QAP, ANNUAL REPORT 
A Simple Algebraic Method.—After once the best proportion of a 
mixture has been established, the daily mixture can be calculated from 
the raw materials available by a simple calculation depending on the 
lime content of the two materials. 
Let x=weight of limestone in charge, 
y=weight of clay in charge, 
a=per cent. of calcium oxide in the limestone, 
b=per cent. of calcium oxide in the clay, 
C=per cent. of calcium oxide in the mixture, 
ax--by x c—b 
then c=— = 
Off <(A—@ )\ =v (C—D)) Of —==——— 
x+y y ac 
Experimental Apparatus for Cement Burning. —Preliminary burn- 
ing tests are made by weighing out the ingredients, grinding them 
to a powder in a _ ball-mill, moistening the dust and making 
into small balls or cubes and burning them in a test kiln. The writer 
employed for grinding his mixture the iron ball-mill already mentioned, 
which has the shape of a flattened sphere, 24 inches in -diameter 
and 77% inches wide at the center, making 27 revolutions per 
minute. The mill is made of chilled iron, and provided with a cap whose 
surface, as well as the surface of the mill opening, are ground, forming 
a tight joint. With 126 pounds of flint pebbles, 30 to 40 pounds of 
mixture can be ground sufficiently fine in from three to five hours. ‘This 
mill is shown in Fig 29. 
For the burning the writer employed a crucible furnace, lined with a 
mixture of go parts of burnt magnesite and Io parts of Portland cement, 
with an inside diameter of 4 inches and a height of 6 inches, fired with 
gasoline gas, and using air under a pressure of about 18 pounds to the 
square inch, furnished by a Westinghouse locomotive air pump. This 
was quite satisfactory for smaller quantities; after once heated, a highly 
calcareous cement could be burnt in 20 minutes. The furnace space 
was simply filled with the balls of the raw mixture which were, of course, 
perfectly dry. 
For larger quantities of cement requiring a high temperature a 
furnace shown by figure 30 on page 245 was used which consisted 
essentially of a straight shaft of fire-brick, with 4 inch walls, and divided 
into three distinct divisions. Into a space 4 inches high at the bottom, 
air was forced under a pressure of about 12 ounces, from a 
blower through a 2 inch pipe. This space was divided from the next 
division by means of a cast iron plate provided with concentric rows of 
holes. Above this plate, about 5 inches away from it, an iron pan was 
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