He then leaves the consideration of this gas, and attacks the unknown globules, which probably did not present any metallic appearance under the circumstances in which he saw them, for they must have been as minute as grains of sand. I rather think that he commenced his examination by introducing a globule of mercury, and uniting it with a globule of the unknown substance, for his note says, "Action of the substance on Mercury,--forms with it a solid amalgam, which soon loses its _Alkaligen_ in the air." And from the note which succeeds, he evidently considered this _Alkaligen_ (potassium) volatile, as he says "it soon flies off on exposure to the air." October 19.--It is probable that, in consequence of the property which the unknown substance displayed of amalgamating with mercury, he devised his experiment of the 19th. He took a small glass tube, about the size and shape of a thimble, into which he fused a platinum wire, and passed it through the closed end. He then put a piece of pure potash into this tube, and fused it into a mass about the wire, so as entirely to defend it from the mercury afterwards to be used. When cold, the potash was solid, but containing moisture enough to give it a conducting power; he then filled the rest of the tube with mercury, and inverted it over the trough: the apparatus being thus arranged, eurêka he made the wire and the mercury alternately positive and negative. And now, conceiving that I have sufficiently explained his brief notes, the reader shall receive the result in his own words: for this purpose I have obtained an engraving of the autograph, which is here annexed; but as it may not be very readily deciphered, I shall first give the substance of it in print.--"When potash was introduced into a tube having a platina wire attached to it--so--and fused into the tube so as to be a conductor, _i. e._ so as to contain just water enough, though solid, and inserted over mercury, when the platina was made negative, no gas was formed, and the mercury became oxydated, and a small quantity of the _alkaligen_ was produced round the platina wire, as was evident from its quick inflammation by the action of water. When the mercury was made the negative, gas was developed in great quantities from the positive wire, and none from the negative mercury, and this gas proved to be pure oxygene--A CAPITAL EXPERIMENT, PROVING THE DECOMPOSITION OF POTASH." The Reviewer of the Institution Journal well observes that those who knew Davy will best conceive the enthusiasm with which this hasty record of his success was dashed off, and will instantly recognise [Greek: eurêka] in his "CAPITAL EXPERIMENT." From this same Register, it appears that, in the preceding month, he was deeply engaged in experiments on '_Antwerp blue_,' which he found to consist of _Prussiate of Iron_ and _Alumina_, "probably in the proportion of two-thirds of the former to one-third of the latter."