[285] NOTE ON A SIMPLE GAS-CIRCULATING PUMP

Transcription

1 [285] NOTE ON A SIMPLE GAS-CIRCULATING PUMP BY W. LEACH (With 2 figures in the text) I N the course of designing an apparatus for investigating certain respiration problems, it was found that some form of pump was required for the purpose of circulating the gas in the system. The arrangement as described by Blackman and Bolas^^ was set up at first, but, although it was quite satisfactory and efficient in its working, it was felt that it would be an advantage if a pump of a more compact form could be devised. After some experimenting the apparatus shown in Fig. i was made and was found to possess certain advantages over the Blackman and Bolas type for our own particular purpose. The pump was made of glass, and its construction should present no difficulty to anyone moderately skilled in glass working. As will be seen, the pump consists essentially of a U-tube containing mercury, and having one arm considerably longer than the other. Connected with the shorter arm B, which constitutes the barrel of the pump, are two non-return valves of glass ground to glass seatings, and arranged in the usual way to allow of circulation of gas through the barrel in one direction only. These valves are made small in volume and of a form which avoids as far as possible the presence of pockets in which dead gas might hang. Floating on the mercury in each arm of the U-tube are hollow glass floats, shghtly smaller in diameter than the bore of the arms so that they move freely up and down as the level of the mercury changes. The one in the pump barrel arm B has a rounded top, so that when it moves upwards it displaces practicauy all the gas present inb. At the top of arm ^ is a side tube D, and a hollow, ground-in stopper C. This stopper has ground to it a release valve G with a long stem M which projects down below the rim of the stopper into the arm A. Float K has a flat top so that, when it is raised, it comes into contact with the valve stem M, and lifts the valve off its seating. 1 Annals of Botany, 40,

2 286 W. LEACH Fig. I

3 Note on a Simple Gas-Circulating Pump 287 Tube D is connected to an ordinary laboratory filter-pump as in the case of the Blackman-Bolas apparatus. When the filter-pump is operating the mercury in arm A rises until the float K strikes the release-valve stem M and lifts it. Air then enters past G and the mercury falls, to rise again almost immediately as air is again removed from A by the filter-pump. This alternate rise and fall continues so long as the filter-pump is in operation. The up and down movement is transmitted to the mercury and float in arm B which results in gas being pumped round from F to E in the ordinary way. Fig. 2 The advantages claimed for this apparatus over the Blackman- Bolas type are as follows: (1) Less mercury is required. (2) No splashing of mercury occurs. (3) There is less mercury in contact with the circulating gas. (4) The volume of circulating gas in the pump is small. (5) The action is more regular, the beats of the pump occurring at more frequent intervals. (6) The pump is quiet in working, the only noise being that due to the opening and closing of the valves. Although the pump shown in Fig. I is drawn to scale, its stze and

4 288 W. LEACH proportions may be varied to suit any particular rate of gas circulation that is required. The pump can be worked as described above, by simply connecting it to a filter-pump, the correct amount of suction for its operation being obtained by adjusting the water tap to which the filter-pump is attached. A more satisfactory method however is to fit it up as shown in Fig. 2. In this figure, the circulating pump B is shown connected by an india-rubber tube to a separating funnel A which is closed by a rubber bung. The separating funnel is connected to the filter-pump by means of the tube C. The air is removed from the separating funnel by the filter-pump, and the suction on the mercury in the circulating pump is adjusted by means of the screw-chp F. When this is done, and the circulating pump is working in its most satisfactory manner, it may be stopped and started again at will by simply turning the tap E off or on. The separating funnel also acts as a trap to catch any mercury that may be inadvertently sucked over when adjusting the clip F. This mercury can be drawn off by means of the tap G.

5