The first two of these filtered badly, the precipitate coming through the filter; the last was very satisfactory in the working.
Effect of Varying Bulk.—Using 20 c.c. of lead nitrate, and 10 grams of sodium acetate as before, diluting to the required bulk, heating to boiling, and titrating, the results were:—
| Bulk | 100.0 | c.c. | 200.0 | c.c. | 500.0 | c.c. | 1000.0 | c.c. |
| "Chromate" required | 19.6 | " | 19.3 | " | 19.4 | " | 19.4 | " |
Effect of Varying Acetic Acid.—Since the experiments are carried out in the presence of sodic acetate, acetic acid is the only acid whose effect need be considered. Working as before, but with 200 c.c. bulk and varying amounts of the acid, the results were:—
| Acid present | — | 10.0 | c.c. | 20.0 | c.c. | 40.0 | c.c. |
| "Chromate" required | 19.7 c.c. | 19.1 | " | 18.5 | " | 17.3 | " |
These experiments show that only slight quantities of acid are admissible.
Effect of Varying Sodium Acetate.—With the same conditions as before, but with varying weights of sodium acetate, the results were:—
| Sodium acetate present | — | 5 grams | 10 grams | 25 grams | 50 grams |
| "Chromate" required | 19.7 c.c. | 19.6 c.c. | 19.6 c.c. | 18.8 c.c. | 17.8 c.c. |
These experiments show that excessive quantities of sodium acetate must be avoided. Ammonium acetate interferes to a greater extent, and if both acetic acid and this salt are present, each exerts its disturbing influence. With 10 grams of ammonium acetate, 19.4 c.c. of the chromate solution were required instead of 19.7 c.c. in the absence of this salt; with 10 grams of the acetate and 10 c.c. of acetic acid, only 18.6 c.c. were required.
Effect of Foreign Salts.—As already stated, sulphates interfere. Twenty c.c. of the lead nitrate solution were taken, precipitated with sulphate of soda, and the precipitate dissolved in 10 grams of sodium acetate and titrated as before. Duplicate experiments required 18.6 c.c. and 18.7 c.c. of the chromate solution. A similar experiment with 40 c.c. of lead nitrate required 37.4 c.c. of chromate. If the sulphate had not been present, the results would have been 19.7 c.c. and 39.4 c.c. respectively.