The product obtained by passing sparks through air in this manner turned litmus red, and gave rise to no cloud in lime-water, while the air was reduced to two-thirds of its original volume; nor did the lime-water give a precipitate on introducing some fixed air, this showing that it had been saturated by an acid. It was found, too, that “soap-lees,” or solution of caustic potash, if present, diminished the volume more rapidly than did lime-water; and repeated trials proved that “when five parts of pure dephlogisticated air were mixed with three parts of common air, almost the whole of the air was made to disappear.” The nitrate of potassium thus produced caused paper soaked in it and dried to deflagrate; and it contained no sulphuric acid. “There is no reason to think that any other acid entered into it except the nitrous.” But it gave a precipitate with silver nitrate; and Cavendish, suspecting that this was silver nitrite, prepared some potassium nitrite by heating the nitrate; on comparing the white precipitate which this solution gave with silver nitrate with that obtained from his “soap-lees,” he found them identical. There was therefore no “muriatic acid” present, which would have yielded chloride of silver, of appearance somewhat similar to the nitrite. As it had previously been shown to be probable that phlogisticated air is nitrous air united with phlogiston, and that nitrous air is nitric acid united with phlogiston, “we may safely conclude that in the present experiments the phlogisticated air was enabled, by means of the electric spark, to unite to, or form a chemical combination with, the dephlogisticated air, and was thereby reduced to nitrous acid, which united to the soap-lees and formed a solution of nitre; for in these experiments the two airs actually disappeared, and nitrous acid was actually formed in their room”. “A further confirmation of the above-mentioned opinion is that, as far as I can perceive, no diminution of air is produced when the electric spark is passed either through pure dephlogisticated air or through perfectly phlogisticated air, which indicates a necessity of a combination of these two airs to produce the acid. Moreover, it was found in the last experiment that the quantity of nitre procured was the same that the soap-lees would have produced if saturated with nitrous acid; which shows that the production of the nitre was not owing to any decomposition of the soap-lees.” Nothing more clearly shows the care with which Cavendish reasoned than these last quotations. No loophole is left unstopped; every precaution is taken to make the proof as faultless as it is possible for a proof to be. But this was not enough. It was necessary for Cavendish to show that, so far as he could ascertain it experimentally, _all_ the phlogisticated air was capable of combining with dephlogisticated air to form nitre. This he next proceeded to do.