We next take a bottle which holds eight or ten pints, the capacity of which is very accurately determined by weighing the water it is capable of containing. This bottle is turned bottom upwards, full of water, in the cistern of the pneumato chemical apparatus GHIK, Fig. 1. and is set on its mouth upon the shelf of the apparatus, instead of the glass jar V, having the extremity 11 of the tube 7, 8, 9, 10, 11, inserted into its mouth. The machine is fixed at zero of pressure, and the degree marked by the index 30 upon the sector m l is accurately observed; then, by opening the stop-cock 8, and pressing a little upon the jar A, as much air is forced into the bottle as fills it entirely. The degree marked by the index upon the sector is now observed, and we calculate what number of cubical inches correspond to each degree. We then fill a second and third bottle, and so on, in the same manner, with the same precautions, and even repeat the operation several times with bottles of different sizes, till at last, by accurate attention, we ascertain the exact gage or capacity of the jar A, in all its parts; but it is better to have it formed at first accurately cylindrical, by which we avoid these calculations and estimates. The instrument I have been describing was constructed with great accuracy and uncommon skill by Mr Meignie junior, engineer and physical instrument-maker. It is a most valuable instrument, from the great number of purposes to which it is applicable; and, indeed, there are many experiments which are almost impossible to be performed without it. It becomes expensive, because, in many experiments, such as the formation of water and of nitric acid, it is absolutely necessary to employ two of the same machines. In the present advanced state of chemistry, very expensive and complicated instruments are become indispensibly necessary for ascertaining the analysis and synthesis of bodies with the requisite precision as to quantity and proportion; it is certainly proper to endeavour to simplify these, and to render them less costly; but this ought by no means to be attempted at the expence of their conveniency of application, and much less of their accuracy. SECT. III. _Some other methods of measuring the volume of Gasses._ The gazometer described in the foregoing section is too costly and too complicated for being generally used in laboratories for measuring the gasses, and is not even applicable to every circumstance of this kind. In numerous series of experiments, more simple and more readily applicable methods must be employed. For this purpose I shall describe the means I used before I was in possession of a gazometer, and which I still use in preference to it in the ordinary course of my experiments.