XVII. The Bakerian Lecture.—On the gaseous state of matter

Abstract

Since the investigation “On the Continuity of the Gaseous and Liquid States of Matter,” which formed the subject of the Bakerian Lecture for 1869, was communicated to the Society, I have continued to pursue the inquiry in a more extended form, with the view of discovering the general laws which determine the physical conditions of matter in the gaseous and liquid states. The subject in its whole extent and under all its aspects is so vast in itself, and its investigation in many cases has been surrounded by experimental difficulties of so high an order, that I must crave the indulgence of the Society if the amount of work actually accomplished appear small for the time devoted to it. I will give in the first place a few details regarding the method of mounting the apparatus, which will aid greatly any one who may hereafter desire to pursue the inquiry. The apparatus employed is, in all the essential parts, the same as that which I formerly described. The packing of the steel screw, by which the pressure is produced, is an important part of the operation. It is effected by means of a number of circular disks of leather, pierced centrally with a fine hole, and rendered impervious to water by being saturated in vacuo with melted lard. These disks are introduced, one by one, into a cylindrical cavity above the female screw in the lower end-piece, care being taken to press down each disk separately by a few gentle blows of a wooden mallet. After the introduction of the leather packing, the brass end-piece is placed with the face down­wards on a small wooden block, and the whole is firmly clamped to a steady bench or table. The steel screw is then inserted, and screwed through the leather packing till it enters into the wooden block. The connexion between the metal and glass tube in the upper end-piece is established by forming a protuberance on the glass tube accurately corresponding to a conical surface in the passage through the end-piece. The conical surface of the glass tube and the adjoining cylindrical surface for an inch and a half below the cone were covered with several layers of fine thread coated with ordinary shoemaker’s wax. The brass end-piece was gently heated before the introduction of the glass tube, and the latter was firmly fixed in its place by steady pressure. So perfectly have these arrangements fulfilled their purpose, that the apparatus, when successfully mounted, will remain in perfect order and without a trace of leakage for an indefinite period of time. The greatest pressure to which I have exposed the apparatus is 500 atmospheres, but it would be easy with very fine glass tubes to make accurate observations even at much higher pressures.