cm. 



10 



