Apprehending that the fixed air in the distilled water occasioned the coagulation, or separation of the oily part of the soap, only by destroying the causticity of the _lixivium_, and thereby rendering the union less perfect betwixt that and the tallow, and not by the presence of any acid; I impregnated a fresh quantity of the same distilled water with fixed air, which had passed through half a yard of a wide barometer-tube filled with salt of tartar; but this water caused the same curdling with soap as the former had done, and appeared in every respect to be exactly the same. EXPERIMENT IX. Distilled water saturated with fixed air formed a white cloud and precipitation, upon being mixed with a solution of _saccharum saturni_. I found likewise, that fixed air, after passing through the tube filled with alkaline salt, upon being let into a phial containing a solution of the metalic salt in distilled water, caused a perfect separation of the lead, in the form of a white powder; for the water, after this precipitation, shewed no cloudiness upon a fresh mixture of the substances which had before rendered it opaque. NUMBER II. _A Letter from Mr. HEY to Dr. PRIESTLEY, concerning the Effects of fixed Air applied by way of Clyster._ Leeds, Feb. 15th, 1772. Reverend Sir, Having lately experienced the good effects of fixed air in a putrid fever, applied in a manner, I believe not heretofore made use of, I thought it proper to inform you of the agreeable event, as the method of applying this powerful corrector of putrefaction took its rise principally from your observations and experiments on factitious air; and now, at your request, I send the particulars of the case I mentioned to you, as far as concerns the administration of this remedy. January 8, 1772, Mr. Lightbowne, a young gentleman who lives with me, was seized with a fever, which, after continuing about ten days, began to be attended with those symptoms that indicate a putrescent state of the fluids. 18th, His tongue was black in the morning when I first visited him, but the blackness went off in the day-time upon drinking: He had begun to doze much the preceding day, and now he took little notice of those that were about him: His belly was loose, and had been so for some days: his pulse beat 110 strokes in a minute, and was rather low: he was ordered to take twenty-five grains of Peruvian bark with five of tormentil-root in powder every four hours, and to use red wine and water cold as his common drink.