362 CEMENT MATERIALS AND INDUSTRY. [bull. 243. 
to obtain. These points, of course, should be settled in advance of 
the erection of the cement plant. 
In the case of any given furnace running on ores and fluxes which 
are fairly steady in composition and proportions, the selection of the 
slag used for cement making may often be largely based on its color, 
checked by determinations of lime. The darker-colored slags are 
generally richest in lime, except when the depth of color is due to the 
presence of iron; the lighter-colored slags are usually higher in silica i 
and alumina. Candlot states further a in this connection that the slag.: 
issuing at the commencement and toward the end of a discharge should I 
be rejected because of the chilling which attends its slow movement. 
GRANULATING THE SLAG. 
Assuming that a slag of proper composition has been selected, the* 
first step in the actual manufacture of slag cement will be the " gran- 
ulation" of the molten slag. Granulation is produced by bringing: 
molten slag into, contact with a sufficient amount of cold water. The' 
physical effect of this proceeding is to cause the slag to break up into> 
porous particles (slag "sand"). Granulation has also certain chemical! 
effects, highly important from an economic point of view, which will 
be discussed later (p. 363). 
Methods of granulating the slag. — The success of the granulation! 
depends on bringing the slag into contact with the water as soon as- 
possible after it has left the furnace. The effects of the process will! 
be found to vary with (a) the temperature of the slag at the point off 
contact, (h) the temperature of the water, (c) the amount of waterr 
used, and (d) its method of application. 
Taking up the last point first, it may be noted that two general 
methods of application of the water have been used. In one the stream 
of slag as it issued from the furnaces is struck b}^ a jet of steam under 
pressure. This method, which was used at one time in the Middle- 
boro district, England, blows the slag into fine threads, with attached 
globules. It is, in fact, much the same as the process still used in the 
manufacture of mineral wool, which is elsewhere discussed. From an 
economic point of view it has the advantage of putting the slag in a 
condition in which it is easily pulverized by the grinding machinery: 
but it has certain inconveniences, and has been almost or entirely 
superseded by the method now to be mentioned. 
The second way in which the water may be applied is to allow the 
stream of slag as it issues from the furnace to fall into a trough con-i 
taining a rapidly flowing stream of cold water. Care must be taker 
that the fall into the trough is not too great, and that the stream oi 
water is deep enough and fast enough, for otherwise the slag wili 
a Ciments et chaux hydrauliques. 
