THE DETERMI.NATIOX OF RADIOIROX 653 



ing the aluminum dish under the Geiger counter. Since the 500 micro- 

 gram of iron are about equally distributed over a surface of 1.2 cm- 

 we are measuring the radioactivity of an almost infinitely thin iron 

 layer. The intensity of the /3-radiation emitted by ^^Fe is reduced to half 

 its value when passing a layer of 10.0 mgm of aluminum per cm^. 



A few examples of the method described are given in Table I which 

 contains data on added and recovered amounts of ^^Fe obtained when 

 preparing "standard" samples. 



Since the procedure is rapid and easy to carry out and requires no 

 special equipment but a Geiger counter, it can be used in most clinical 

 laboratories. The accuracy obtained in clinical application of the method 

 is seen from Tables 2 and 3. Duplicate determinations involving both 

 combustion and counting technique are stated. 



Summary 



A simple and rapid method for the determination of ^"Fe is described. The 

 radioiron is precipitated as FeS and after filtration of the solution counted on 

 the filter paper. 



References 



P. F. Hahn, W. F. Bale, E. O. Lawrence and G. H. Whipple (1939) Radio- 

 active iron and its metabolism in anaenia. Its absorption, transportation and 

 utihzation. J. Exptl. Med. 69, 739. 



P. F. Hahn and W. M. Balfour (1942) Radioactive iron used to study red blood 

 cells over long periods. The constancy of the total blood volume- in the dog. 

 Am. J. Physiol. 135, 600. 



