406 Transactio'ns. — Chem istry. 



sary as a property of the substance floating thereon ; for it seems to be 

 certain that all the substances here cited which describe movements upon 

 water, with the exception of camphor, form solutions or compounds with 

 water possessing more viscidity than water does. As regards camphor, we 

 can get no positive evidence that the substance it forms upon water is thus 

 more viscid than water, as we cannot collect it in sufficient quantities for 

 the examination necessary ; but we may safely assume, from analogy, that 

 it is viscid, and highly so. I think it may be taken as a fact that any sohd, 

 which, when placed upon water, has a greater tendency to spread upon its 

 surface than to combine with the bulk of it (as camphor, citric acid, etc., do), 

 will form a compound therewith of a natm^e more viscous than water. 

 I suppose the solution thus radiating from a sohd along the water surface 

 to be saturated, as in such a condition its viscosity will be greatest. I need 

 not demonstrate to you that a substance which forms with water a com- 

 pound more viscid than water, should spread largely when placed in contact 

 with the sm-face of water ; it is a mere physical matter, one of least re- 

 sistance ; such substances encounter but little more than haK the resistance 

 to movement when extending along the sui-face than when penetrating the 

 liquid underneath ; the movement in the former case is, too, far more rapid 

 than that in the latter ; but as capillary attraction is probably concerned as 

 an accelerator of such movement, I cannot well claim that this superior 

 rapidity is a measure of the greater ease with which the viscid product ex- 

 tends itself over the sm-face than it does internally. 



And now with special regard to the cause of camphor movement : it will 

 occur to you that if the compound which camphor forms with water is so 

 highly viscid as I here maintain, the movements in question may have their 

 stimuli m part due to an effect springing out of this viscidity ; it would seem 

 that, — as there is a constant production of this viscid substance close to 

 the camphor, and a little above the water-line, as well as on it, — this sub- 

 stance exercises a slight pressure on the camphor in virtue of its viscidity, 

 and the camphor, therefore, is urged wherever the solution is less viscid. I 

 conceive this supposition to be a correct one, and, therefore, that in addition 

 to the motive power capable of being derived fi'om the effect of superficial 

 affinities and adhesions, as cited in my former paper upon this subject, there 

 is that derivable from an unequal solution of the substance operated with 

 in a menstruum of unequal viscosity. 



