198 METHODS FOR THE ANALYSIS OF BLOOD 



acid to 2 c.c. of the standard iron solution containing 0.009 mg. 

 of Fe per c.c., and keeping it in the water bath for two to four 

 minutes. It also is made up to 5 c.c. with water, to 10 c.c. with 

 5 N NHLjCNS, and to 20 c.c. with acetone in a narrow graduate, 

 which is stoppered and shaken. After the shrinkage incidental to 

 the mixture of fluids, acetone is added up to 20 c.c. and the graduate 

 is stoppered and shaken. 



Allow both graduates to stand for five minutes. 



Comparison may be best made in a Duboscq or Kober colorim- 

 eter, with the standard set at 10. The calculation is X45 = 



K 



number of mg. of Fe per 100 c.c. of blood. The comparison must 

 be made as quickly as possible, as the acetone evaporates on expo- 

 sure to the air, although about equally in both cups. 



Obtaining Blood. The ubiquity of iron makes special care to 

 avoid outside contamination necessary in obtaining the blood. 

 The finger or ear lobe should be well cleansed with water and ether 

 before pricking. A free flow, without squeezing, should be obtained. 

 Citrate and oxalate do not interfere with the determination, so 

 that blood drawn by venepuncture and so treated can be analyzed 

 for iron by the method. Corpuscles and plasma should, of course, 

 be well mixed before being drawn into the pipette. If possible, the 

 blood should be drawn in the morning before breakfast in order 

 to have as constant a condition of the blood volume as possible. 



The pipette should be calibrated by weighing the water it 

 holds. The blood should always be rinsed into the 2 c.c. of water 

 plus 0.2 c.c. of 0.1 N HC1. The least amount of blood with which 

 the determination may be made satisfactorily is 0.040 c.c. 



Hydrobromic Add. The hydrpbromic acid is the pure con- 

 centrated hydrobromic acid, 34 per cent strength. The drops 

 delivered from the pipette are of approximately 0.1 c.c. each. 

 If the two drops added to the permanganate coagulum do not 

 clear it up on boiling, another drop may be added to it as well as 

 to the standard. 



Permanganate. The permanganate used should be iron-free, 

 as determined by a blank. If it is not, repeated recrystallization 

 of the commercial product is necessary. Reliable commercial 

 firms, however, furnish an iron-free permanganate. The 0.1 N 

 solution should be kept from the light in a dark bottle. 



Standard Iron Solutions. These are most easily prepared from 



