Polytechnic Association. 909 



nomeuon : 1. Light may decompose the chlorine molecule into 

 atoms. 2. The more refrangible rays of light may effect some 

 unknown change, which results in heat and causes expansion. 3. It 

 may be assumed that there are bodies which increase in temperature 

 more under exposure to the violet than to the red rays. The author, 

 regarding the first view as the most probable, believes the expansion 

 of chlorine is the effect of a temporary separation of atoms under 

 the influence of the more refrangible rays. 



Prof. P. H. Tan der Weyde — The first explanation, I think, is the 

 most probable. It may be that light has the same effect upon substances 

 as ozone. If that is the case, the volume must increase: Ozone is 

 heavier than oxygen; for three atoms of ozone have the same volume 

 as two atoms of oxygen. If we could split up all the chlorine into 

 single atoms it would double its volume. 



The President — The greatest expanding power of the spectrum is 

 the red ray, and as these substances expand most in the violet ray, the 

 only explanation is that the effect is produced by actual chemical 

 decomposition. 



Prof. Yan der Weyde — Hydrogen and chlorine, when exposed to 

 the actinic ray, will suddenly combine. When chlorine alone is 

 exposed to the actinic ray it will partially combine with hydrogen, 

 and on this fact Bunsen has formed an actinomoter. If the actinic 

 ray decomposes chlorine into single atoms, it predisposes it to combi- 

 nation with hydrogen, for which the single atom is required. There 

 seems to be intimate relation between this discovery and that known 

 fact. 



Skeleton Leaves. 

 Mr. J. F. Kobinson describes, in Hardwick's Science Gossip, a 

 simple method of preparing skeleton leaves, which seems preferable 

 to the old and tedious method of maceration, and which he recom- 

 mends to all young botanists, especially to his fair friends, who take 

 up the science of botany more as an intelligent amusement than for 

 severe study. First dissolve four ounces of common washing soda in 

 a quart of boiling water, then add two ounces of slaked quicklime, 

 and boil for about fifteen minutes. Allow the solution to cool ; after 

 ward pour off all the clear liquor into a clean saucepan. When this 

 liquor is at its boiling heat, place the leaves carefully in the pan, and 

 boil the whole together for an hour, adding from time to time enough 

 water to make up for the loss by evaporation. The epidermis and 

 parenchyma of some leaves will more readily separate than others 



