IRON 



279 



Standard Ferric Ammonium Sidfate. Prepare a soln. in 3 A?" sulfuric 

 acid such that 5 ml. requires a vol. of titanous sulfate equivalent 

 to 100-200 mm. on the burette. 



Sodium Chloride (Powdered). 



50% Formic Acid in Ether. Redistill each component from glass, 

 and mix just before using. 



Fig. 93. Modified Conway burette. A, pressure-regulating vessel; B, C, D, 

 G, and H, stopcocks; E, the burette, standard-bore capillary tubing against 

 mm. scale (10 cm. o 0.05 ml.); F, Ti2(S04)3 reservoir, capacity 200-250 ml.; 

 /, digestion and titration flask. From Ramsey (1944) 



PROCEDURE 



1. Add the sample (0.2 ml. blood) to 0.2 ml. each of the nitric 

 and perchloric acids and 0.5 ml. sulfuric acid in a digestion flask. 

 Add a boiling chip and heat with shaking over a micro flame. The 

 mixture darkens, then clears, and just before the last of the perchloric 

 acid boils off the mixture becomes a clear deep greenish-yellow for 

 3-5 sec. Continue heating for 3 sec. after the disappearance of this 

 color. 



2. If copper is present, dilute the cooled digest with 2 ml. water 

 and transfer as completely as possible to a narrow test tube. Rinse 

 the flask with two portions of 1 ml. water and add the rinsings to the 

 test tube. Add 0.5 ml. sulfuric acid and saturate the soln. with sodium 

 chloride. Shake the tube twice with 2 ml., and twice with 1 ml. 5% 



