370 The Philippine Journal of Science 1922 
All four cements when gauged with water alone show a de- 
crease in tensile strength between the l-year and the 5-year 
periods. The general effect of the various salts is to lower the 
tensile strength—usually less than 50 pounds. In some cases, 
there is an increase in strength. The results are not sufficiently 
regular to permit any definite conclusions as to the relative effect 
of the various ions present. Cement III suffered the greatest 
loss in strength. A comparison of the chemical] analysis of the 
four cements offers no clue as to why this should be the case. 
In the physica] tests this cement is higher in fineness than any 
of the others. Up to one year its tensile strength is much 
higher than that of the others, but it falls off considerably 
between the first and the fifth years. 
The results given in this paper and also those obtained by 
other investigators since this work was carried out indicate that 
in general—in the case of concrete, at least—ordinary inorganic 
substances are less likely to affect the strength of cement when 
they are used in the mixing water than when present in water 
to which hardened concrete is exposed. In fact, this is true 
of many substances, both organic and inorganic. Recently a 
series of concrete specimens was made, using a number of 
industrial waste waters.’ These waters contained large quan- 
tities of various substances in solution, and it was expected 
that they would show very erratic results. However, in most 
cases the specimens already broken have not shown any ill effects. 
At first it seems peculiar that a given water should have less 
effect when mixed with concrete than when brought into contact 
with the finished concrete because, of course, there is much 
more intimate contact in the former case. In the tests made 
in the Bureau of Science, a normal solution of sodium sulphate 
had little or no effect on either of the four cements used, while 
concrete specimens exposed to much more dilute solutions of 
the same salt may become completely disintegrated. The ex- 
planation for this is found in the relative quantities of the 
foreign substance present. The amount of a substance in solu- 
tion that can be added to cement through the agency of the 
mixing water is relatively small. For example, when briquettes 
were made, using normal sodium sulphate solutions as the mix- 
ing water, the sulphuric anhydride added was only approximately 
1.4 per cent of the calcium oxide present in the cement. When 
concrete is exposed to waters containing sulphates in the field, 
usually the amount of sulphuric anhydride present in relation 
*From a paper by D. A. Abrams which has not yet been published. 
