1G4 
Amalgam of copper. By precipitating copper on mercury 
electrolytically, 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 witlx 
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 he 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 ; hut a portion is held Avith 
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 
