The Fourth Experiment: The Production of a Vacuum through the Extraction of Water from a Glass Vessel

Abstract

Because, as we have just said, some air always seemed to remain above the water in the glass (although, to be sure, it was not even a thousandth part of the evacuated glass), I devised another method of extraction. I procured a glass (commonly called a “viale”), which had a globe or retort at one end and at the other, a long neck (so that the water, through its own weight, might descend more easily from the globe). To this I had a metal cap with a stop-cock attached, as described above. This can be seen in the Plate. I filled the entire glass with water to the opening of the stop-cock and inserted it in the small tube of the apparatus, mn. When the pump operated, I saw that water, indeed, descended into the pump but that soon a sizeable bubble rose up through the glass tube. I perceived that this was air that had been concealed in the key of the stop-cock, (for usually the keys of spigots are cast hollow and are filled inside with gravel and sand instead of metal). Thus it was necessary that a stopcock be designed in such a way that its key be cast of solid bronze and then perforated.