CHLORIDES.
A normal and variable constituent of urine, chlorine, is not usually required to be determined. Should the estimation be considered necessary, however, Volhard's silver process, which has been noticed in treating of uric acid, possesses several advantages over other methods: 10 c.c. of urine are diluted with 60 c.c. of distilled water. To this is added 2 c.c. of pure 70 percent. nitric acid and 15 c.c. of a standard solution of silver nitrate (1 c.c. = 0.01 gramme NaCl). Shake well and make up to 100 c.c. with water. All the chlorine present will now be precipitated in the liquid as a silver salt. Filter an aliquot part (about 70 or 80 c.c.), and determine in the clear solution the excess of silver with standard ammonic thiocyanate, using the ferric alum indicator. The difference between this and the amount of silver originally present in the aliquot part has been precipitated as silver chloride (AgCl). The whole estimation should be conducted as rapidly as possible. A simple calculation will then give the proportion of chlorine in the dilute urine, and this multiplied by ten shows the percentage. It is usual to report in terms of NaCl.