Magnesia............................... 1.20 "
Sulphuric anhydride.................... 1.08 "
Carbonic anhydride and water........... 1.34 "
Alkalies and loss on analysis.......... 0.50 "
-----
100.00


The following figures give the analysis of a sample of cement
expressed in terms of the complex compounds that are found:--


Sodium silicate (Na2SiO3)........ 3.43 per cent.
Calcium sulphate (CaSO4)......... 2.45 "
Dicalcium silicate (Ca2SiO4).... 61.89 "
Dicalcium aluminate (Ca2Al2O5).. 12.14 "
Dicalcium ferrate (Ca2Fe2O5)..... 4.35 "
Magnesium oxide (MgO)............ 0.97 "
Calcium oxide (CaO)............. 14.22 "
Loss on analysis, &c............. 0.55 "
-----
100.00


Dr. W. Michaelis, the German cement specialist, gave much
consideration to this matter in 1906, and formed the opinion
that the free lime in the Portland cement, or the lime freed in
hardening, combines with the sulphuric acid of the sea-water,
which causes the mortar or cement to expand, resulting in its
destruction. He proposed to neutralise this action by adding to