A System of Blood Analysis.* Supplewent Ii. Simplified Method for the Determination of Chlorides in Blood or Plasma

The method of preparing protein-free filtrates by the use of tungstic acid, as developed and used by Folin, has proved so highly satisfactory in the determination of a number of blood constituents, that it has seemed desirable to apply it to the determination of chlorides. The procedure developed for this purpose is based upon the principle of the Volhard method;l namely, the precipitation of silver chloride from a known amount of silver nitrate and titration of the excess silver nitrate by means of sulfocyanate, using ferric ammonium alum as an indicator. A number of preliminary experiments were conducted to ascertain the most convenient conditions which would give a good end-point. Efforts to obtain increased accuracy by greatly increased dilution of reagents were disappointing. In order to insure a sharp end-point, the volume of fluid at the end of titration must be kept small, which cannot be done when very dilute solutions are used. As a result of dilution the end-point tends to be yellowish, rather than red, and cannot be accurately perceived, at least by the writer’s eye, except in strong daylight. This difficulty in the use of very dilute solutions is somewhat increased by the presence of oxalate, because of the lemon-yellow color of