216 ANNUAL ERERORE 
Dr. Hart gives the heats of neutralization of the various silicates in 
the following table: 
As clinker. eee Dehydrated. 
Calories. Calories. | Calories. 
Wollastonite ....... Sermehis ie are Sun we 13.0 
Artificial CaOSiO,.......... 20.0). 234.7 187.5 
2CAOSIOM Seo ews ee ee By 45) 60) 326.0 BVA oo 
SCAOSI OR tans fat eee anes Pyd),, 1 266.0 DU Oo® 
Ca@iAll Oat ee eres ae pe teeters 41.4 72.7 238.7 
DONO Ose osc ce- Ey are | 201.0 240.2 356.6 
BC AO ANG, 8 peor mace renee eegn | 428 .2 266.6 
me a a 
The question of whether Portland cement consists of compounds of 
silica with lime or whether it is simply a colloid mixture of decomposed 
clay and lime was attacked by Dr. W. Ostwald* from the thermo-chemical 
standpoint by determining the heats of solution in hydrochloric acid 
(5 grams cement in 500 cc. acid, specific gravity 1.06) using a beaker 
calorimeter. His results have shown that Portland cement must consist 
essentially of compounds of lime and the constituents of clay. 
Another interesting more recent investigation was carried on by 
W. Richter** who found that Portland cement did not react with phenol- 
phtalein, but did as soon as ignited calcium oxide was added. The latter 
did not slake like ordinary lime, but broke down to a granular powder. 
With water the ignited lime set like cement and showed but a slight rise in 
temperature; it stood the boiling test and reacted with phenol-phtalein. 
Richter concludes, that all the lime in cement is combined. He claims that 
there can be no aluminate of lime,as calcium aluminates were found to react 
with phenol-phtalein. He further prepared a tri-calcium silicate not react- 
ing with phenol-phtalein. The boiling test he does not consider a sufficient 
criterion for the presence of free lime. The di-calcium silicate he found 
to possess slight cementing qualities, but it did not stand the boiling test. 
On grinding the di-calcium silicate with crystalline calcium owxide, a 
cement was obtained which hardened like a tri-calcium silicate cement. 
Richter thinks that the hydration reaction proceeds as follows: 
3CaOS10,+H,O=2CaOSi0,+Ca(OH),. 
2CaOSiO,+Ca(OH),.+H,O=CaOSi0,+2Ca(OH).,. 
In 1899 Dr. Michaelis* published a startling theory which contra- 
dicted all the previous assumptions. He claimed that the hydraulic 
hardening is a combination of chemical and physical processes. [or 
*Tonindustrie Zeitung, 1888, No. 46. 
** Tbid, 1908, No. 120. 
