Green Ice. < 51 



GEEEIST ICE. 



BY HENRY J. SLACK, F.G.S., 

 Member of the Microscopical Society of London. 



It is sometimes worth, while to remark upon a subject that may 

 appear common-place, and I am induced to say a few words 

 upon the often-noticed phenomenon of ice being coloured 

 green by its enclosing confervoid vegetation, simply upon the 

 ground that as it has lately interested me, it may interest other 

 constant readers of the Intellectual Observer. During the 

 severe frost of January, I was walking, on a clear sunny day, 

 in company with a friend, when our attention was drawn to 

 the brilliant green tint of sundry masses of ice scattered over 

 the frozen surface and about the margin of a pond, on the 

 Lower Heath, Hampstead, near the queer looking edifice dedi- 

 cated to the water gods of the place. A man was amusing 

 himself with a pickaxe breaking up the ice near one end of the 

 pond, and scattering the fragments about him. Some he sent 

 whizzing along the frozen water, and its surface was soon 

 variegated by masses that gleamed with a beautiful beryl tint. 

 Taking up some of these pieces I was struck with the small 

 quantity of green matter that sufficed to tinge a considerable 

 block, and as the cold was intense, I put a fragment in the 

 pocket of a large great coat, just wrapped in a piece of paper, 

 and thus carried it home nearly dry. Placed in a white por- 

 celain vessel in my study it soon thawed, and at the bottom of 

 the water was a little green stuff, which microscopic examination 

 showed to consist of a minute oscillatoria, and some other 

 conferva of which I don't know the name. These little plants 

 seemed quite alive, as a high power detected no sign of decay 

 in their bluish green chlorophyll ; but their life processes must 

 have been comparatively quiescent, as they remained for some 

 days at the bottom of the vessel. Had they been active I pre- 

 sume they would have evolved enough air-bubbles to have 

 caused them to float. A few days afterwards I went for a fresh 

 supply, and found every piece of ice I examined very irregular 

 in structure, and full of cavities I took for air-bubbles. A 

 pocket lens showed the parallel planes of freezing very prettily, 

 but did not detect any cavities round the conferva, which 

 was disposed in minute tufts — not at all close together. I did 

 not in any case see any conferva in an air-bubble, or any dis- 

 tinct air bubble attached to a conferva. Some masses of ice of 

 an intense beryl green were broken with a hammer, and it 

 was curious to remark how very small a quantity of the vege- 

 table matter, distributed as I have described, tinged the whole 



