200 ANNUAL REPORT 
active element of cements, par excellence, which hydrates according to the 
following reaction: 
3CaOSiO,-+Aq—CaOSiO,2.5H,O-+2Ca(OH),. 
In addition to this compound, the Portland cement contains a tri-cal- 
cic aluminate, which is relatively unstable, but sets rapidly in water, and 
if present in too large amounts may cause the destruction of the cement. 
It hydrates according to the reaction: 
3CaOAl,O,-+-Aq=3CaOAl,O,12H,0. 
Chatelier thus considers Portland cement as composed of tri-calcium 
silicate, with a certain amount of calcium aluminate and ferrate, besides 
mono and dicalcium silicates. The hydration of the cement he expresses 
by the two reactions: 
2(3CaOS10, ) +9H,O=2CaOS10,5H,0+4Ca(OH ).. . 
Then a reaction takes place between the calcium hydrate, water and 
calcium aluminate forming a basic calcium aluminate: 
2€a@Al,O;== Ca(OH), -- 11H, O= 4. €aOAl_On2E ©: 
The hydrated basic aluminate determines the setting of the cement, 
while the hardening is fixed by the tri-calcium silicate. Chatelier fixes 
the amount of lime necessary for Portland cement by the expression: 
Dias sho NR ec 
SO, — NO, Fe,O,, 
3 
in which CaO, S10,, Al,O,, Fe,O, represent the number of equivalents 
of these substances present. The other limit he fixes by the expression: 
CaO 
SiO} NO) (0), 
SS 
The Work of Toernebohm.—Toernebohm practically checked the 
petrographic work of Chatelier, but arrived at a different composition of 
the compounds. According to him the Portland cement formula is: 
X (3CaOSiO, ) + (9CaO2Al,O;), 
in which the value of X fluctuates around 9. This investigator separated 
the minerals found by means of the Thoulet solution. 
The Work of Liamin—The next worker along petrographic lines 
was Liamin,* who produced a series of micro photographs of hardened 
————. 
*Report of the Imperial Russian Technical Society, 1897. 
