“find something remarkable in the solution of _manganese_ in spirit of salt. Mr Woulfe, however, in a very friendly manner, at the same time, cautioned me with respect of the vapour that would issue from it, as from his own experience he apprehended it was of a very dangerous nature.... I cannot say that it was the apprehension of danger, but rather having other things in view, that prevented my giving much attention to the subject.” Priestley’s experiments led to no decisive result: he of course recognised the “peculiar smell, exactly resembling that which is procured by dissolving _red lead_ in the same acids.... On the application of heat it was easy to perceive that air, or vapour, was expelled; but it was instantly seized by the quicksilver.... This is a new field that is yet before me.” Priestley never occupied that field. It is tolerably certain that both Woulfe and he had unknowingly prepared _chlorine gas_, but the glory of its discovery belongs to Scheele. The paper “Of Sound in Different Kinds of Air” is worth quoting as showing Priestley at his best:— “Almost all the experiments that have hitherto been made relating to _sound_ have been made in common air, of which it is known to be a vibration, though it is likewise known to be capable of being transmitted by other substances. There could be little doubt, however, of the possibility of sound _originating_ in any other kind of air, as well as being _transmitted_ by them; but the trial had not been actually made, and I had an easy opportunity of making it. “Besides, the experiments promised to ascertain whether the _intensity_ of sound was affected by any other property of the air in which it was made than the mere _density_ of it. For the different kinds of air in which I was able to make the same sound, besides differing in specific gravity, have likewise other remarkable chemical differences, the influence of which with respect to sound would, at the same time, be submitted to examination.