PHYSICAL PROPERTIES OE WATER, ETC. 9 



Now by placing this ball and tube under the receiver of an air-pump, I could see the 

 degree of expansion of the water, answering to any degree of rarefaction of the air ; and 

 by putting it into a glass receiver of a condensing engine, I could see the degree of 

 compression of the water, answering to any degree of condensation of the air. But 

 great care must be taken, in making these experiments, that the heat of the glass ball be 

 not altered, either by the coming on of moisture, or its going off by evaporation ; which 

 may easily be prevented by keeping the ball under water, or by using oil only in 

 working the pump and condenser. 



" In this manner I have found by repeated trials, when the heat of the air has 

 been about 50 degrees, and the mercury at a mean height in the barometer, that the 

 water will expand and rise in the tube, by removing the weight of the atmosphere, 

 4 divisions and ~ ; or one part in 21,740 ; and will be as much compressed under the 

 weight of an additional atmosphere. Therefore the compression of water by twice the 

 weight of the atmosphere, is one part in 10,870 of its whole bulk. 1 



" The famous Florentine Experiment, which so many philosophical writers have 

 mentioned as a proof of the incompressibility of water, will not, when carefully 

 considered, appear sufficient for that purpose : for in forcing any part of the water 

 contained in a hollow globe of gold through its pores by pressure, the figure of the gold 

 must be altered ; and consequently, the internal space containing the water, diminished ; 

 but it was impossible for the gentlemen of the Academy del Cimento to determine, that 

 the water which was forced into the pores and through the gold, was exactly equal to 

 the diminution of the internal space by the pressure." 



" By similar experiments made since, it appears that water has the remarkable 

 property of being more compressible in winter than in summer ; which is contrary to 

 what I have observed both in spirit of wine and oil of olives : these fluids are (as one 

 would expect water to be) more compressible when expanded by heat, and less so when 

 contracted by cold. Water and spirit of wine I have several times examined, both by 

 the air-pump and condenser, in opposite seasons of the year : and, when Fahrenheit's 

 thermometer has been at 34 degrees, I have found the water to be compressed by the 

 mean weight of the atmosphere 49 parts in a million of its whole bulk, and the spirit 

 of wine 60 parts ; but when the thermometer has been at 64 degrees, the same weight 



1 " If the compressibility of the water was owing to any air that it might still be supposed to contain, it is evident 

 that more air must make it more compressible ; I therefore let into the ball a bubble of air that measured near ^\ of an 

 inch in diameter, which the water absorbed in about four days ; but I found upon trial that the water was not more 

 compressed, by twice the weight of the atmosphere, than before." 



" The compression of the glass in this experiment, by the equal and contrary forces acting within and without the ball, 

 is not sensible : for the compression of water in two balls, appears to be exactly the same, when the glass of one is more 

 than twice the thickness of the glass of the other. And the weight of an atmosphere, which I found would compress 

 mercury in one of these balls but £ part of a division of the tube, compresses water in the same ball 4 divisions 

 and A-" 



(PHYS. CHEM. CHALL EXP. — PART IV. — 1888.) 2 



