The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

EXPERIMENT XXXV. Of the Cause of Filtration, and the Rising of Wa∣ter in the Syphons, &c.

* 1.1TO try whether in Filtrations the rising of the Water might not proceed from the Impulse of the Air; we made use of a Syphon of Glass, represented by the Third Figure, which is made of two strait Pieces, and a crooked one, which joyns the other two together, the Jun∣ctures being well clos'd. The longer Leg of the Syphon was pervious only at the small End, so as to suffer the Water to pass through it; but

both the ends of the shorter Leg were equally pervious, the Diameter of their Bore being ¼ of an Inch. The length of these two Pipes was about a Foot and a half, that the Rarifi'd Air in the Receiver, when it was pretty well exhausted, might not raise the Water included in the Pipe too high. The shorter Leg of the Syphon be∣ing immers'd two or three Inches in a Vessel of Water, the other end was fastned to the Cover; which things being done, and the Receiver clos'd up, we began to pump. The Result of which was, that the Water dropp'd out of the lower Leg of the Syphon, as if it had been expos'd to the open Air; till the Receiver was in some measure exhausted, and then several Bubbles ri∣sing in the Water, gather'd together at the Top of the short leg'd Syphon, where expanding themselves, they stopp'd the Course of the Wa∣ter; that in the longer Leg being suspended in the Tube and ceasing to drop; and the Water in the shorter Leg, was so far depress'd, as not to be above a Foot high: But as soon as the Exter∣nal Air was let in again, it enter'd in at the small Orifice of the longer Tube; and, ascending through the Water contain'd in the Pipe, joyn'd with the former, which was lodg'd in the upper Part of the short leg'd Tube.

But, to prevent what Inconveniences ensu'd the rising of these Bubbles, the two foremen∣tion'd Tubes, were placed so, as to meet in the middle of a Glass Viol, the Neck of the Viol being clos'd up with Cement; and the Tubes be∣ing thus fix'd, and they, as well as the Viol, fill'd with Water, the Syphon represented by the Fifth Figure was plac'd in the Receiver with its

shorter Leg in a Vessel of Water, upon which the Pump being ply'd, the longer Syphon con∣tinu'd to drop much longer than before; but at the last, the Bubbles which rose in the Pipes, were so dilated in the Viol, as to press down into the Ends of the Tube, and interrupt our Experiment, tho' what we observ'd gave us Reason to believe, that the Air contributed to the Motion of the Water through the Sy∣phons.

And here, I shall subjoyn, that I once had a very slender Pipe, which when held upon the Surface of the Water in a Perpendicular Posture, the Incumbent Atmosphere press'd so much more on the Surface of the External Water, than that contain'd in the Tube, that the Water was rais'd in the Tube; and this Pipe being bent into a Sy∣phon, and plac'd with the shorter Leg in Water as Syphons usually are, the Water, of its own accord, rose up in the shorter Leg, and ran down the other; and this Syphon being plac'd in our Receiver, to try what Alteration of the Phaenomenon would appear there, we could not dis∣cern any sensible one. But tho' in this Tube just now mention'd, the Water rises of its own ac∣cord; yet, if such a Tube be thrust a little way into the Mercury, instead of rising, the Mer∣cury in the Tube will be below that which is without it.

Notes

• * 1.1

  The Cause of Filtration.