The letter c is not used by itself in re-writing for pronunciation, s or k being used instead. The only consonantal symbols, therefore, that require explanation are the following: Educated at Geneva, he resided a considerable time abroad, especially in Germany, and was much influenced by German thought and science.
Passow Cement is a recent product which is in a class by itself. It differs from ordinary slag cement see above in that it is not a pozzuolanic cement depending on the interaction of granulated slag and lime.
The particular method of granulating slag for Passow cement produces a material which sets per se and attains a strength comparable with that of Portland cement. Passow cement has been successfully made from slag of different compositions in Germany, England and America.
No doubt in times of remote antiquity it was found that the jointing of masonry Uses of hydraulic cements. Ordinary mortar failed in such positions; mortar made from lime prepared from limestones or chalks containing a little clay was found to stand; mortar made from lime mixed with trass or similar active silicious material was also found to stand.
On this observation rests the whole of the present enormous employment of hydraulic cements. It was a natural transition to utilize these cements not merely for jointing masonry but also for making concrete, and the only reason why hydraulic cements, as distinct from cements which are not hydraulic e.
Their use in above-water work is checked by the low price of common brick.
Even in such work, where it would be thought that masses of burnt clay would be the cheapest conceivable material, concrete is at least on level terms with its rival. It must be remembered that one of the great advantages of concrete is that five-sixths of its total mass may be provided from local sand and gravel, on which no carriage has to be paid.
The cement, on which alone freight is to be reckoned, converts these from loose incoherent material into a solid stone. Thus it comes about that the largest use of cement is for manufacturing concrete for dock and harbour work, and for the making of foundations.
It is also employed for the building of light bridges, floors, and pipes constructed of cement mortar disposed round a skeleton of iron rods.
Such composite structures take advantage at once of the high tensile strength of iron and of the high compressive strength of cement mortar. Good hydraulic cements are highly permanent materials provided certain conditions be observed.
It might be supposed that hydraulic cements from their nature would be indifferent to the action of water, but this is only true if the structures of which they form part are sufficiently compact.
In this case the action of the water is checked by the film of carbonate of lime which eventually forms oh the surface of calcareous cement.
This, together with the compactness of the mortar, hinders the ingress and egress of water, and prevents the dissolution and ultimate destruction of the cement.
But where the concrete or mortar is not well made and is porous, the continual passage of water through it will gradually break up and dissolve away the calcareous constituents of the cement until its strength is utterly destroyed. This destructive action is increased if the water contains sulphates or magnesium salts, both of which act chemically on the calcareous constituents of the cement.
As sea-water contains both sulphates and magnesium salts, it is especially necessary in concrete for harbour work to take every care to produce an impervious structure. There are various minor external causes for the failure and ultimate destruction of cement mortar and concrete, but their discussion is a matter for the specialist.
Failure from inherent vice in the cement has been already touched on; it can always be traced to want of skill and care in manufacture. The raw material is gypsum q. The mode of preparation is to calcine the gypsum at temperatures which depend on the class of cement to be produced.
To produce plaster of Paris European practice consists in baking the mineral in ovens, and in America in heating it in kettles. In the light of this knowledge the mode of setting of plaster of Paris becomes clear.
The setting is rapid, occupying only a few minutes, and is accompanied by a considerable expansion of the mass. There is reason to suppose that the change described takes place in two stages, the gypsum first forming orthorhombic crystals and then crystallizing in the monosymmetric system.
Gypsum thus crystallized is in its normal monosymmetric form, more stable under ordinary conditions than the orthorhombic form. Correlatively in its process of dehydration to form plaster of Paris, monosymmetric gypsum is converted into the orthorhombic form before it begins to be dehydrated.
The principles which govern the preparation and setting of the other class of calcium sulphate cements, that is, cements of the Keene class, are not fully understood, but there is a fair amount of knowledge on the subject, both empirical and scientific.
Instead of alum various other salts, e. It seems probable that the effect of the salts is inconsiderable, and that the governing condition is the temperature at which the cement has been burnt.
All cements having calcium sulphate as their base are suitable only for indoor work because of the solubility of this substance. They form excellent decorative plasters on account of their clean white colour and the sharpness of castings made from them, this latter quantity being due to their expansion when setting.
Butler, Portland Cement London, ; E. A strong cement for alabaster and marble, which sets in a day, may be prepared by mixing 12 parts of Portland cement, 8 of fine sand and 1 of infusorial earth, and making them into a thick paste with silicate of soda; the object to be cemented need not be heated.Search the history of over billion web pages on the Internet.
An´apæst, in prosody, a foot consisting of two short and one long syllable, or two unaccented and one accented syllable, e.g. An´aplasty, a surgical operation to repair superficial lesions, or make up for lost parts, by the employment of adjacent healthy structure or tissue. An ordinary kiln, which will contain about 50 tons of slurry and 12 tons of coke, will take two days to get fairly alight, and will be another two or three days in burning out.
Therefore, allowing adequate time for loading and unloading, each kiln will require about one week for a complete run. The myth of Eros and Psyche is probably one of the best love stories in classical mythology.
Eros, son of Aphrodite, was the personification of intense love desire and he was depicted throwing arrows to people in order to hit their heart and make them fall in love.
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