NITRATE OF SODA 109 



for analysis according to the amount of chlorides 

 present. A small quantity of potassium chromate 

 solution is added, and the flask placed on a white tile. 

 Decinormal silver nitrate solution (i c.c. = 0-00585 

 gram NaCl) is now run in from a burette, and the 

 liquid well shaken to ensure thorough mixing. The 

 titration is complete when the faint reddish tinge, due 

 to the formation of silver chromate, is permanent. 



The end-point is more readily observed by using a 

 control vessel containing the various materials with the 

 silver not present in excess. The slightest formation 

 of the red tint may then be easily seen. 



Example : — 



Vol. of solution used = 200 c.c. {i.e. 4 grams 



of fertiliser). 

 Vol. of AgNOg required = 5-8 c.c. 

 .'. Weight of NaCl present 



in 100 c.c. = 5-8 X 0-00585 gram 

 = 0-0339 gram. 

 .'. Percentage of NaCl in 



the Nitrate = 0'^^ 



{d) Sulphates. — If the qualitative examination shows 

 the presence of large quantities of sulphate, 100 c.c. of 

 the solution are acidified with hydrochloric acid, mixed 

 with some ammonium chloride solution, and brought to 

 the boil. Hot barium chloride solution is run in until 

 all the sulphate is precipitated, the barium sulphate is 

 filtered off, washed thoroughly, dried, and ignited. 

 From its weight is calculated the percentage of NagSO^ 

 in the nitrate of soda. One part of BaSO^ is equivalent 

 to 0-609 part of NagSO^. 



{e) Nitrogen. — The quantity of sodium nitrate in 

 the manure is generally determined by difference from 

 100 by subtracting the percentages of moisture, sand, 



