Bulletin, Ausgabe 2


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Seite 120 - But, so far as the writer is aware, no attempt has been made to determine experimentally the capacity of dements to receive instruction.
Seite 263 - ... feet. Toughness, as understood by road builders, is the adhesion between the crystal and fine particles of a rock, which gives it power to resist fracture when subjected to the blows of traffic. This important property, while distinct from hardness, is yet intimately associated with it, and can in a measure make up for a deficiency in hardness. Hardness, for instance, would...
Seite 263 - Binding power is thus, probably, the most important property to be sought for in a road-building rock, as its presence is always necessary for the best results. The hardness and toughness of the binder surface more than of the rock itself represents the hardness and toughness of the road, for if the weight of traffic is sufficient to destroy the bond of cementation of the surface, the stones below are soon loosened and forced out of place. When there is an absence of binding material, which often...
Seite 160 - The first time this method was used, air under a pressure of 80 pounds was admitted into the cavity which had previously been extended to a distance of 100 feet from the lift hole. The power of the air, however, was too great for the easily splitting stone and the cleavage turned abruptly to the surface. In the next hole, however, the compressed air was admitted very gradually and the stone could soon be heard cracking in all directions, and in about half an hour the cleavage came to the surface...
Seite 263 - This important property, while distinct from hardness, is yet intimately associated with it, and can in a measure make up for a deficiency in hardness. Hardness, for instance, would be the resistance offered by a rock to the grinding of an emery wheel ; toughness, the resistance to fracture when struck with a hammer. Cementing or binding power is the property possessed by the dust of a rock to act, after wetting, as a cement to the coarser frag; ments composing the road, binding them together and...
Seite 159 - A sheet of several acres in extent may be raised in this manner, affording a bed plane approximately horizontal, to which the quarrymen can work, thus securing stone of any required thickness.
Seite 182 - They are not numerous in any of the openings, and, as a rule, they do not measure more than a few inches across. Quartz veins of large dimensions are numerous over the crystalline area of the State.
Seite 45 - County has been used mostly for street purposes in the form of blocks ; for coping and bridges ; and to a less extent as a building stone. It has been shipped to numerous places in Virginia and North Carolina, especially to the eastern towns in these two States.
Seite 111 - University in Washington, DC This grade of pink granite is in much demand in Chicago and other northern and central cities for use as monumental stock.
Seite 3 - The impact of the hammer breaks up the granules on the immediate surface so that the light falling upon it is reflected, instead of absorbed, and the resultant effect upon the eye is that of whiteness. The darker color of a polished surface is due merely to the fact that through careful grinding all these irregularities and reflecting surfaces are removed, the light penetrating the stone is absorbed, and the effect upon the eye is that of a more or less complete absence of light or darkness. Obviously...

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