Recently in the process of performing a determination of the serum chloride level by an application of the Volhard method on the blood of a patient who had received 500 ml. of dextran solution, a cloudy filtrate was obtained at that stage of the procedure in which the silver chloride precipitate is removed. Filtration is a necessary modification if an end point that is reproducible is to be obtained. Without filtration the end point fades rather quickly owing to the fact that silver chloride is more soluble than silver sulfocyanate and therefore reacts with the sulfocyanate:
AgCl + SCN- = AgSCN + Cl-
The principle of filtration is supported by Peters and Van Slyke.
Cloudy filtrates resulted at the same step during repeated determinations of the serum chloride on the blood of this patient for seven days and on the blood of a second patient with a different clinical condition