74. The Naturalist in Nicaragua 
is lifted by cams, and let fall seventy times per minute. The 
stamped ore, in the form of fine sand, is carried by a stream 
of water over inclined copper plates covered with mercury, 
with which is mixed a little metallic sodium. Nearly the 
whole of the free gold is caught by the mercury, for which it 
has a great affinity, and accumulates as amalgam on the 
copper plates, from which it is cleaned off every twelve 
hours. The sand and water then pass over inclined tables 
covered with blankets, the fibres of which intercept particles 
of gold and mercury that have escaped from the first process, 
and afterwards into a concentrating box, where the coarsest 
grains of sand and the sulphurets of iron, copper, and silver 
are caught, and with the sand from the blankets re-treated 
in arrastres. These arrastres are round troughs, twelve feet 
in diameter, paved with stones. Four large stones of quartz 
are dragged round and round in this trough, and grind the 
coarse sand to fine powder. The gold liberated sinks into 
the crevices in the stone pavement, a little mercury being 
put into the trough to form it into amalgam. The arrastres 
and all the amalgamating apparatus is cleaned up once a 
month. The amalgam obtained is squeezed through thin 
dressed skins, and is then of the consistence of stiff putty, 
and of a silver colour. These balls of amalgam are placed 
in iron retorts, and the mercury driven off by heat and con- 
densed again in water. The balls of gold so obtained are 
then melted into bars weighing about one hundred ounces 
each, and in that state sent to England. At Santo Domingo 
about two thousand tons of ore are treated monthly, and the 
whole cost of treatment, including all charges for mining, 
carriage, reduction, amalgamation, and management, is only 
about eight shillings per ton. The loss of mercury is about 
twenty pounds for every thousand tons of ore treated; the 
smallness of the loss in comparison with that of many other 
gold-extracting establishments being greatly due to the 
employment of sodium in the amalgamating processes. The 
loss of mercury usually occurring in amalgamation work is 
principally caused by its mineralisation, and sodium has such 
an intense affinity for oxygen and sulphur, that it reduces 
the mercury to its metallic form again, and prevents its 
being carried off in light mineralised flakes and powder. 
The band of auriferous quartz veins worked at Santo 
