ON THE COHESION OF FLUIDS. 



653 



ceed TTOo'' The experiments of Mr. Dutour 

 make the quantity of water raised equal to 

 44.1 grains for each square inch. Mr. 

 Achard found the force of adhesion of sulfu- 

 ric acid to glass, at 69° of Fahrenheit, 1.26, 

 that of water being 1, hence the height was 

 as .69 to 1, and its square as .47 to 1, which 

 is the corresponding proportion for the ascent 

 of the acid in a capillary tube, and which 

 does not very materially differ from the 

 proportion of .395 to I, assigned by Barruel 

 for this ascent. Musschenbroek found it .8 

 to 1, but his acid was probably weak. For 

 alcohol the adhesion was as .593, the height 

 as .715, and its square as .510 : the observed 

 proportion in a tube, according to an expe- 

 riment of Musschenbroek, was about .550, 

 according to Carre from .400 to .440. The 

 experiments on sulfuric ether do not agree 

 quite so well, but its quality is liable to very 

 considerable variations. Dutour found the 

 adhesion of alcohol .58, that of water being 1. 

 With respect to mercury, it has been 

 shown by Professor Casbois of Metz, and by 

 others, that its depression in tubes of glass 

 depends on the imperfection of the contact, 

 and that when it has been boiled in the tube 

 often enough to expel all foreign particles, 

 the surface may even become concave instead 

 of convex, and the depression be converted 

 into an elevation. Perhaps this changemay be 

 the effect of the commencement of a chemi- 

 cal action between the mercury and the com- 



ponent parts of the glass ; but in barometers 

 constructed according to the usual methods, 

 the angle of the mercury will be found to dif- 

 fer little from 140° : and in other experiments, 

 when proper precautions are taken, the in- 

 clination will be nearly the same. The de- 

 termination of this angle is necessary for find- 

 ing the appropriate rectangle for the curvature 

 of the surface of mercury, together with the 

 observations of the quantity of depression in 

 tubes of a given diameter. The table pub- 

 lished by Mr. Cavendish, from the experi- 

 ments of his father. Lord Charles Cavendish, 

 appears to be best suited for this purpose. 

 I have constructed a diagram, according to 

 the principles already laid down, for each 

 case, and I find that the rectangle v^iich 

 agrees best with the phenomena is .01. The 

 mean depression is always .015, divided by 

 the diameter of the tube : in tubes less than 

 half an inch in diameter, the curve is very 

 nearly elliptic ; and the central depression in 

 the tube of a barometer may also be found by 

 deducting from the corresponding mean de- 

 pression the square root of one thousandth 

 part of its diameter. There is reason to sus- 

 pect a slight inaccuracy towards the middle 

 of Lord Charles Cavendish's Table, from a 

 comparison with the calculated mean depres- 

 sion, as well as from the results of the me- 

 chanical construction. The ellipsis approach- 

 ing nearest to the curve may be determined 

 by the solution of a biquadratic equation. 



Diameter Grains in Mean depres- Central deprcs- Centra! de- Central de- Marginal de- 



in inches, an inch. sion by cal- sion by ob- pression by pression by jjression by 



C. culation. Y. serration. C. formula.Y. diagram. Y. diagram. Y. 



.0 



,5 



.4 



.35 



.30 



.as 



.20 

 .IS 

 .10 



972 

 67s 



432 

 331 

 343 

 1(S9 

 108 

 61 



S7 



.025 

 .030 

 .037 

 .043 

 .050 

 .080 

 .075 



.100 



.liO 



