Camphor towards the Light. 359 



may generally be seen attached to the sides the nearest to the 

 light. Many other substances which are capable of the same 

 kind of sublimation exhibit the same phenomena in their solidi- 

 fication. 



" M. Chaptal first made the observation that when a number 

 of capillary crystals shoot up the sides of a glass vessel contain- 

 ing a saline solution, they attach themselves only to that side of 

 the vessel which is most strongly illuminated. He w 7 as thus 

 able to cause crystals to form on any selected side ; and by 

 placing a screen before the vessel, he found that the fine between 

 light and darkness was distinctly marked by the limit of crystal- 

 lization. This result is most readily obtained with the metallic 

 salts." 



Professor Brande, in his 'Manual of Chemistry' (1848, p. 11), 

 has a similar statement, and our latest printed authority, Pro- 

 fessor Miller's ' Elements of Chemistry 3 (vol. iii. 2nd edit., 

 1862), states (p. 540) that camphor " becomes slowly volatilized 

 at common temperatures ; and if kept in glass bottles, is gradu- 

 ally sublimed and condensed in octahedral crystals on the side of 

 the vessel which is exposed to the light." 



The motion of camphor towards the light was investigated by 

 Dr. Draper, Professor of Chemistry in New York, who, in the 

 Appendix to a work published in 1844, entitled " Treatise on 

 the Forces which produce the organization of Plants," brings 

 together the results of his experiments on the camphor-motions 

 which had been previously published in scientific journals. 



It did not escape the notice of the early observers that other 

 substances besides camphor moved towards the light in the 

 glass vessels that contained them. Thus M. Dorthes, one of 

 ChaptaPs laboratory pupils, states that spirits of wine, water, 

 &c, "always condense on the most illuminated sides of the 

 vessels." Dr. Draper found that if iodine be heated in a glass 

 vessel and be placed in the sun, the vapour would in like manner 

 condense on the most illuminated side. His method of opera- 

 ting with camphor was to place it in a vessel, which was then 

 exhausted of air, and so moved into the sun. A crystalline 

 deposit w r ould be made on the sunny side in about five minutes, 

 and this w r ould increase during the next two hours, and some- 

 times cover the whole side of the glass. If a ring of tinfoil 1^ 

 inch internal diameter and -J an inch wide were attached to the 

 glass, it prevented the deposit in and about it, and would even 

 remove a deposit already formed. A similar effect was produced 

 if the ring were placed near the glass instead of being in contact 

 with it. 



Dr. Draper states^ further, that the camphor-vessel may be 

 kept in the dark for any length of time without producing a 



