ADH 



ADI 



, pension of water in capillary tubes ; or, 

 lastly, between two fluids, as oil and wa- 

 ter. About the same time Mr. Hauksbee 

 proved experimentally the error which 

 Bernoulli had fallen into, in attributing 

 the adhesion of surfaces and capillary at- 

 traction to the pressure of the atmo- 

 sphere. Nevertheless, in 1772, M. M. 

 La Grange and Cigna, taking for granted a 

 natural repulsion between water and oily 

 substances, imagined, if there was an ad- 

 hesion between water and oil, or tallow, 

 that it must be occasioned by a cause dif- 

 ferent from attraction : and having ascer- 

 tained the reality of the adhesion, they 

 concluded that it was occasioned by the 

 pressure of the air, and that Dr. Taylor's 

 method was not well founded. 



Such was the state of opinions on the 

 subject, when, in 1773, Guyton Morveau 

 made his celebrated experiments on ad- 

 hesion, in presence of the Dijon Academy, 

 demonstrating, as indeed Hauksbee had 

 done before him, not only that water as- 

 cends between two parallel plates of tal- 

 low, separated from each other 1,8 of a 

 line, but also that the atmospheric pres- 

 sure is not in the least degree the cause of 

 the phenomenon, which is solely attribut- 

 able to attraction; in proof of this, a po- 

 lished disk of glass, 30 lines in diameter, 

 was suspended to the arm of a balance, 

 and brought into contact with the surface 

 ef mercury : the counterpoise required 

 to separate it was equivalent to 9 gros 

 and a few grains ; and upon moving the 

 apparatus into the receiver of an air- 

 pump, and forming as perfect a vacuum 

 as possible, precisely the same counter- 

 poise was required as before. 



In the prosecution of his inquiries on 

 this subject, he observed, that the same 

 disk of glass, which, when in contact with 

 pure water, adhered to it with a force 

 equal to 258 grains, required a counter- 

 poise of only 210, in order to separate it 

 from a solution of potash, notwithstanding 

 the superior density of this last. This 

 inequality of effects on equal diameters, 

 and in an inverse order to that of the 

 respective specific gravities of the two 

 fluids, appeared not only to be decisive in 

 favour of Dr. Taylor's method, but to en- 

 courage the hope of applying it to the 

 calculation of chemical affinities. 



In order to verify this proposition, 

 plates of the different metals in their 

 highest state of purity were procured, 

 perfectly round, an inch in diameter, of 

 the same thickness, well polished, and 

 furnished with a small ring in the centre 

 of each, so as to keep them suspended 



precisely parallel to the plane of the hori- 

 zon. Each of these plates was in turn 

 suspended to the arm of an assay balance, 

 and exactly counterpoised by weights 

 placed in the scale attached to the oppo- 

 site arm; the plate, thus balanced, was 

 applied to the surface of some mercury 

 in a cup, about two lines beneath it, by 

 sliding the plate over the mercury, as in 

 the silvering of mirrors, so as to exclude 

 every bubble of air ; weights were then 

 successively added, till the adhesion be- 

 tween the plate and the mercury was 

 broken. Fresh mercury was used for 

 each experiment. The following is the 

 table ot results : 

 Gold adheres to mercury with 



a force equal to .... 446 grains, 



Silver 429 



Tin 418 



Lead 397 



Bismuth 372 



/inc 204 



Copper 142 



Antimony (regulus) . . . 126 



Iron 115 



Cobalt 8 



The striking differences in the above 

 table shew that the pressure of the at- 

 mosphere has no share in them, since in 

 this respect the circumstances of each 

 were precisely similar ; nor do they de- 

 pend on the respective specific gravities; 

 for if so, silver should rank after lead, 

 cobalt before zinc, and iron before tin. 

 The only order which agrees with the 

 above is that of the chemical affinity of 

 these metals, or the respective degrees of 

 their solubility in mercury. It is highly 

 probable, therefore, that at least the prin- 

 cipal part of the adhesive force thus found 

 by experiment is owing to chemical affi- 

 nity ; and that the above numerical series, 

 446, 429, 418, 397, &c. is an approxima- 

 tion towards the ratio of the relative af- 

 finities of gold, silver, tin, lead, &c. for 

 mercury. 



ADIANTHUM, Maiden-hair, in botany, 

 the name of a genus of plants of the 

 Cryptogamia Filices class and order, the 

 characters of which are, that the fructifi- 

 cations are collected in oval spots at the 

 ends of the leaves, which are folded back. 

 There are forty -four species, of which one 

 only belongs to Great Britain, viz. the A. 

 capillus veneris, vrhich is found rarely in 

 Scotland and Wales, on rocks and moist 

 walls, and which is a native of the south 

 of Europe and the Levant. From this 

 the syrup of capillaire is made. Another 

 species, the Adianthum pedatum, was 

 formerly esteemed as a valuable article 



