Questions are frequently raised in connection with sea-coast works as to whether any deleterious effect will result from using sea-water for mixing the concrete or from using sand and shingle off the beach; and, further, whether the concrete, after it is mixed, will withstand the action of the elements, exposed, as it will be, to air and sea-water, rain, hot sun, and frosts. Some concrete structures have failed by decay of the material, principally between high and low water mark, and in order to ascertain the probable causes and to learn the precautions which it is necessary to take, some elaborate experiments have been carried out. To appreciate the chemical actions which may occur, it will be as well to examine analyses of sea-water and cement. The water of the Irish Channel is composed of Sodium chloride.................... 2.6439 per cent. Magnesium chloride................. 0.3150 " " Magnesium sulphate................. 0.2066 " " Calcium sulphate................... 0.1331 " " Potassium chloride................. 0.0746 " " Magnesium bromide.................. 0.0070 " " Calcium carbonate.................. 0.0047 " " Iron carbonate..................... 0.0005 " " Magnesium nitrate.................. 0.0002 " " Lithium chloride................... Traces. Ammonium chloride.................. Traces. Silica chloride.................... Traces. Water.............................. 96.6144 -------- 100.0000 An average analysis of a Thames cement may be taken to be as follows:-- Silica................................ 23.54 per cent. Insoluble residue (sand, clay, etc.)............................ 0.40 " Alumina and ferric oxide............... 9.86 " Lime.................................. 62.08 " 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