MOTIONS OF ODOROUS SUBSTANCES. 53 



of tin upon water, and bring the extremity of a glafs lube 

 wetted with ether within fome centimetres diftance of it, the 

 plate recedes. 



Small pieces of camphor, thrown upon mercury that had Camphor upon 

 been well dried, were agitated there with the fame motions as r ? mercury, 

 on the water. In order that this experiment may fucceed, it 

 is neceffary that the mercury mould be well cleaned or dried : 

 the fmalleft particle of oil or fat fpread upon its furface flops 

 the motion. The pieces of camphor ought to be very fmall, 

 the reafon of which will be feen hereafter. 



Very thin plates of mica, placed upon mercury, and charged Camphor upon 

 with a fmall piece of camphor, move in the fame manner as ™" u °* Ung on • 

 upon water. 



The benzoic acid likewife aflumes a rotatory motion upon Benzoic acid, 

 mercury ; but it is neceflary that it be reduced into almoft im- 

 perceptible fragments. An oily aureola forms itfelf round thefe 

 fragments. Nothing fimilar to this is obferved round cam- 

 phor, not even when examined with the microfcope. The 

 metallic Iuftre of the mercury is not impaired by it. 



It refults from thefe fa&s, that the prefence of water is not Water umiecef- 

 neceftary to the motions of odorous fubftances. fary * 



Thefe fubftances caufe the water to recede upon plates of 

 alum, of pottery [terre a fa'iance], and of gum arabic, in the 

 fame maimer as upon a wet plate of porcelain. This retreat 

 is not therefore owing to the elective attraction of the oily or 

 odorous fubftance for the furface of the plate. 



Finally, notwithftanding the aflfertion of Dr. Carradori, 

 camphor moves in very confined vefTels : Citizen Prevoft has- 

 feen it agitated in capillary tubes, into which it was intro- 

 duced in very minute fragments. 



From thefe fafts Citizen Prevoft concludes, that the inter- Inference, that 

 vention of an elaftic fluid is neceflary to the produaion of thefe^^ ^ 11 ^ 

 phenomena. To the facls which he has adduced, I fhall fub- elaftic fluid, 

 join the following, which appear to me to decide the queftion 

 relative to the motions of camphor upon water. 



If we cut a fmall piece of camphor, of the weight of a few Experhntr.tum 

 grains, into the form of a cone, and approach it to the diftance cruc:u 

 of four or five millemetres of a very fmall piece of leaf gold 

 floating upon the furface of the water, prefenting the point to 

 it, this fmall piece of gold is repelled ; and we may thus con- 

 4u6l it through the whole extent of the vafe, without ever 



being 



