282 TITRIMETRIC METHODS 



0.5-30 /j.g. chloride is used. For more than 2 ^g. the error does not 

 exceed 0.5%, and for more than 0.5 fig. it does not exceed 2%. 



Since there is little difference between the two electrometric 

 methods, only that of Linderstr0m-Lang, Palmer, and Holter will 

 be described. It has a simple electrode system (the filled burette 

 serves as one half of the cell), and the titration can be carried out 

 in the glass reaction tube used for the ashing of the sample. Cun- 

 ningham et al. (1941) demonstrated that plasma can be titrated 

 directly, without ashing, by the electrometric method. Colorimetric 

 methods are given on pages 200 and 224. 



Linderstr^m-Lang, Palmer, and Holter Electrometric Method 

 for Chloride 



SPECIAL APPARATUS 



The arrangement of the titration set-up is illustrated in Figure 

 69. A and A' are silver wires that serve as electrodes. They are 

 connected to a potentiometer so arranged that the galvanometer 

 gives no deflection when the potential difference across the electrodes 

 is -f-210 millivolts, corresponding to a silver concentration in the 

 titration tube of 0.05 X 10^ M. This concentration would be ob- 

 tained by adding 0.013 fA. 0.02 A^ silver nitrate to the 50 /xl. liquid 

 employed in the titration tube. The burette, which is of the type 2 

 variety (Fig. 83, page 256) can be read to 0.02 [A. 



SPECIAL REAGENTS 



Ashing Solution. Dissolve 1.2 g. sodium nitrate and 0.4 g. secondary 

 sodium phosphate (Na2HP04.2H20) in water and make up to 

 14ml. 



0.10 N Nitric Acid. This soln. and the titration soln. below were 

 changed from 0.17 to 0.10 N nitric acid, as suggested by Linder- 

 str0m-Lang ( 1936) in a later publication. 



Titration Solution. Dissolve 0.3398 g. silver nitrate (0.02 N) in 

 100 ml. 0.10 N nitric acid containing 1.20 g. sodium nitrate and 

 0.40 g. secondary sodium phosphate (Na2HP04.2H20). 



PROCEDURE 



1. Place the tissue sample in a heat-resistant tube (Fig. 35, 

 page 167) containing 7 [x\. ashing soln. Evaporate the water in an 

 oven at 106°, and ash the material by careful heating in a flame. 



