A continuation of new experiments physico-mechanical, touching the spring and weight of the air and their effects. The I. part whereto is annext a short discourse of the atmospheres of consistent bodies / written by way of letter to the right honourable the Lord Clifford and Dungarvan by the honourable Robert Boyle ...

EXPERIMENT XII.

About the differing Heights whereto Liquors will be elevated by Suction, according to their several Specifick Gravities.

IF, when I was making the foregoing Experiment, I had been able to procure a Pipe long enough, I had tried to what height I could raise Water by Suction, though I would have done it ra∣ther to satisfie Others then my self, who scarce doubted, but that as Water is (bulk for bulk) about 14 times lighter than Quick-silver: so it would have been rais'd by Suction to about four or five and thirty foot, (which is 14 times as high as we were able to elevate the Quick-silver,) and no higher. But being not furni∣shed for the Tryal I would have made, I thought fit to substitute another, which would carry the former Experiment somewhat further. For whereas, in That, we shew'd how high the Atmo∣sphere was able by its whole Gravitation to raise Quick-silver; and whereas likewise that, which appears in Monsieur Paschals Ex∣periment, is, at what height the whole weight of the Atmosphere can sustain a Cylinder of Water: by the way that I thought on, it would appear, (which hath not yet (that I know of) been shewn,) how a part of the Pressure of the Air would in perpendicular Pipes raise not onely the two mentioned Liquors, but others also to Heights answerable to the degree of Pressure, and proportiona∣ble to the specifick Gravities of the respective Liquors.

To make this Tryal the more clear and free from exceptions, I caus'd to be made and inserted to the shorter Leg of the above mentioned Exhausting Siphon a short Pipe; which brancht it self equally to the right hand and the left,* 1.1 as the adjoyning Figure declares. In which contrivance I aim'd at these two convenien∣ces: one that I might exhaust two Glass-Canes at the same time; and the other, to prevent its being surmis'd that the Engine was not equally applied to both the Glasses to be exhausted. This

additional Brass-pipe being carefully cemented into the Sucking Syphon, we did to each of its two branches take care to have well fastned with the same Cement a Cylindrical Glass of about 42 Inches in length, (that being somewhat near the height of our ex∣hausting Syphon above the floor,) the lower Orifice of one of these two Glasses being immerst in a vessel of stagnant Mercury, and that of the other in a vessel of Water, where care was taken by those I imploy'd, that as the Tubes were chosen near of a bigness, (which yet was not necessary,) so the surfaces of the two different Liquors should be near of a height. This being done, we began to pump warily and slowly, till the Water in one of the Pipes was elevated to about 42 inches, and then measuring the height of the Quick-silver, in the other Pipe above the surface of the Stag∣nant Quick-silver, we found it to be almost 3 Inches; so that the Water was about 14 times as high as the Quick-silver. And to prosecute the Experiment a little further, we very warily let in a little Air to the Exhausting Syphon, and had the pleasure to see the two Liquors proportionably descend, till turning the Stop-cock when the Water was about 14 inches high, we thereby kept them from sinking any lower, till we had measured the height of the Quick-silver, which we found to be about one inch.

We tried also the proportion of these two Liquors at other heights, but could not easily measure thē so well as we did at those newly mentioned; and therefore though there seem'd to be some slight variation, yet we lookt upon it but as what might be well imputed to the difficulty of making such Experiments exactly; and this displeas'd me not in these Tryals, that whereas it was ob∣serv'd, and somewhat wondred at, that the Quick-silver for the most part seem'd to be somewhat (though but a very little) high∣er then the proportion of 1 to 14 required, I had long before by particular Tryals found, that though 14 and 1 be the nearest of small integer numbers that express the proportion between the Specifick Gravities of Quicksilver and Water, yet the former of those Fluids (or at least that which I made my Tryals with) is not

quite so heavy as this proportion supposes, though I shall not here stay to determine precisely the difference, having done it in another Tract, where the method I imployed in the investigation of it is also set down.

The above mentioned Experiment, made by the help of our Engine, as to Quick-silver and Water being confirmable by Try∣als (to be by and-by mentioned) made in other Liquors, affords our Hypothesis two considerable advantages above the vulgar do∣ctrine of the Schools, (for I do not apply what follows to all the Plenists,) who ascribe the ascension of Liquors by Su∣ction to a Traction made ob fugam vacui, as they are wont to speak.

For first it is manifestly agreeable to our Doctrine, that, since the Air, according to It, is a Fluid that is not void of Weight, it should raise those Liquors that are lighter, as Water, higher then those that are ponderous, as Quick-silver; and that answerably to the disparity of their Weights▪ And secondly, there is no rea∣son why, if the Air be withdrawn by Suction from Quick silver and Water, there should be less left a vacuum above the one then above the other, in case either of them succeed not in the place de∣serted by the Air, and consequently when the Air is withdrawn out of both the forementioned Glass-pipes, if there would be no vacuum in case no liquor should succeed it, why does Nature needlesly to prevent a vacuum make the Water that is an heavy body ascend contrary to its own nature, according to which it tends towards the Center of the Earth? And if the succeeding of a li∣quor be necessary to prevent a vacuum, how chance that Nature does not elevate the Quick-silver as well as the Water, especially since tis manifest by the foregoing Experiment that she is able to raise that ponderous Liquor above 26 inches higher than she did in the Experiment we are now discoursing of.

Perhaps it would not be amiss to take notice, on this occasion, that among other applications of this Experiment it may be made somewhat useful to estimate the differing Gravities of liquors, to

w^ch purpose I caus'd to be put under the bottom of the foremen∣tioned Glass pipes two vessels, the one with fresh water, & the other with the like water impregnated with a good proportion of Sea∣salt that I had caus'd to be dissolv'd in it, for want of Sea-water, which I would rather have imploy'd. And I found, that when the fresh water was rais'd to about 42 inches, the Saline solution had not fully reacht to 40.

But though this difference were double to that which the pro∣portion and Gravity betwixt our Sea-water and fresh water would have required, yet to make the disparity more evident, and also because I would be able the better to guess at the proportion of the dissolv'd Salt by making it as great as I could, I caus'd an un∣usual Brine to be made, by suffering Sea-salt to deliquate in the moist Air. And having applyed this Liquor and fresh water to the two already mentioned Pipes, and proceeded after the former manner, we found that when the pure water was elevated to near 42 Inches, the liquor of Sea-salt wanted about 7. Inches and a quarter of that height; and when the water was made to subside to the middle of its Pipe, or thereabouts, the Saline liquor in the other Pipe was between 3 and 4 inches lower then it.

I would have tryed the difference between these Liquors and Oyl, but the Coldness of the Weather was unfavourable to such a Tryal: but to shew a far greater Disparity then That would have done betwixt the height of Liquors of unequal Gravities, I took fair Water, and a liquor made of the Salt of Pot-ashes suffered to run in a Sellar per deliquium, (this being one of the ponderousest Liquors I have prepar'd,) and having proceeded as in the former Tryals, I found that when the common Water was about 42 inches high, the newly mention'd Solution wanted somewhat of 30 inches; and when the Water was made to subside to the mid∣dle of its Pipe, or thereabouts, the deliquated Liquor was between 6 and 7 inches lower then it.

I had some thoughts, when I applied my self to make these Tryals, to examine how well we could by this new way compare

the Saltness of the waters of several Seas, and those also of Salt∣springs; and likewise whether, and (if any thing near) how far we might by this Method determine the proportion of the more sim∣ple Liquors that may be mingled in compounded ones, as in the mixture of Water and Wine, Vinegar and Water, &c. but being not provided with Instruments fit for such nice Tryals, and a mis∣chance having impair'd the Glasses lately mentioned before the last Tryals were quite ended, and having soon after broken one of them, I laid aside those Thoughts.

Notes

• * 1.1

  Plate the Fig. the