IV] WATERS 41 



29 DETEHMINATION. 



Preli7ninary test. — Determine the amount of the permanganate required to oxi- 

 dize the nitrite to nitrate by acidifying a preliminary sample of 50 cc. with 1 cc. of 

 the sulphuric acid and adding the permanganate until a slight pink color remains 

 after standing 10 minutes. Calculate the amount of the permanganate required for 

 a sample collected as described under 25. 



To the sample add 1 cc. of the sulphuric acid and about 0.1 cc. of the perman- 

 ganate in excess of the calculated amount required to oxidize the nitrite to nitrate. 

 If more than 10 cc. of the permanganate are required add an additional 1 cc. of the 

 sulphuric acid. Rotate the bottle and allow to stand for 10 minutes, after which 

 destroy any excess of the permanganate by adding from a pipette 0.5-1 cc. of the 

 oxalate. Insert the stopper and rotate as before. The color quickly disappears, 

 and when decolorized add approximately 2 cc. of the manganous sulphate and 2 cc. 

 of the sodium hydroxid-potassium iodid and proceed as in 26. Express the results 

 in milligrams per liter and percentage saturation.' 



MINERAL WATER. 



30 SPECIFIC GRAVITY.-TENTATIVE. 

 Determine specific gravity at -^qt by means of a pycnometer. 



31 SOLIDS IN SOLUTION.— OFFICIAL. 



Determine as directed under 7. 



32 IGNITED RESIDUE.— OFFICIAL. 



Determine as directed under 9. 



33 FREE AND ALBUMINOID AMMONIA.— OFFICIAL. 

 Determine as directed under 1 1 . 



34 NITROGEN IN THE FORM OF NITRITE. -OFFICIAL. 

 Determine as directed under 13. 



35 NITROGEN IN THE FORM OF NITRATE.— OFFICIAL. 

 Determine as directed under 15 or 17. 



36 CHLORIN.-OFFICIAL. 

 Determine as directed under 19. 



37 HYDROGEN SULPHID.— TENTATIVE. 



Place 0.5-2 cc. of N/100 iodin in a 500 cc. flask and add the water until the color 

 of the iodin disappears. Add 5 cc. of the starch indicator and then N/100 iodin until 

 a blue color appears. Fill the flask to the mark with water, noting the amount 

 added. Subtract the quantity of water, iodin solution, and the starch indicator 

 added, to determine the quantity of the water titrated. An excess of iodin is re- 

 quired to produce a blue color. A correction is obtained by adding 5 cc. of the 

 starch indicator to 500 cc. of water and then adding N/100 iodin until the color 

 matches that of the sample under examination. Correct the original titration by 

 the amount of iodin used in the blank. 



