Sulphuric acid -- 0.5 c.c. 20.0 c.c. "Hypo" required 20.4 c.c. 20.7 " 15.2 "[86] Nitric acid -- 0.5 c.c. 10.0 c.c. "Hypo" required 20.4 c.c. 21.5 " could not be titrated. In the application of this titration to the assay of manganese ores, hydrochloric and hydriodic acids are the only ones likely to be present. ~Effect of Alkalies.~--On theoretical grounds the presence of these is known to be inadmissible. A solution rendered faintly alkaline with ammonia required only 11.2 c.c. of "hypo;" and another, with 0.5 gram of caustic soda, required 4.0 c.c. instead of 20.4 c.c. as in neutral solutions. ~Effect of nearly Neutralising Hydrochloric Acid Solutions with Ammonia.~--Provided care is taken not to add excess of ammonia, this has a good effect, counteracting the interference of excess of acid. Thus 20 c.c. of iodine (as before) required 20.4 c.c. of "hypo;" with 15 c.c. of hydrochloric acid 20.7 c.c. were required, but with 15 c.c. of acid, nearly neutralised with dilute ammonia 20.4 c.c. were used. ~Effect of the Addition of Starch.~--The addition of varying quantities of starch has no effect, provided it is added when the titration is nearly finished, as the following experiments show:-- Starch added 1.0 c.c. 5.0 c.c. 10.0 c.c. 50.0 c.c. "Hypo" required 20.4 " 20.4 " 20.4 " 20.5 " But if the starch is added before the titration, the results are liable to error. Starch added 1.0 c.c. 50.0 c.c. "Hypo" required 20.4 " 24.0 " The starch should be used fresh, and is best made on the day it is used; after four days the finishing point is not so good. ~Effect of Varying Potassium Iodide.~--An excess of iodide is always required to keep the iodine in solution; a larger excess has little effect. Iodide added -- 1 gram 20 grams "Hypo" required 20.4 c.c. 20.5 c.c. 20.6 c.c. The 20 c.c. of iodine used, itself contained 0.5 gram of potassium iodide. ~Effect of Foreign Salts.~-- Bicarbonate of soda added -- 0.5 gram 1.5 gram 5.0 grams "Hypo" required 20.4 c.c. 18.2 c.c. 17.1 c.c. 16.0 c.c. The solution obviously must be free from bicarbonate of soda. This should be remembered, since when titrating arsenic assays with iodine it must be present; and students must avoid confounding the two titrations. In some other experiments, in which 10 grams each of the salts were taken, the following results were obtained:-- Salt added -- AmCl AmNO_{3} Am_{2}SO_{4} "Hypo" required 20.4 c.c. 20.5 c.c. 20.3 c.c. 20.2 c.c. Salt added NaCl NaNO_{3} Na_{2}SO_{4} "Hypo" required 20.3 c.c. 20.4 c.c. 20.4 c.c. ~Effect of Varying Iodine.~-- Iodine added 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c. "Hypo" required 1.3 " 10.2 " 20.4 " 51.0 " 102.0 "