Dr. Murray entered the lists as the avowed partisan of the theory of Berthollet; Dr. Davy, on the other hand, appeared as the champion of his brother's doctrine. A severe contest ensued, and both combatants displayed equal skill and strength. The object of the former was to demonstrate the presence of water, or its elements, as a constituent part of muriatic acid; and he proposed to determine the point by combining the dry gases of muriatic acid and ammonia; for as these bodies did not contain its elements, should water appear, he maintained that it must be considered as pre-existing in the muriatic acid; while, on the contrary, if no water could be procured, it would be unphilosophical to suppose it present, but that muriatic acid gas must, in that case, be considered as a compound of hydrogen and chlorine. In performing this experiment, Dr. Murray did succeed in obtaining a portion of water; but the inference from such a fact was questioned on the other side, upon the assumption of the humidity of the gases. As all parties, however, seemed to agree, that if every source of error could be excluded, the combination of these gases would furnish an _experimentum crucis_, by which the truth or fallacy of either theory might be established, Davy, when at Edinburgh, was desirous of repeating the experiment with Dr. Hope, and it was accordingly made in the College Laboratory. Sir George Mackenzie, Mr. Playfair, and some other gentlemen, were present. The results were communicated in Nicholson's Journal by Dr. Davy, and may be briefly stated as follows:--The alkaline and acid gases were pure, and both had been previously dried by exposure for sixteen hours to substances having a strong attraction for water. The apparatus consisted of a plain retort of about the capacity of twenty-six cubic inch measures, with a stop-cock; and of a receiver, with a suitable stop-cock. The latter was filled over mercury with one of the gases, which from the receiver passed into the exhausted retort by means of the stop-cocks; the other gas was introduced the same way into the retort; and thus alternately about ninety cubic inches of each gas were combined. All the salt having then been driven into the bulb of the retort by the heat of a spirit lamp, the neck was cooled and kept cold by moistened cloths, whilst the bulb was heated by a coke fire, till the muriate began to sublime, and to make its appearance at the curvature of the vessel when the fire was withdrawn. The result was then examined, while the bottom of the retort was still very hot: a dew, just perceptible, was observed lining the cold neck. The quantity of water was so extremely small, that the globular particles composing this dew could scarcely be perceived by the naked eye; now the quantity of water, according to hypothesis, should equal no less than eight grains. There is no small difference, it must be confessed, between that quantity and a dew barely perceptible, and which may