3^ COHESION OF FLUIDS. 



Application of surface, WG must diminish this ordinate in the proportion of the 



particular ^'"^ °^ ^^° ^° *-^^ ^^"^ ^^ ^^°> ^^'^ '* ^^^^^ become .06, for the 

 fluids. actual depression in this case. The elevation of the mercury 



that adheres to the lower horizontal surface of a piece of glass, 

 and the thickness at which a quantity of mercury will stand 

 when spread out on glass, supposing the angle of contact still 

 ' 140°, are found, by taking the proportion of the sines of 20^ 



and of 70° to the sine of 45", and are therefore .0484 and 

 .1330 respectively. If, instead of glass, we employed any sur- 

 face capable of being wetted by mercury, the height of eleva- 

 tion would be .141, and this is the limit of thickness of awid6 

 surface of mercury supported by a substance wholly incapa- 

 ble of attracting it. Now the hydrostatic pressure of column 

 of mercury .0484 in thickness on a disc of one inch diameter 

 ■would be 131 grains; to this the surrounding elevation of the 

 fluid will add about 1 1 grains for each inch of the circumference, 

 with 'some deduction for the effect of the contrary curvature 

 of the horizontal section, tending to diminish the height; and 

 the apparent cohesion thus exhibited will be about l60 grains, 

 which is a little more than four times as great as the apparent 

 cohesion of glass and water. With a disc 1 1 hues in diameter 

 Mr. Dutour found it 194 French grains, which is equivalent to 

 152 English grains, instead of l60, for an inch, a result which 

 is sufficient to confirm the principles of the calculation. Tho 

 depth of a quantity of mercury standing on glass I have found 

 by actual observation, to agree precisely with this calculation.' 

 Segner says that the depth was .1358, both on glass and on 

 paper : the difference is very trifling, but this measure is some- 

 what too great for glass, and too small for paper, since it ap- 

 pears from Dutour's experiments, that the atration of papei' 

 to mercury is extremely weak. 



If a disc of a substance capable of being wetted by mercury, 

 an inch in diameter, were raised from its surface in a position 

 perfectly horizontal, the apparent cohesion should be 381 

 grains, taking .141 as the height: and for a French circular 

 inch, 433 grains, or 528 French grains. Now, in the experi- 

 ments of Morveau, the cohesion of a circular inch of gold to 

 the surface of mercury appeared to be 446 grains, of silver 

 429, of tin 418, of lead 397, of bismuth 37'i, of zinc 204, 

 of copper 142, of metallic antimony 126, of iron 115, of co- 

 balt 8 : and this order is the same with that in which ihe me- 

 tals 



