478 Transactions, — Chemistry, 



movement, it occurred to me to try camphor itself. I placed a large piece of 

 it upon water in a vessel closed from tlie air, and found, after the lapse of 

 about four hours, that it was stationary, and that fresh pieces put therein 

 would not move. I then took out the camphor and exposed the water 

 freely to the air for a short time, when I found that camphor would then 

 describe very lively movements upon it. The same kind of effects are not 

 produced if the camphor is kept wholly immersed in the water, not even if 

 the time of contact is prolonged to a week. I further found that a water^ 

 surface, which has been rendered unfavourable for these movements by 

 camphor, is also in a very unfavourable condition for the spread of oils 

 thereon, so much so that some of them, when so placed, that is, of course, 

 when used in small quantity, keep nearly to the drop form. 



The very pertinent facts are, then, now distinctly shown, that many 

 vapours are obstructive to camphoric movements when condensed within or 

 upon the upper stratum of any water on which camphor is moving, and 

 that among these substances is camphor itself. Now we have already seen 

 that all the substances just named above (and this includes camjyhor) are 

 capable under certain circumstances of giving very decided and rapid move- 

 ments to solid particles when they occupy a water-surface ; and we have 

 also seen that these vapours do not effect this directly by what I may here 

 designate vaj)our force, but rather by surface modification. The conclusion, 

 therefore, which one is led to by a consideration of all this is, that the 

 movements of camphor in question are the effect of surface modification and 

 modiflcatiun ivJiich it -produces itself. 



The analogy is, I hold, complete between resin upon water moving away 

 from that which has been modified by vapour, and camphor upon water 

 moving away from the water it has modified, except that we have one sub- 

 stance less in the latter than in the former case — thus, camphor placed 

 upon water gives up a part of its substance to the upper stratum thereof; 

 this part represents the vapours, whether of alcohol, ether, or camphor, 

 which are resident in the clearing they have made amongst the particles of 

 resin with which the water has been laden ; the remaining part of the 

 camphor represents the resin which has been removed to make this clearing. 



Such is the theory which I submit to you as explanatory of the pheno- 

 mena we have been observing. I think you will readily allow that it is at all 

 events the most probable of any which you have now had for this purpose, 

 and now it only remains for me to state to you what I conceive to be — 



1. The precise nature of the surface modification which I have 



credited camphor with producing. 



2. The manner in which a surface so modified forces camphor to 



move. 



