PART I. MATERIALS AND MANUFACTURE OF PORTLAND 
CEMENT. 
As noted in the Introduction, this bulletin is not intended to be a 
manual of cement manufacture, but a guide both to those who wish to 
locate available supplies of cement material and to those who wish to 
know whether materials occurring on their property are likely to 
be fit for such use. To persons of the first class, who usually are 
cement manufacturers, this first part of the bulletin will contain little 
of value; but it has seemed probable that such a sketch of cement 
technology will be serviceable to those who are not so well acquainted 
with the subject. In the discussion of the manufacture of Portland 
cement, stress has been laid only upon those processes which are 
directly influenced by the character of the raw materials used. The 
section on the mixing and grinding of the raw materials, for example, 
is much more detailed than the portion devoted to burning and clinker 
grinding. The subjects of cement testing and the uses of cement have 
been intentionally omitted. 
In the following section, various possible raw materials for Portland- 
cement manufacture will be taken up and their relative suitability for 
such use will be discussed. In order that the statements may be 
clearly understood it will be necessary to preface this discussion by a 
brief explanation regarding the composition of Portland cement. 
This subject will be treated in greater detail on pages 23-24. 
DEFINITION OF PORTLAND CEMENT. 
While there is a general agreement as to what is understood by the 
term Portland cement, a few points of importance are still open ques- 
tions. The definitions of the term given in specifications are, in con- 
sequence, often vague and unsatisfactory. 
Use of term Portland. — It is agreed that the cement mixture must 
consist essentially of lime, silica, and alumina in proportions which 
can vary but slightly, and that this mixture must be burned at a tem- 
perature which will give a semif used product— a " clinker." These 
points must therefore be included in any satisfactory definition. The 
point regarding which there is a difference of opinion is whether or 
not cements made by burning a natural rock can be considered true 
Portlands. The question whether the definition of Portland cement 
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