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"We learn from GcdiynanVs Messenger that an interesting paper on this subject has been submitted to the Academy of Sciences at Paris by M. Kuhlman, showing the advantage that may be derived from the combination of silicates with mortars and cements in general, and especially with those that are intended to resist the action of sea water. It is well known that the first effect of water on cements is that of forming hydrates, after which a gradual contraction takes place, producing a degree of hardness which increases in proportion as the contraction is slower, and there is more silica or alumina in the cement. Now M. Kuhlman has observed that if alumina or its silicate, or else magnesia, whether caustic or carbonated, be kneaded into a paste with a solution of silicate of potash or soda, the compounds resulting therefrom will bear a perf e resemblance to the natural silicates, such as feldspar, talcous shale, magnesite, &c, and will, by repose and slow contraction, become hard and"Bemi-transparent, resisting in a high degree the corrosive effects of water. If slaked lime be added to the said compounds they acquire the properties of hydraulic cements. M. Vicat, Jr., having shown, that calcined magnesia added to a cement would resist the action of sulphates of magnesia, M. Kuhlman has endeavored to turn this observation to account, by mixing calcined dolomites (which contain magnesia with mortar, with the addition of alkaline silicates. This composition he finds very advantageous, since most of the salts contained in sea water must contribute towards the preservation of such cements. In fact, the chloride of magnesium, as well as the sulphate of magnesia, will be decomposed, and form a layer of silicate of magnesia on the surface of the cement; in the same manner the sulphate of lime must, being in contact with the silicate of potash or soda, form the silicate of lime; and all the silicates strongly resist the action of sea water. As for sea salt, which is a chloride of sodium, M. Kuhlman proves that in the proportion in which it exists in sea water it will slowly decompose the silicate of potash contained in the cement, and leave the silica free. The compositions proposed have, therefore, the singular property not only of resisting the corrosive qualities of sea water, but of actually becoming more insoluble the longer they are in contact with it. A cement composed of 30 parts of rich lime, 50 of sand, 15 of uncalcined clay, and 5 of powdered silicate of potash, is recommended by M. Kuhlmann as having the requisite hydraulic properties. In marine constructions care should be taken to add an excess of silicate to those portions of cenrent which are exposed to the immediate contact of the sea. M. Kuhlman is an old and valued correspondent of ours, and we are pleased to see that he is still devoting his profound chemical knowledge and ability, to the development of improvements having a practical and useful tendency.
