1850.] On Ice and Freezing Water. 373 



into this country under the name of the Wenham Lake ice 

 (though it is chiefly supplied from Norway) may be regarded 

 as one of the purest natural substances. Mr. Faraday first 

 showed how entirely colouring matter, salts and alkalies are 

 expelled in freezing*. A solution of sulphate of indigo, diluted 

 sulphuric acid, and diluted ammonia were partially frozen in 

 glass test-tubes : as soon as the operation had been carried on 

 long enough to produce an icy lining of each tube, the unfrozen 

 liquid was poured out and the ice dislodged. This ice was 

 found in every instance perfectly colourless, and, when dissolved, 

 perfectly free from acid or alkali, although the unfrozen liquid 

 exhibited in the first experiment a more intense blue colour, in 

 the second a stronger acid, and in the third a more powerful 

 alkaline reaction than the liquor which was put into the freezing 

 mixture. Mr. Faraday also devised a method for making this 

 ice perfectly clear and transparent as well as colourless. By 

 continually stirring the liquid, while freezing, with a feather, he 

 brushed away globules of air as fast as they were dislodged 

 from the freezing fluid, and thus prevented their becoming 

 imbedded in the ice. Having noticed the rapidity with which 

 water absorbs air as soon as it is thawed, Mr. Faraday called 

 attention to the importance of this natural arrangement to 

 aquatic plants and animals, to whose life air is as indispensable 

 as to those which live on land. Mr. Faraday then referred to 

 Mr. Donny's discovery, that water, when deprived of air, does 

 not boil till it reaches the temperature of 270, and that at that 

 degree of heat it explodes. He mentioned that he suggested 

 to Mr. Donny that ice when placed in oil (so as to prevent its 

 receiving any air from the atmosphere on thawing) would pro- 

 bably explode on reaching a sufficient temperature. This 

 experiment had been successfully tried by Mr. Donny, and was 

 as successfully repeated on this occasion. Mr. Faraday then 

 invited attention to the extraordinary property of ice in solidi- 

 fying water which is in contact with it. Two pieces of moist 

 ice will consolidate into one. Hence the property of damp 

 snow to become compacted into a snowball an effect which 

 cannot be produced on dry, hard-frozen snow. Mr. Faraday 

 suggested, and illustrated by a diagram, that a film of water 

 must possess the property of freezing when placed between two 

 * See ice from solution of chlorine, p. 82. 



