The following experiments show the effect of variations in the conditions of the assay. A solution of stannous chloride equivalent in strength to the "permanganate" was made by dissolving 19.06 grams of the crystallised salt (SnCl_{2}.2H_{2}O.) in 50 c.c. of water and 10 c.c. of hydrochloric acid and diluting to 1 litre with water freed from dissolved oxygen. 100 c.c. contain 1 gram of tin. In the first experiments tap water was used and no precautions were taken for excluding air. Except when otherwise stated, 20 c.c. of the stannous chloride were used in each experiment with 10 c.c. of hydrochloric acid, and were diluted to 100 c.c. with water before titration. ~Effect of Varying Hydrochloric Acid.~ Acid added 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. "Permanganate" required 18.8 " 18.9 " 18.8 " 18.8 " The only effect of the increase in quantity of acid was to give the brown of perchloride of manganese instead of the pink of permanganic acid to mark the finishing point. ~Effect of Varying Temperature.~ Temperature 15° C. 50° C. 70° C. 100° C. "Permanganate" required 18.8 c.c. 18.7 c.c. 18.6 c.c. 18.4 c.c. ~Rate of Atmospheric Oxidation.~--Solutions ready for titration were exposed to air at the ordinary temperature for varying lengths of time and then titrated. Time exposed 0 min. 5 min. 10 min. 20 min. 60 min. "Permanganate" required 18.8 c.c. 18.8 c.c. 18.8 c.c. 18.8 c.c. 18.6 c.c. It is best to titrate at once, although the loss by oxidation is only small after one hour's exposure. ~Effect of Varying Tin.~ Stannous chloride added 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c. "Permanganate" required 0.7 " 8.8 " 18.0 " 47.4 " 95.4 " ~Effect of Varying Bulk.~ Bulk 50.0 c.c. 100.0 c.c. 200.0 c.c. 500.0 c.c. "Permanganate" required. 9.0 " 18.3 " 17.4 " 15.1 " The two last series show an interference, which is due to the oxygen dissolved in the water, as may be seen from the following similar experiments, which were, however, performed with water freed from oxygen and in which the titrations were effected in an atmosphere of carbonic acid. ~Effect of Varying Tin.~--A new solution of stannous chloride was used. Stannous chloride added 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c. "Permanganate" required 1.0 " 10.0 " 19.8 " 49.6 " 99.3 " ~Effect of Varying Bulk.~ Bulk 30.0 c.c. 50.0 c.c. 100.0 c.c. 200.0 c.c. 500.0 c.c. "Permanganate" required 19.8 " 19.8 " 19.8 " 19.8 " 19.8 " It will be seen that in working under these conditions the results are proportional and the method satisfactory.