

PORTLAND CEMENT: PRELIMINARY STATEMENTS. 295 



Recurring to Aspdin's work, it is to be noted that his original patent 

 did not specify the percentages in which the two raw materials were 

 to be mixed, and that it also omitted any mention of the high tem- 

 perature necessary to secure a good product. The earliest Portland 

 was probably, so far as its properties were concerned, like one of our 

 poorer low-limed grades of natural cements. These defects were, how- 

 ever, overcome when Aspdin took up the manufacture on a commercial 

 scale, and before 1850 the new product had established its value. In 

 later chapters further details may be found concerning the early history 

 and growth of the industry, both in Europe and in America. 



Present use of the term "Portland". While there is at present a 

 fairly close general agreement as to what is to be understood by the 

 term " Portland cement", a few points of importance are still open 

 questions. Partly in consequence of this uncertainty, but more largely 

 because of the intense imitativeness of specification-makers, the defini- 

 tions of the term given in specifications and text-books are usually 

 vague and unsatisfactory. 



It is commonly agreed that the cement mixture must consist essen- 

 tially of lime, silica, and alumina in proportions which can vary but 

 slightly, and that this mixture must be burned at a temperature which 

 will give a semi-fused product a " clinker ". These points must therefore 

 be included in any satisfactory definition. The principal point regard- 

 ing which there is a difference of opinion is whether or not cements 

 made by burning a natural rock without previous mixing and grinding 

 can under any circumstances be considered true Portlands. The ques- 

 tion as to whether the definition of Portland cement should be drawn 

 so as to include or exclude such products is evidently largely a matter 

 of convention; but, unlike most conventional issues, the decision has 

 very important practical consequences. The question at issue may 

 be stated as follows: 



If we make artificial mixture of the raw materials and a very high 

 degree of burning the criteria on which to base our definition, we must 

 in consequence of that decision exclude from the class of Portland 

 cements certain well-known products manufactured at several points 

 in France and Belgium by burning a natural rock without previous 

 fine crushing or artificial mixture and at a considerably lower tem- 

 perature than is attained in ordinary Portland-cement practice. These 

 "natural Portlands" of France and Belgium have been considered Port- 

 land cements by some of the most critical authorities, though all agree 

 that they are not particularly high-grade Portlands. So that a definition 

 based upon the criteria above named will of necessity exclude from 



