4. When the samples have thawed to 

 room temperature, shake thoroughly and clean 

 the cap-glass junction with a jet of dis- 

 tilled water. Remove cap, and with a large 

 bore 25-milliliter graduated pipette, dis- 

 pense 25-milliliter portions into the 

 appropriate flask, 



5. Upon completion of the dispensing 

 operation remove the total phosphate set and 

 place flasks in digester. Adjust controls 



to digest for either 3 hours at a steam pres- 

 sure of 85 + 5 pounds per square inch or 5 

 hours at a steam pressure of 30 + 5 pounds 

 per square inch, 



6. With a 2-milliliter automatic 

 pipette, add 0.75 ml. of the molybdate 

 reagent to each inorganic sample. Shake 

 immediately after the addition. 



7. Add 1 drop of stannous chloride 

 reagent to the first sample flask and then 

 swirl the flask thoroughly. Thirty seconds 

 later, add a drop to the second flask and 

 swirl. Continue at 30-second intervals 

 until all flasks have been treated. 



8. Determine the density of the blue 

 color that will develop if there is any 

 phosphate present, with a Fisher a.c. elec- 

 trophotometer equipped with a 650 A filter 

 and a 23-milliliter cell. Color-density 

 determinations are made 30 minutes after the 

 addition of the stannous chloride reagent. 

 If analyst cannot check a sample every 30 

 seconds, increase the time interval in item 

 5 as necessary. 



b. Stannous chloride reagent. 

 The same as that listed under Inorgan- 

 ic Only. 



Total Onl y 



1. If samples are frozen, thaw by 

 placing in front of an electric fan. 



2. While samples are thawing, set up 

 enough 50-milliliter pyrex Erlenmeyer flasks 

 for duplicate analysis. 



3. To each flask add 0.38 ml. of 18N 

 H2SO4,— ' and with a large bore 25-milli- 

 liter graduated pipette, a 25-milliliter 

 portion of the sample. Before removing cap, 

 clean the cap-glass junction with a jet of 

 distilled water. 



4. Place samples in the autoclave 

 and digest for a period of 3 hours at a 

 steam pressure of 85 + 5 pounds per square 

 inch. 



5. Remove samples and cool to room 

 temperature. Adjust volumes at 25 ml. by 

 adding triple-distilled water. Add 0.75 ml. 

 of molybdate reagent to each flask (see 

 reagents under Total and Inorganic) and 

 swirl . 



6. Add 1 drop of stannous chloride 

 reagent to the first sample flask and then 

 swirl the flask thoroughly. Thirty seconds 

 later, add a drop to the second flask and 

 swirl. Continue at 30-second intervals 

 until all flasks have been treated. 



9. Convert the recorded density units 

 (-log T) to concentration units (ug at PO^- 



P/1) by dividing by the slope ~ °^ 



% -P/l 



\ig at 



obtained by running known standards along 

 with the unknown samples. 



10. After the total phosphate samples 

 have been digested for the required time, 

 remove them from autoclave. Adjust all 

 volumes to 25 ml. with triple-distilled 

 water and treat exactly as indicated for the 

 inorgcinic set, starting with item 6. 



Reagents : 



a. Molybdate reagent. Dissolve 

 3.3 gm. ammonium molybdate in 200-mil- 

 liliter triple-distilled water to which 

 has been added 3 ml. of 36N H2SO4. 



7. Determine the density of the blue 

 color that will develop if there is any 

 phosphate present with a Fisher a. c. elec- 

 trophotoraeter equipped with a 650 A filter 

 and a 23-milliliter cell. Color-density 

 determinations are made 30 minutes after the 

 addition of the stannous chloride reagent. 

 If analyst cannot check a sample every 30 

 seconds, increase the time interval in item 

 5 as necessary. 



8. Convert from density to concentra- 

 tion units by comparing with standard sam- 

 ples that were run with the regular samples. 



1/ Omit if acid was added inmediately after 

 sample collection. 



