This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The third class is one imported from Belgium under various brands carrying English names, such as "Eagle," "Star," etc., the packages, however, showing the place of manufacture. These cements are generally coarse and of low grade - possibly the factory's second grade, on which the manufacturer does not care to put his regular brand.
English cement is practically out of the market.
A few brands of German remain, like the "Dykerhoff," which commands a high price and for which there is a limited demand from users who believe there are no other brands from which quite as good results can be obtained. For our purposes, however, the second and third classes need not be considered; the range in No. 1 is wide, and little if anything is gained in price in using Nos. 2 and 3.
On important work, tests should be made to determine the fineness of grinding, specific gravity, time of initial and final set, soundness, the proportion of silica to lime, and the amount of sulphur and magnesia. Tests are also made of tensile strength; but as this is a quality never required of cement, and this test only indirectly bears on other necessary qualities; and as the presence of matter which is apt to cause final disintegration, tends often - in the early stages of use - to increase the tensile strength, such tests should be in no way relied on.
In this paper, only three tests which it is possible for the student to make with appliances easily obtained, will be considered.