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CONCRETE CONCUBINAGE 211 case. Dr. Charles T. Jackson of Boston, after exhausting the air from the stone by means of a vacuum, found that it would absorb only about 16 per cent, of moisture. Under ordi- nary circumstances it may be considered as practically impervious to water, and is found to be quite as firm as most sandstones. Prof. Ansted of King's college, London, found that it would resist a crushing force of 4,200 Ibs. to the square inch, and that its tensile strength was equal to 360 Ibs. to the square inch ; while natural Portland limestone, Bath stone, and Caen stones possessed respectively only 201, 145, and 140 Ibs. tensile strength to the square inch. It is said that the best material that has yet been found for grindstones is that made by this process. The grains of sharp sand are held so firmly by the matrix of silicate of lime that they are capable of being made to cut away iron or steel with great rapidity. Ex- periments made by the Messrs. Donkin of Ber- mondsey showed that, compared with the best Newcastle stone, the Ransome stone had a ca- pacity of cutting away steel in the proportion of 50 to 1. The artificial stone possesses the ad- vantage, for large grindstones, of having more uniformity of structure than can be found in large blocks of natural stone, and it can be more readily formed into grindstones of various sizes. The American building block company pro- duce an artificial stone with silicious sand and lime, by subjecting the mixture to great pressure. There are two processes. The first, that of Fos- ter, is as follows : Rich lime is slaked with a small quantity of water, and mixed with moist sand in sufficient quantity to fill the voids. The mortar is then put in moulds and subjected to great pressure, which increases the ten- dency to formation of silicate of lime. The pressure should be so great that the grains of sand are forced into almost actual contact, so that when the chemical action is completed nothing but silica, and silicate of lime holding it together, will remain in the block ; the sur- plus of lime compounds being forced to the outside, where, by slowly hardening in the presence of air, they form a coating which does not detract from the value of the stone. Vanderburgh's process employs quick instead of slaked lime, which being mixed with moist sand is slaked by steam under pressure. A more complete union between the lime and sand is thus effected,.principally in consequence of the greater degree of heat employed ; and it is also found that the stone hardens more rapidly in Vanderburgh's than in Foster's pro- cess. The Union stone company of Boston, Mass., produce an artificial stone in imitation of several natural stones, the fabrication of which is founded upon the discovery of M. Sorel, a French chemist, that the double oxide and chloride of magnesium forms an excellent hydraulic cement. The materials used are magnesite (native carbonate of magnesia, which is found in various parts of the United States and Canada), chloride of magnesium, and sand, or powdered marble or other stone. The mag- nesite, reduced to caustic magnesia by burn- ing, is then mixed with sand or powdered stone in the desired proportions. A solution of chloride of magnesium is added, and the mix- ture is triturated in a mill, when it is turned into moulds and firmly rammed. Hardening commences immediately, so that the block may be removed as soon as the ramming is done. In consequence of the great advance in the knowledge of limes and cements that has taken place within the last few years, and the in- creased attention now being paid to the sub- ject by chemists, engineers, and architects, it is probable that various kinds of artificial stone may in the future be used as materials of con- struction, in many cases, with considerable ad- vantage. Full information in regard to the manufacture of concrete may be found in the " Practical Treatise on Coignet Be" ton and oth- er Artificial Stone," by Brevet Major Gen. Q. A. Gillmore, U. S. A. (New York, 1871) ; "Re- port on the Hydraulic Lime of Teil," by Leon- ard F. Beckwith, C. E. (New York, 1873) ; and Henry Reid's "Treatise on Concrete" (Lon- don, 1869). CONCUBINAGE (Lat. conculare, to cohabit), a term applied in ancient times to a quasi-conju- gal relation. Among the Hebrews the concu- bine was liable to be discarded, and to see her offspring excluded from the inheritance, though in most cases provisions were made for her and her children. The barrenness of a marriage often led to concubinage. Sometimes, with the wife's consent, her housemaid became the hus- band's concubine, to bring children into the family, but without his ceasing to stand in a marital relation to the wife. Subsequently the laws attempted to check excesses. The faith- lessness of a concubine was not punished as se- verely as that of a wife ; yet the line of demar- cation between the two was so narrow that the paramour of the concubine was considered as her husband and as the son-in-law of her father. The first act of a usurper consisted generally in appropriating the concubines of his predeces- sor. Among the Persians concubinage likewise prevailed. Darius was followed to the battle field by numerous concubines, arrayed in regal splendor. Among the ancient Egyptians priests were allowed only one wife; and though po- lygamy was not prohibited among the rest of the people, monogamy seems to have been the general practice. Among the Greeks the con- cubine was usually a native-born female, who occupied a position between a wife, a servant, and a harlot. Outrages on her person were resented as severely as if she had been a wife ; but she had to perform menial services, and af- ter the death of her quasi-husband she was often treated like a slave. The laws of Athens sanc- tioned the relation of concubinage, which how- ever was more trifled with among the Greeks than among the Hebrews; and the concu- bine was often made over to others, especially to guests of the house or to sons. In Rome