Do, ANNUAL REPORT 
: oe ee eee) Se 
a. Shea oS 3 43 o8 . oe Formula. 
1) aes Hy sO ga aS 5 nS 
& 28 SEO | Reabs | & 
800 5.94 8.94 14.88 5.60 | CaQ, O70, 
900 6.44 16.40 | 22.84 1.30 | CaO, 0.36810, 
1,100 | Wk NG O2 | BB 1s con | CXO, 0.87780, 
1-200) || 22210) |) 18,04 | 404 sooo | CxO, 1.1490, 
LOO | 22.733 18.04 | 40.77 eer CaO, 1.18810, 
At 800° apparently all of the free calcium oxide has combined with sil- 
ica, while at 900° there is evidently some lime uncombined, so that the for- 
mula appears distorted. It is evident that the lime has united with no less 
silica than at 800°, but more calcium oxide is available than at the latter 
temperature. This is indicated also by the decided caustic property 
of this mixture. The best index of the activity of the lime is the amount 
of silica rendered soluble, especially if for 800° and goo° the carbon 
dioxide is eliminated by calculation which will make the soluble silica 
6.36 and 6.52 per cent. respectively. The mixtures at 800° and 900” 
showed caustic properties, especially the goo° sample, while those of the 
other samples were lumpy and not noticeably caustic. 
It is quite evident that the action of lime upon finely ground free 
silica is reasonably well represented by these experiments, and it appears 
that at the highest temperature employed, 1300° C., less than one molecule 
of lime is required to render soluble or available for combination one 
molecule of free silica, the proportion being 0.847 molecule of calcium 
oxide to one molecule of silica. This throws additional light on the 
Roman cement reaction, and explains why such cements may be so low 
in lime, the function of the latter being simply the “unlocking” of the 
inert quartz, and the work also indicates that there should be no difficulty 
in assimilating the quartz of clays, provided the latter is ground fine 
enough, so that it is not absolutely necessary to depend upon naturally 
fine clays. The practice of shipping naturally fine clays considerable 
distances is hence not a necessity, if sand or sandstone in any shape is 
available. On the other hand it encourages the use of silicious clays in 
preference to clays comparatively high in alumina. 
It must also be realized that in a cement the attack of lime on silica 
is much more vigorous owing to the formation of a more fusible. cal- 
careous magma in which silica is bound to be quite soluble. 
