226 : ANNUAL REPORT 
owing to its solubility in water, 1 part of anhydrous sulphate being 
soluble in 488 parts of water at 18° C. This apparently slight solu- 
bility after all is not to be neglected, especially since its solubility is 
increased most decidedly by the presence of other salts like sodium 
Enioaals, calonbhan Caloris, cic, Alas ae Ais Co a 4.5 ner Gault, column 
of sodium chloride can dissolve 0.674 grams of gypsum for each 100 
cubic centimeters. 
LIMESTONE AND CALCAREOUS MATERIALS. 
1. These should be fine grained and uniform in composition and 
structure. 
2. The magnesia should be low enough so that in the cement a 
content of 3 per cent. of magnesia is not exceeded. 
3. The alumina content should not be high enough to disturb the 
proper silica-alumina ratio in the cement. 
4. The content of ferric oxide must not be so high as to increase 
the amount of ferric oxide in the cement beyond 4 per cent. 
5. It should be low in sulphur and free from concretionary iron 
sulphide. 
In the consideration of calcareous materials, the most important ques- 
tion is that of the magnesia content, as the restricting clause in regard to 
the magnesia rules out many otherwise excellent materials. In 
many cases the limit of magnesia is exceeded but slightly and it seems a 
pity that such materials should be rejected. The fact is that it is unjust 
to throw out a material on account of one or two per cent. of magnesia 
in excess over the three per cent., as many tests have shown that a 
magnesia content even up to 7 per cent. in an otherwise well propor- 
tioned cement has no deleterious influence. It might be well to cite 
some investigations covering this point. Dyckerhoff’s elaborate experi- 
ments, it is true, condemned magnesia. His work included the duplicate 
testing of various contents, both in regard to the tensile strength for 
periods up to five years, and the measurement of the increase in 
volume in terms of the linear expansion of a bar of cement I00 mm. 
long, made by careful micrometer measurements. The results obtained 
by him are summarized in the curves on pages 227-9. 
Meyer, on. the other hand, denies most emphatically that magnesia 
is a dangerous constituent. Blaese allows as much as Io per cent. of 
magnesia. Tetmayer reports two vitrified cements of the analysis shown 
in table on page 230, as having stood the tests for constancy of volume. 
The tensile and crushing strength expressed in kilograms per sq. cm. 
were found by him as given in the second table on page 230. 
