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5 
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CHEMICAL SCIENCE IN AUSTRALASIA. 285. 
themselves, but in the neglect to regulate them so as to produce 
the best results. 
A crushing battery that is firmly set on good foundations, 
consisting of vertical mortar blocks, well rammed with sand, 
that has substantial mud-sills and cross-sills, and the housing 
constructed so as to resist the strains put upon it, and that is fed 
regularly with ore that has been first broken by a stone-breaker,,. 
will work rapidly without very great vibration, and should put 
from two to three tons per head per twenty-four hours through a 
No. 8 screen. 
The boxes or mortars are made of various forms, and with a 
delivery which is high or low, according to the fineness or coarse- 
ness to which the crushing is to be carried, and the arrangement 
of the screens is also varied by different makers. It is in these- 
boxes that the first amalgamation takes place, and usually a stout 
copper plate is placed in a recess at the back of the box, on which, 
when the gold is coarse. a considerable proportion is retained. It 
is, also, sometimes considered advisable to place free mercury in 
the boxes, but the practice should be deprecated, as it flours the 
mercury, and a considerable loss frequently ensues. 
Outside the screens plates of copper amalgamated with mercury 
are placed to catch the gold as it flows over the surface, and in 
many cases of late these copper plates have been replaced by 
electro plates, which avoid the constant formation of a green scum 
when the plates are new. Mercury wells are also used in many 
batteries, but they are not beneficial, because, if any sulphides are 
present in the stone, they soon form a coating on the mercury and 
destroy its utility. 
For true free milling ores this treatment is all that is necessary, 
and although machines have been introduced to replace the 
stamps there are none which have as yet been tried which can 
claim to have superseded them. Probably the best of the new 
machines is the Huntingdon mill, which has achieved a certain 
measure of success, and for small mines is undoubtedly an 
economical system of crushing. It has, however, been so 
frequently erected by men who have not had any experience in 
the plant, and worked by others who are equally ignorant in the 
matter, that there have been many failures recorded in these 
colonies against comparatively few assured successes. 
The Globe mill again claims to supersede the stamps, but has 
not yet, so far as we are aware, succeeded in establishing itself 
at any mine. Another machine, the Ashcroft Pulveriser, 
which has been patented, works upon a different system, the 
grinding being done by heavy balls and pestles, an attempt 
being made to imitate, as closely as possible, the action of 
the pestle and mortar. The inventor claims that the motion 
of a ball, or a hemispherical surface, revolving on its own axis at 
the same time as it is driven round the pan, is the most economical. 
way of reducing mineral to fine powder. 
