On the Motions of Camphor and Odorant Bodies. ^j 



fcrved, that the oil of camphor, as well as all the other oils, have a greater attra£l:lon than 

 water for the furface of the plate. In faft, Venturi obferved, and the fame remark was 

 afterwards made by rayfelf, that the part of the plate whence the water has retreated when 

 touched with a fmall piece of camphor, or any body dipped in volatile oil, remains var- 

 niftied with a coat of very fubtile oil, which is perceptible by the eye * ; whence he rightly 

 concluded, that the water retires to obey its affinity of aggregation, which becomes free 

 from the attraftion of the furface of the plate as foon as that furface is occupied by the oil ; 

 and this efFeft happens only becaufe this affinity of aggregation or cohefion has become 

 greater than the attraftion of the water to the plate. This is fo true that the fame phe- 

 nomenon always occurs, whatever oil be employed, whether volatile and odoriferous, or 

 not, fuch as oil of olives or lintfeed. As foon as the wet plate is touched with the finger 

 flightly dipped in one of thefe oils, the water retreats in a circle, as if it were touched 

 with any odoriferous body. 



There is doubtlefs, as Cit. Venturi has obferved, a ftronger attradion between the oil 

 and the furface of the plate, than between the latter and the water; which is evidently 

 proved by the obfervations : let a drop of olive, or any other fixed oil, be dropped on a 

 fmall plate of porcelane, glafs, or any kind of glazed earth ; and afterwards pour fome 

 drops of water from a certain height, which on uniting together quickly flow like a fmall 

 torrent over the oil ; it will be feen, that notwithftanding the force with which this fmall 

 torrent ftrikes the drop of oil, it is not capable of difplacing it and carrying it oiF, but 

 paffes over while the oil adheres to the furface of the plate, like a varnifli, which the im- 

 petuous and continued paflage of the torrent cannot remove. It is well known that plates, 

 or other culinary utenfils, cannot be cleaned by water when foiled by oil or fat, as it has 

 not force enough to detach the oily particles from their furface, though it can produce this 

 efFeft with earth, and diflblve extraftive fubftances. 



If a fmall piece of camphor be fixed upon a plate or other veflel, and as much water be 

 added as will flightly cover the camphor, the water, as Prevoft has obferved, can never 

 attain to a level above the camphor, but forms a fmall cavity or gulph, in the figure of an 

 inverted cone, in which the fummit of the piece of camphor is always perceptible; this 

 evidently proves, according to him, that there proceeds from the odoriferous body an 

 elaftic fluid of fufficient force to repel the water that furrounds it, which according to 

 the laws of hydroftatics, ought otherwife to come in contaft with and cover the camphor. 



Cit. Venturi has likewife obferved this phenomenon ; but he conceives it to be the effisdl 

 of an oily fluid which proceeds from the camphor, and prevents the adhcfion of the water 

 with the piece of camphor, and with the columns of water that furround it. 



For my own part, after the mod accurate examination, I am of opinion, that the re- 

 treat of the water is neither attributable to the emanation of an elaftic fluid, to an odorife- 

 rous vapour, as Prevoft has fuppofed, nor to the obftacle that prevents the adhefion of 



• Loco citato, p. 207. 



F 2 water 



