364 CEMENT MATERIALS AND INDUSTRY. [bull. 24| 
is possible to economically reduce the percentage of moisture in the 
dried product to about one-fourth of 1 per cent. 
The temperature to which the product is carried in drying is not a 
matter of serious moment so long as it does not pass the point at which 
the slag begins to recrystallize. Theoretically, of course it is unneces- 
sary to carry the temperature above 212° F., but in practice it is 
economically impossible to keep it as low as this. It may be carried 
as high as a dull-red heat without injury to the slag. Indeed, it is 
probable that drying at relatively high temperatures improves rather 
than impairs the hydraulic properties of the slag, as it is well known < 
that the natural pozzuolanas are improved by roasting. It would not, 
therefore, be a matter of surprise if drying the slag at a higher tem- 
perature than is actually necessary should result in materially acceler- 
ating the set of the resulting cement, and also in increasing the strength, 
of briquettes made from it. 
The Ruggles-Coles dryer consists of two concentric hollow cylin- 
ders bolted together and revolving on an axis slightly inclined from; 
the horizontal. The outer cylinder is made of steel plates, the longi- 
tudinal seams having butt joints with inside lapping straps. The 1 
inner cylinder, which is also made of steel, is connected with the 
outer cylinder at the center by heavy cast-iron arms solidty riveted to 
both cylinders, and at each end by two sets of adjustable or swingings 
arms, which prevent expansion and contraction from affecting the» 
rivets or joints. At the head or upper end the inner cylinder projects* 
beyond the outer cylinder, passing into a stationary head or ami 
chamber to the hot-air flue of the furnace with which it is connected. 
At the lower or discharge end is another stationary head, forming an 
air chamber, through an opening in the bottom of which the dried 
material is discharged. This head is provided with a damper to regu- 
late the temperature. 
The outer cylinder is set at an inclination of about 0.375 inch tc 
the foot. It is secured to two heavy rolled-steel bearing rings which 
rest and revolve upon eight bearing wheels supported by oscillating 
arms or rockers. The lateral motion of the cylinder is taken up by 
four thrust wheels. The d^er is revolved by a cast gear secured to 
the outer cylinder, and this is driven by a shaft and pinion extended 
beyond the end of the machine and supported in two babbitted jour 
nal boxes fitted to the frame. The entire machine is fitted and secured 
to a heavy frame of 8-inch I beams braced and framed together anc 
usually set on a concrete foundation. The exhaust fan is placec 
where most convenient to drive and is connected with the outer cylin 
der try suitable flue. The furnace is built independent of the machine 
and connected with the head end of the inner cylinder by an iron flue 
built with fire brick. A specially designed burner is substituted foil 
the furnace for the use of oil, gas, or powdered coal. 
