1868.] 



Chemical Reactions produced by Light. 



99 



forth, and grow in a few seconds into perfect flower-like forms. The most 

 curious appearance that I noticed was that of a cloud resembling a serpent's 

 head : it grew rapidly ; a mouth was formed, and from the mouth a cord 

 of cloud resembling a tongue was rapidly discharged. The cloud of iodide of 

 isopropyl had a character of its own, and differed materially from all others 

 that I had seen. A gorgeous mauve colour was developed in the last 

 twelve inches of the tube ; the vapour of iodine was present, and it may 

 have been the sky-blue produced by the precipitated particles which, 

 mingling with the purple of the iodine, produced this splendid mauve. 

 As in all other cases here adduced, the effects were proved to be due to 

 the light ; they never occurred in darkness. 



I should like to guard myself against saying more than the facts war- 

 rant regarding the chemical effects produced by light in the following three 

 substances ; but the physical appearances are so exceedingly singular that 

 I do not hesitate to describe them. 



Hydrobromic Acid. — The aqueous solution of this acid was placed in a 

 small Woulfe's flask, and carried into the experimental tube by a current 

 of air. 



The tubebeing filled with the mixture of acid, aqueous vapour, and air, 

 the beam was sent through it, the lens at the same time being so 

 placed as to produce a cone of very intense light. Two minutes elapsed 

 before anything was visible ; but at the end of this time a faint bluish cloud 

 appeared to hang itself on the most concentrated portion of the beam. 



Soon afterwards a second cloud was formed five inches further down the 

 experimental tube. Both clouds were united by a slender cord of cloud of 

 the same bluish tint as themselves. 



As the action of the light continued, the first cloud gradually resolved 

 itself into a series of parallel disks of exquisite delicacy ; the disks rotated 

 round an axis perpendicular to their surfaces, and finally they blended to- 

 gether to produce a screw surface with an inclined generatrix. This surface 

 gradually changed into a filmy funnel, from the end of which the "cord " 

 extended to the cloud in advance. This also underwent modification. It 

 resolved itself into a series of strata resembling those of the electric dis- 

 charge. After a little time, and through changes which it was difficult to 

 follow, both clouds presented the appearance of a series of concentric fun- 

 nels set one within the other, the interior ones being seen through the spec- 

 tral walls of the outer ones ; those of the distant cloud resembled claret- 

 glasses in shape. As many as six funnels were thus concentrically set 

 together, the two series being united by the delicate cord of cloud already 

 referred to. Other cords and slender tubes were afterwards formed, and 

 they coiled themselves in spirals around and along the funnels. 



Rendering the light along the connecting-cord more intense, it diminished 

 in thickness and became whiter ; this was a consequence of the enlar^e- 



h 2 



