Mr. Faraday compressed carbonic acid gas into a liquid by the pressure of its own elasticity when disengaged from combination in close vessels, a force equal to the weight of thirty-five times that of our atmosphere; and the liquid was reduced to a solid by M. Thilorier by rapid evaporation, during which the heat was given out so quickly by one part of the liquid, that the remainder was condensed into a substance like snow, which could be touched with impunity, but when mixed with sulphuric ether its temperature was reduced to 166° below zero of Fahrenheit’s thermometer. Carbon appears naturally under a great variety of forms, and exhibits one of the most striking instances of allotropism, the same substance showing the greatest contrast in appearance and physical properties. The diamond, the most resplendent, transparent, and hardest of gems, is identical with carbon, which is black, dull, opaque, and brittle. Both are combustible; carbon is easily ignited, but it requires a heat of 1860° to consume the diamond. However numerous the crystalline forms assumed by substances either naturally or artificially may be, they are all capable of being grouped into geometrical systems; each system possessing its own allied and derivative forms capable of mutual variations among themselves, but the forms of one system never assuming those of the other. With that law, however, carbon and a few other substances are completely at variance. The diamond crystallizes in octohedrons, while graphite, which is also carbon, crystallizes in six-sided plates,—two forms that belong to different systems quite irreconcilable with one another: and thus carbon possesses the property of being dimorphous. Sulphur is a simple inflammable mineral abounding in volcanic countries, either in a crystalline or amorphous state, and forming a constituent in organic substances, animal and vegetable. It is readily dissolved by bisulphide of carbon, by benzine, and by a moderate heat; and copper filings exposed to its vapour spontaneously take fire, the chemical force of combination merging into light and heat. Sulphuretted hydrogen gas, a combination of sulphur and hydrogen, forms naturally during the putrefaction of organic matter, and Mr. Faraday observes with regard to the affinities of sulphur, ‘so numerous are its relations, so extensive its range of combinations, that we must consider it to be the very foundation on which chemical manufacture is built up.’ Though a simple substance, sulphur exhibits the two remarkable phenomena of dimorphism and the allotropic property. When reduced by heat to vapour and cooled slowly, it crystallizes in rhombic octohedrons; when merely melted and allowed to cool slowly, it takes the form of oblique rhombic prisms. Here the same atoms when in vapour and in a liquid state are acted upon by different forces; but however that may be, sulphur is another singular exception to the law of the immutability of the crystalline systems.