CHEMICAL SCIENCE. 205 



merely to carbonic acid; that all the water of large towns contains 

 organic matter ; that water purifies itself from organic matter in 

 various ways, but principally by converting into nitrates; that water 

 can never stand long with advantage, unless on a large scale, and 

 should be used when collected, or as soon as filtered. 







DURABILITY" OF ICE. 



" SIR FRANCIS HEAD, in his ' Emigrant,' has attributed the dura- 

 bility of the Wenham Lake ice, or its power of resisting liquefaction, 

 to the intense cold of a North American winter. It is perfectly true 

 that this ice does not melt so fast as English ice, but the cause of 

 this phenomenon is, I believe, very different from that assigned for it 

 by the late Governor of Upper Canada. There can be no doubt, that 

 where an intense frost gives rise to a great thickness of ice, permit- 

 ting large cubic masses to be obtained after the superficial and porous 

 ice has been planed off, a great advantage is afforded to the Ameri- 

 can ice-merchant, and the low temperature acquired by the mass must 

 prevent it from melting so readily when the hot season comes on, 

 since it has first to be warmed up to 32 Fahr., before it can begin 

 to melt. Nevertheless, each fragment of ice, when removed from the 

 store-house, very soon acquires the temperature of 32 Fahr., and 

 yet when a lump of Wenham ice has been brought to England, it 

 does not melt by any means so readily as a similar lump of common 

 English ice. Mr. Faraday tells me that Wenham Lake ice is ex- 

 ceedingly pure, being both free from air-bubbles and from salts. The 

 presence of the first makes it extremely difficult to succeed in making 

 a lens of English ice, which will concentrate the solar rays and read- 

 ily fire gunpowder, whereas nothing is easier than to perform this 

 singular feat of igniting a combustible body by the aid of a frozen 

 mass, if Wenham ice be employed. The absence of salts conduces 

 greatly to the permanence of the ice, for where water is so frozen 

 that the salts expelled are still contained in air-cavities and cracks, or 

 form thin films between the layers of ice, these entangled salts cause 

 the ice to melt at a lower temperature than 32, and the liquefied por- 

 tions give rise to streams and currents within the body of the ice, 

 which rapidly carry heat to the interior. The mass then goes on 

 thawing within as well as without, and at temperatures below 32 ; 

 whereas pure and compact Wenham Lake ice can only thaw at 32, 

 and only on the outside of the mass." LyeWs Second Visit to the 

 United States. 



OX THE FREEZING OF ALCOHOL. 



IN a recent lecture at Sorbonne, M. Despretz attempted the conge- 

 lation of alcohol, and to effect this he plunged into liquid protoxide of 

 nitrogen a thin glass tube containing a small quantity of alcohol. 

 The whole was suspended in a small vessel, at the bottom of which 

 was placed a paste, composed of solidified carbonic acid and ether, the 

 concave cover of the vessel being also filled with the same 'paste. 



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