PHOSPHORUS AND CHLORIDE 281 



characterizing the colorimetric procedures (page 226), and, since 

 the former methods do not offer sufficient compensating advantages 

 in accuracy, in the opinion of the writer, the colorimetric methods 

 deserve preference. 



CHLORIDE 



In chronological order, the following methods have appeared for 

 the determination of chloride in very small amounts of biological 

 material. 



Linderstr0m-Lang, Palmer, and Holter ( 1935) described an elec- 

 trometric titration method that can be carried out with a precision of 

 0.02 ju,l. 0.02 A^ silver nitrate. The sample for analysis should contain 

 preferably 0.4-2.0 fig. chlorine. For use on tissue, a preliminary 

 ashing procedure was employed which could be conducted in the 

 titration tube itself to avoid transfer. 



Conway (1935) employed a method based on oxidation of the 

 chloride to chlorine by an acid permanganate reagent, absorption 

 of the chlorine by potassium iodide solution, and estimation of the 

 iodine liberated by either titration or colorimetry, depending on the 

 quantity present. The reaction is made to take place in a diffusion 

 cell. Conway reported that, for quantities of chloride corresponding 

 to about 0.3 mg. chlorine, the coefficient of variation for a single 

 determination is 0.5%. Down to 7 ju,g. chlorine the coefficient of 

 variation increases to 4-5%, and when the method is adapted to 

 0.7 fxg. the coefficient of variation becomes 6—7%. 



Wigglesworth ( 1937) used a method based on addition of excess 

 silver nitrate, filtration, and back-titration with thiocyanate. The 

 method is applicable to as little as 0.3 jul. tissue fluid and the 

 precision is ±: 6%. Dean (1941) modified the Wigglesworth method 

 and carried out the reaction and titration in a drop placed on a 

 waxed slide. 



Cunningham, Kirk, and Brooks (1941) described an electrometric 

 titration method similar to that of Linderstr0m-Lang, Palmer, and 

 Holter (1935). A shallow dish is employed as the titration vessel 

 and silver-silver amalgam electrodes, a stirring needle, and the 

 burette tip all dip into the solution. To determine the end point of 

 the titration, the volume of standard silver nitrate solution added 

 is plotted against the resulting E.M.F. values. A sample containing 



