STATE GEOLOGIST. 225 
requires 30 per cent. less power under similar conditions to do the same 
amount of work which can be done by the other form of machine—the jaw 
crusher. It is also claimed that, because of the concave stationary surface 
and the impact of the revolving cone at the unsupported center of the 
masses of stone, a more perfect cubiform product is obtained. 
Naturally it requires more power to break stone to one-half inch size 
than it does to break it to two and one-half inch size. This must be 
taken into account in ordering machines. The manufacturers of this 
machine claim that “The Gates’ breaker will not require over one horse 
power per ton of rock broken per hour,” for the hardest stone broken so 
as to pass a 2% inch ring. 
Figure 126 shows a section of the Austin portable crusher, which is 
a very simple machine of a similar type. 
Figures 127 and 128 show view and section of the Farrel crusher, 
a very substantial compact machine of the jaw crushing type. 
SCREENS. 
Figure 129 illustrates revolving screens. The perforated screen 
sheets are easily removed and replaced when worn out, or they can be 
changed quickly when other sizes of stone are required. 
Cheaper gravity screens can be used, but they are not quite so efficient 
in screening. They are of perforated sheet metal, as the revolving screens, 
but are in flat sheets and attached in the bottom of inclined chutes down 
which the crushed stone is allowed to slide dropping through the holes 
in the various sections as the size of aperture admits. 
CONCRETE MIXERS, 
There are numerous forms of concrete mixers, and many makers of 
the same form. At first engineers were averse to accepting machine 
-~mixed concrete, fearing inferior mixing, improper proportions of water 
and various other troubles. Now a large majority of engineers prefer 
machine mixed concrete, electing, however, to choose the form of mixer 
which shall be used. 
The Drum Mixer.—The Ransome patents cover a drum mixer, a 
cylindrical machine having openings at either end and resting upon fric- 
tion rollers. It is driven by cog wheels. working in a cogged rim to the 
drum and the whole driven by steam, air, or electricity. 
Inside this drum are kneading wings for mixing, and hinged shelves 
by which the concrete is lifted and thrown into a chute. These shelves 
are set for mixing or discharging by the movement of a single lever 
without stopping the machine. Figures 130 and 131 show the receiving 
and discharging ends of the machine respectively. 
15—S. G. 
