MANOMETERS.--Make choice of a tube nearly capillary, very regular in the bore, and with sides more or less thick, according to the degree of pressure which it is to support. Seal this tube at one end, blow a bulb with thick sides near the middle, and curl it in S, just as is represented by pl. 2, fig. 9. For manometers which serve to measure the elasticity of the air under the receiver of the air-pump, what is generally employed is a tube closed at one end and bent into a U. Pl. 2, fig. 10. You should take care to contract these at some distance from the sealed part, in order to avoid the breaking of the instrument on the sudden admission of air. Manometers are graduated, as will be explained in the sequel. * * * * * MARIOTTE’S TUBE.--This is represented by pl. 2, fig. 7. It consists of a tube thirty-nine inches long, closed at one end, bordered and widened at the other, and bent into a U at the distance of eight inches from its sealed end. The graduation of this instrument will be described hereafter. * * * * * PHOSPHORIC FIRE-BOTTLE.--This is a short piece of tube closed at one end, and widened and bordered at the other, in such a manner as to receive a cork. Pl. 3, fig. 34. It is in this little vessel that the phosphorus is enclosed. Glasses of this form can be employed in a great variety of chemical experiments. * * * * * PULSOMETER.--This instrument consists of a tube, of which each extremity is terminated by a bulb; it is partly filled with nitric ether, and sealed at the moment when the ebullition of the ether has chased the atmospheric air wholly from the interior of the vessel. Pl. 2, fig. 16. * * * * * PUMP.--Solder a cylinder, B (pl. 4, fig. 12), to the extremity of a small tube, C, and form their point of coincidence into a funnel, to which you will adapt a valve. Pierce the wide tube or body of the pump at D, and solder there a piece of tube bent into an elbow and widened at the other end into a funnel, which is to be furnished with a second valve, as is represented in the figure. Prepare then the fountain of compression E, and, by means of a cork and a little sealing-wax, fix it upon the branch D. To prepare the piston, A, blow a bulb at the end of a tube, flatten the end of the bulb, and choke it across the middle, in order to form a place round which tow can be twisted, to make it fit the tube air-tight. Finish the piston by twisting the other end of the tube into a ring, as at A. The valves are formed of small cones of cork, or wood, having in the centre an iron wire of sufficient size and weight to enable them to play well. * * * * *