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Amalgam of copper. By precipitating copper on mercury 

 electroly tically, a mass of crystals is gradually formed. After 

 a certain time the crystals begin to get fringed with pink^ 

 indicating uncombined copper. In this state the amalgam is 

 found to be nearly a binary compound. On applying strong 

 pressure to an amalgam containing excess of mercury, the 

 latter is driven off, leaving a hard mass composed of equiva- 

 lents of the metals. If, however, the pressure be continued 

 for a long time, the resulting amalgam contains more than 

 one equivalent of copper, indicating a partial decomposition. 



The Author gave an account of his experiments with 

 amalgams of silver, platinum, lead, zinc, and tin. In the 

 case of the latter amalgam, long-continued pressure drives off 

 nearly the whole of the mercury, indicating in a striking 

 manner the efficacy of mechanical means to overcome feeble 

 chemical affinities. 



Dr. Angus Smith said, It is difficult to tell the exact limits 

 of chemical and mechanical action, because they flow into 

 each other. Let us call the attraction of surfaces a mechanical 

 action, as it is not to our knowledge a chemical combination. 

 Porous bodies exercise this to a very large extent, and yet do 

 not produce chemical compounds. The amount is limited on 

 one side by the pressure of the atmosphere. Chemical com- 

 pounds are too powerful to be affected by such slight forces. 

 Porous bodies or surfaces do not take up others in chemical 

 equivalents so far as we know ; the full capacity of saturation 

 is not satisfied, because of counteracting influences. Water 

 admits air very rapidly, but it is held so slightly that it is 

 affected by atmospheric pressure, and even seems to follow 

 exactly the atmospheric pressure ; but a portion is held with 

 such power that it is extremely difficult to remove, and is not 

 ever removable by the mere removal of pressure as far as we 

 know. The small affinity of the great mass or surface of 

 water is equal to a great affinity for a small amount of air. 

 All masses have more or less this mechanical action, but, as 



