84 NEW YORK STATE MUSEUM 



cylinder set on a slight incline and turned slowly on roller bearings 

 by means of a large spur wheel at the upper end. The rock enters 

 the cylinder at the same end and gradually works its way down as 

 the cylinder revolves, being lifted and dropped by blades attached 

 to the sides. The hot gases from the furnace are forced by a fan 

 into the brick chamber surrounding the cylinder where they are 

 mixed with sufficient air, admitted through the registers at the base, 

 to give the desired temperature. From the conmingling chamber 

 the air and furnace gases are drawn by a fan through hoods into 

 the interior of the cylinder which they traverse in a direction oppo- 

 site to that taken by the material. The temperature of the interior 

 is maintained between 400° and 600° F., accoirding to the character 

 of the rock and the desired product. i\s the rock remains in the 

 cylinder only 10 minutes, there is little danger of overheating inci- 

 dent to the kettle method. A thermometer is placed in the discharge 

 spout where the operator can watch it and regulate the flow of 

 gases so as to give a uniformly heated product. 



An indispensable feature of the Cummer process is the calcining 

 bins into which the steaming material from the kiln is removed. 

 Four bins are required foir each cylinder. They are made of brick 

 and lined with paving brick which have little absorbing power. The 

 material remains in the bin for about 36 hours, during which time 

 the free moisture not driven ofl: in the cylinder is removed as well 

 as a further part of the water of crystallization. While the cal- 

 cination is going on in the bin, outside air is excluded, thu's allow- 

 ing the heat of the material to equalize itself throughout the mass. 

 Small variations in temperature during the day's run of the cylin- 

 der have little or no influence on the character of the product so 

 long as the average remains fairly constant. With the use of four 

 bins the process is absolutely continuous ; while one is being filled, 

 calcination is going on in the second and third, while the fourth is 

 being emptied. 



The arrangement of a mill in which the Cummer process is used 

 is shown in figure 9. The kiln is installed in the plant of the Ly- 

 coming Calcining Co. at Garbutt, which has a capacity of 50 tons 

 of plaster in 11 hours. The fuel is soft coal. According to the 

 manufacturers' circular the consumption of fuel, when a good 

 grade of coal is used, averages about 70 pounds for each ton of 

 calcined material, exclusive of that employed for driving the plant, 

 which is a relatively small item. 



Another continuous process is described by F. A. Wilder^ as in 



* Iowa Geol. Sur. 1902. 12:213. 



