CEMENT.

South Canterbury Times, Issue 2530, 30 April 1881, Page 2

CEMENT.

ITS DISCOVERY AND MANUFACTURE. I (By J. Bbough Stansell.) Considerable attention has of late been devoted to what is known as Portland or hydraulic cement. It ;'s doubtful if in any part of the world its importance has become move thoroughly appreciated than in this colony. The necessity for improved harbor accommodation has already led to the expenditure annually of hundreds of thousands of pounds on this material, and unless active measures are taken to promote its manufacture in the colony, this expenditure is likely to go on increasing from year to year instead of diminishing. The Government has lately recognised the importance of developing the manufacture of this material by offering a substantial bonus for its production. Believing that the object in view may be promoted in a no less practical way by awakening general attention to this particular form of industry, I have prepared, somewhat hastily, the following paper on the subject. If it tends to stimulate enterprise, and excite experiment in a colony which, I am confident, is richly endowed with the minerals requisite for the production of this valuable building agent,l shall feel that the slight effort I have put forth has been fully rewarded: — Ancient and extinct nationafities have successfully used cements and mortars, as the existing remains of their engineering and architectural works testify. These remains, of a varied and interesting character, now show us how much of their stability and permanence ia due to the quality of the cementing agent by which the building materials were put together. Hence the character and quality of ancient structures has excited admiration and occasioned puzzling guesses as to the composition and preparation of the mortars used. Lime mortar, as a binding material, was used by the Phoenicians in the Island of Cyprus, as shown by the temple ruins of Lunarca. The Egyptians in the Nile Valley are supposed to have made use of the river mud and burnt gypsum as a mortar in budding the Pyramids. The Assyrians had recourse to aspbalte as their cementing agent in the construction of Babylon and Ninevah, The asphalte of the Red Sea was well known to the ancients. It was a'so obtained in pits and springs near the Rivers Euphrates and Tigris. According to the writings of Vitruvius, the Romans used fat limes in combination with various volcanic products. With such ancient testimonies as we have, it is difficult to say when and where the firni mortals were used. The term or name “ mortar " is of Roman derivation, from the fact of these practical people using a “ movtaumn ” to secuie the perfect horaogenity of the building material. Professor Hay ter Lewis states that the old Roman works were composed entirely of concrete or rubble ; the Meduevals used it ri the same way,and it was as hard as a rock. Some fine Roman remains could be seen at Pevensey and Richmond, and the work of the Medisevals could be seen in the grand old keep at Rochester Castle, where not only the walls but the staircases were built of concrete. It was stated bj the old writers chat the Romans depended entirely, or chiefly, not upon stone and bricks but upon cements, and Vitruvius said that certain works were stronger than others simply because they admitted of a larger quantity of cement being used. He had lately brought from Egypt a portion of the mortar used in the great Pyramid, which was at least five or six thousand years old. It was quite friable, and therefore it was not age which gave strength to the materials used. In modern times the first mention of a cement, named in consequence of its fancied resemblance to Portland stone, Portland cement occurs in the specification of a patent granted to Joseph Aspdin, a bricklayer, of Leeds, dated Oct., 21, 1824. The cement originally made by Aspdin does not, however, appear to have been a true Portland cement, nor was his process identical with that which has since been generally adopted in the production of this material. It is probable that the son of Aspdin, who established a manufactory at Northfleet, on the Thames, a few years after bis father’s discovery, was one of the first, if not the first, makers of cement in the London district, and may probably be considered the founder of the Portland cement in the London district.

The experiments of John Smeaton, C.E., in 1757, dispelled the darkness surrounding the subject of mortars, and their behaviour under varied circumstance .. Tli© noooooity for n hilly reliable mortar for f e building of the Eddystone Lighthouse, capable of withstanding the influence of sea water, and possessing also the power of resisting the destructive action of violent storms, was a problem of much difficulty, but which this illustrous engineer successfully solved. Those who have read the story of that work during its preliminary stages, and are aware of the protracted and dangerous process of its construction, will readily understand the anxiety of the directing engineer, on whom the whole responsibilty devolved. It is possible that many persona may fail to appreciate the great value of these experiments. The following testimony to the value of Smeaton’s experiments is taken from a work on “ Hydraulic Mortars ” and published at Leipsig in 1869, by Dr Michaelia “ A century has elapsed since the celebrat'd Smeaton completed the building of the Eddystone Lighthouse. Not only to sailors, but the whole human race is this lighthouse a token of useful work, a light in a dark night. In a scientific point of view, it has illuminated the darkness of aimost wo thousand years.

“ The Eddystone Lighthouse is the foundation upon which our knowledge of hydraulic mortars has been erected, and it is the chief pillar of modern architecture, Smeaton freed us from the fetters of tradition by showing us that the purest and hardest limestone is not the best for hydraulic purposes, and that the cause of hydraulicity must be sought for in the argillaceous admixture.

“ It was a long time before men of science confirmed the statement of the English engineer or corrected the ideas ou the hardening of hydraulic mortars,

on account of the imperfect state of chemistry at that time. How could science subsequently keep pace with practical progress ? For even at present, though we hare possessed for about half a century the most excellent hydraulic mortars, the hardening process is not yet explained.” Major General Pasley in the preface to his work on cements, dated 1838, says of Smeaton “Of all the authors who have investigated the properties of calcareous mortars and cements from lime immemorial to the present day, our countryman, Smeaton, appears to me to have the greatest merit, for although ho found out no new cement himself, he was the first who discovered, in or soon after the year 1756, that the real cause of water-acting properties of limes and cements consisted in a combination of clay with the carbonate of lime ; in consequence of having ascertained by a very simple sort of analysis, that there was a proportion of the former ingredient in all the natural limestones, which, on being calcined, developed that highly important quality, without which walls exposed to water go to to pieces, and those exposed to air and weather only are comparatively of inferior strength. By this memorable discovery Smeaton overset the prejudices of more than two thousand ye. rs, adopted by all former writers, from Vitruvius, in ancient Rome, to Belidor, in France, and Semple, in this country, who agreed in maintaining that the superiority of lime consisted in the hardness and whiteness of t-e stone, the former of which may or may not be accompanied by water-setting or powerful cementing properties, and the latter of which is absolutely incompatible with them. It is pleasing to find that the engineer and the lighthouse are so closely identified that no one cares to recollect under what reign it was built. The name of the engineer and not that of the king descends to posterity, receiving Tie credit of his labors. (To be continued.)