gS. , On the Motions of Camphor and Odorant Bodies, 



perficles to the air, evaporates more fpeedlly, and as Its evaporation is In proportion to Its 

 extent upon the water, the reafon is evident why the camphor is fo fpeedily confumed, and 

 why by this rapid confumption the particles are induced to change their figure. 



It is true that the oil camphor, which is extended over the water, gradually evaporates 

 or entirely volatilifes. Of this I have been clearly convinced by the following experiment : 

 after two pieces of camphor which had -been in motion on the furface of water in a glafs 

 were confumed, I expofed the glafs to the air, that the oily film of oil camphor which 

 covered the furface might evaporate i four hours afterwards I put in other pieces, but did 

 not obferve the accuflomed winding motions ; I foon removed them, and at the expiration 

 of four hours I again threw in frefli pieces ; and the motions took place as ufual. Hence 

 it appears, that after four hours the oil of the camphor had not totally evaporated, though 

 in eight hours it had difappeared, and the water remained perfedily clear. 



Venturi, however, was well acquainted with the attra£tion that exifts between oil and 

 the furface of water ; fince he obferves that a drop of oil, if it had no _affinity with the 

 furface of vBatcr, would remain upon it without extending ; it may therefore be faid, that 

 an attraftion exifts between the fubftance of oil and the furface of water. 

 - The experiments made by Venturi with fmall columns or fticks of camphor, plunged 

 half their height perpendicularly in water, and cut horizontally at the level of that fluid, 

 in the fpace of twenty-four hours, only proves that the greateft folution of camphor is 

 cfFe£led exaftly where it touches the furface of the water; and confequently they tend to 

 confirm my conclufion, that camphor contains an oil which expands over the furface of 

 water in confequence of an attra£lion between it and this furface ; and that it is by fuch 

 extenCon that it more fpeedily evaporates. There is not, as he imagined, a greater a£ti- 

 vity exerted upon the camphor at the points where the air and water meet in contadt 

 with this fubftance, but only where the camphor touches the furface of the water. Air 

 only conduces to this influence upon the phenomena, in proportion as it favours the eva- 

 poration of the oil of camphor which is extended over the furface of the water. I am 

 well convinced that air here has no influence, and that the whole efFe£t ought to be attri- 

 buted to the union of the furface of the water. 



But it appears that Venturi has at length difcovered his error, fince he fays, he obferved 

 that the folution of camphor at the furface of water takes place the quicker the more that 

 furface is extended. For in fmall veflels the cutting of the columns is not fo quickly 

 effeded. 



Prevoft has alfo confirmed the attradlon of the furface of water ; as he obferved that 

 camphor when in a humid air, or fubmerfed in water, does not undergo fo much lofs or 

 confumption, as it fufi^ers when it immediately touches the water ; but he attributes this 

 to the water, which favours the evolution of the odoriferous fluid. 



The rapid motion of odoriferous bodies upon water, and particularly that of camphor, 

 is prevented after fome time, as Cit. Prevoft has obferved, in confequence of the attraftion 

 of the furface of the water for the oil which expands being dlmlniflied : neverthelefs, the 

 fmall pieces of camphor which colle£l on the water after their revolving motion has ceafed, 



always 



