34 ANNUAL REPORT 
investigators they may be selected as representing the characteristic be- 
havior of ferric oxide. 
On burning the mixture CaOFe,O, in the Seger furnace till partially 
fused it assumed a graphite-like appearance, and when ground and mixea 
with water it formed a pat of a fine mahogany-like color. It set in four 
hours. After five hours more it was hard enough to be placed in water. 
After several months the pats became quite hard, but did not show as 
inuch strength as the corresponding alumina compound. The mixture 
(2CaO) Fe,O,, burnt to softening, which took place at a white heat, showed 
a decided crystalline structure. After grinding and making up with water 
the pats set in fifteen minutes and in one to two hours had become quite 
solid and hard. After one week in water they softened somewhat and lost 
their original strength. When dried in a dessicator they became harder 
again, but did not reach the hardness of the corresponding alumina com- 
pound. More favorable results were obtained with impure materials, that 
is, with reagents containing some silica and alumina. 
We can say, therefore, that the iron-lime compounds are very similar 
to the alumina-lime products, though much more feeble in their hydraulic 
reaction. One function in which iron is more effective is the greater 
fusibility produced by it. While a lime silicate like (3CaO) SiO, is prac- 
tically infusible excepting in the electric furnace and the oxy-hydrogen 
blowpipe, it is at once rendered more fusible by the addition of alumina 
and much more fusible by adding ferric oxide. ‘This is observed quite 
strikingly in using as the clay base a pure clay, like kaolin, or an impure 
variety containing more or less iron. Only by the presence of iron is it 
possible to burn Portland cement at commercially feasible temperatures. 
In addition the oxides of iron seem to counteract the phenomenon known 
to the cement men as “dusting,” and of late the surprising resisting power 
of ferruginous cements to the action of sea water has aroused general 
attention. 
LIME. 
This important material, which constitutes the greatly preponderating 
ingredient of all hydraulic cements, occurs in nature in enormous quan- 
tities, chiefly as calcium carbonate, from the almost chemically pure form 
of calcite and aragonite, in various degrees of purity, down to the loamy 
and impure marl clays. Pure calcium carbonate consists of 56 parts cal- 
cium oxide and 44 of carbon dioxide, which begins to be expelled at about 
600° C., the evolution of the gas being completed at 1040° C. in all lime- 
stones. ‘The harder, more dense and crystalline the carbonate of lime is 
the slower and more reluctantly will the carbon dioxide be evolved. By the 
presence of silica or silicate of alumina the decomposition of the carbonate 
is accelerated, and hence more impure limestones are easily overburnt, as 
the practical lime burner says. 
