Skey. — On the Movements of CampJwr on Water. 479 



First tlien in regaxd to the nature of this modification. Camphor, I 

 should remind you, has properties affecting this question as follows : — It is 

 soluble in water, and so without doubt combines with it ; it is not decom- 

 posed by water, even in conjunction with an that is at common temperatm-es, 

 and it is a resin slowly volatile at such temperatures. 



Now camphor, as we have seen, modifies a very much larger extent of 

 surface when placed in contact with water than when suspended over it. 

 "We may, therefore, be certain that the modification in question is not 

 occasioned simply by a deposit of condensed camphor vapour upon the 

 water surface, but rather by some combination of it with water. This 

 combination, however, is not that which is obtained by saturating water 

 with camphor in the ordinary way (a compound containing one part of 

 camphor to one thousand parts of water), as is shown by the fact I have 

 already stated to you, that a saturated solution of camphor in water allows 

 camphor to describe movements upon its surface ; this compound, therefore, 

 is one new to us, it can only exist as a thin surface film, and is therefore 

 doubtless one far richer in camphor than that which we already know of, 

 a compound indeed so highly camphoretted that it, in all probability, 

 partakes in an eminent degree of the characters of an oil.''' However, it is 

 impossible for me as yet to obtain dnect evidence as to the nature of a film 

 so exceedingly thin as this. We must therefore for the present rest content 

 with the indirect evidence which we now have. 



Granted, then, that the modification effected upon a surface of water by 

 camphor is owing to a combination of the two for the production of a highly 

 camphoretted oil, I have only now to show the precise manner in which 

 this compound induces camphor to move. 



For this purpose I will refer you to the effect which a drop of oil has 

 when placed upon water laden with an indicatory substance, such as clay 

 in fine particles ; the oil spreads quickly and regularly around, and in the 

 act urges the clay to the side of the containing vessel, where it becomes 

 stationary. Now the clay and the oil here are, I hold, fairly representative 

 of the camphor and its oily compound ; there is this difference, however, in 

 the movement of the oils, and it is an important one, it is a difference upon 

 which all camphor movement depends, — the spread of oil in the case of 

 camphor is not even around it, as is that of the other oil ; were it so there 

 would be no such phenomenon as that we are investigating. Eegularity of 

 spread is in this case impossible, because the production is kregular, owing 

 to the highly crystalhne nature of camphor, and its great fragihty, whereby 



* I have lately observed that water thus modified, when compared side by side 

 with pure water, exhibits a higher lustre than the pure water does, a fact greatly in 

 favour of tliis view. 



