The Phosphates of America. 



171 



duced to the ferrous state and the permanganate solution is then 

 added until all the iron is peroxidizecl, a fact which is demon- 

 strated directly the color of the iron solution turns purple. The 

 quantity of permanganate used in the operation is the measure of 

 the iron present, as may be gathered from the equation : 



10FeS0 4 +8H 3 SO 4 +2KMn0 4 ^5Fe 2 (S0 4 ) 3 +K 2 SO 4 +2MnSO 4 +8H 2 O. 



The solution may be conveniently made of quinquenormal 

 strength. Dissolve 3.162 grammes of very dry permanganate of 

 potassium in one litre of water and keep in a stoppered bottle. 

 Every c.c. of the solution should be equal to .0056 Fe'or .0080 

 Fe s 3 . 



To ascertain its exact strength, which is a very important point 

 considering the small amounts of iron we are generally called 

 upon to determine, dissolve one gramme of double sulphate of iron 

 and ammonium in 20 c.c. of water and 5 c.c. dilute sulphuric acid. 

 If 25 c.c. of the permanganate are required to produce a faint 

 pink color, permanent for two minutes, the solution is sufficiently 

 correct. One hundred c.c. of this solution may be diluted to one 

 litre with distilled water and labelled -gL- N. permanganate solution, 

 every c.c. of which = .00080 ferric oxide. 



SYMBOLS, MOLECULAR WEIGHTS, AND PERCENTAGE COMPOSITION, OF SUB- 

 STANCES USED IN THE FERTILIZER INDUSTRY. 



