II.

LIME.

38. CLASSIFICATION OF LIME.-Considered as a building material, lime is now usually divided into three principal classes: Common or Air lime, Hydraulic lime, and Hydraulic, or Water cement.

39. Common, or air lime, is so called because the paste made from it with water will harden only in the air.

40. Hydraulic lime and hydraulic cement both take their name from hardening under water. The former differs from the latter in two essential points. It slakes thoroughly, like common lime, when deprived of its carbonic acid, and it does not harden promptly under water. Hydraulic cement, on the contrary, does not slake, and usually hardens very soon.

41. Our nomenclature, with regard to these substances, is still quite defective for scientific arrangement. For the limestones which yield hydraulic lime when completely calcined, also give an hydraulic cement when deprived of a portion only of their carbonic acid; and other limestones yield, on calcination, a result which can neither be termed lime nor hydraulic cement, owing to its slaking very imperfectly, and not retaining the hardness which it quickly takes when first placed un

der water.

M. Vicat, whose able researches into the properties of lime and mortars are so well known, has proposed to apply the term cement limestones (calcaires à ciment) to those stones which, when completely calcined, yield hydraulic cement, and which under no degree of calcination will give hydraulic lime. For the limestones which yield hydraulic lime when completely calcined, and which, when subjected to a degree of heat insufficient to drive off all their carbonic acid, yield hydraulic cement, he proposes to retain the name hydraulic limestones; and to call the cement obtained from their incomplete calcination under-burnt hydraulic cement (ciments d'incuits), to distinguish it from that obtained from the cement stone. With respect to those limestones which, by calcination, give a result that partakes partly of the properties both of limes and cements, he proposes for them the name of dividing limes (chaux limites.)

The terms fat and meager are also applied to limes; owing to the difference in the quality of the paste obtained from them with the same quantity of water. The fat limes give a

paste which is unctuous both to the sight and touch. The meager limes yield a thin paste. These names were of some importance when first introduced, as they served to distinguish common from hydraulic lime, the former being always fat, the latter meager; but, later experience having shown that all meager limes are not hydraulic, the terms are no longer of use, except to designate qualities of the paste of limes.

42. Hydraulic Limes and Cements. The limestones which yield these substances are either argillaceous, or magnesian, or argillo-magnesian. The products of their calcination vary considerably in their hydraulic properties. Some of the hydraulic limes harden, or set very slowly under water, while others set rapidly. The hydraulic cements set in a very short time. This diversity in the hydraulic energy of the argillaceous limestones arises from the variable proportions in which the lime and clay enter into their composition.

43. M. Petot, a civil engineer in the French service, in an able work entitled Recherches sur la Chauffournerie, gives the following table, exhibiting these combinations, and the results obtained from their calcination.

44. The most celebrated European hydraulic cements are obtained from argillaceous limestones, which vary but slightly in their constituent elements and properties. The following table gives the results of analyses to determine the relative proportions of lime and clay in these cements.

Table of Foreign Hydraulic Cements, showing the relative proportions of Clay and Lime contained in them.

English, (commonly known as Parker's, or Roman cement).
French, (made from Boulogne pebbles).

55.40 44.60

54.00 46.00

The hydraulic cements used in England are obtained from various localities, and differ but little in the relative proportions of lime and clay found in them. Parker's cement, so called from the name of the person who first introduced it, is obtained by calcining nodules of septaria. The composition of these nodules is the same as that of the Boulogne pebbles found on the opposite coast of France. The stones which furnish the English and French hydraulic cements contain but a very small amount of magnesia.

45. A hydraulic cement known as natural Portland cement is manufactured in France, at Boulogne, where the stone, which is very soft, is found underlying the strata which furnish the Boulogne pebbles.

46. The best known hydraulic cements of the United States are manufactured in the State of New York. The following analyses of some of the hydraulic limestones, from the most noted localities, published in the Geological Report of the State of New York, 1839, are given by Dr. Beck.

This stone belongs to the same bed which yields the hy

draulic cement obtained near Kingston, in Upper Canada.

Analysis of the Hydraulic Limestone from Ulster Co., along the line of the Delaware and Hudson Canal, before and after burning.

The hydraulic cement from this last locality has become generally well known, having been successfully used for most of the military and civil public works on the sea-board.

From the results of the analyses of all the above limestones, it appears that the proportions of lime and clay. contained in them place them under the head of hydraulic cements, according to the classification of M. Petot. They do not slake, and they all set rapidly under water.

47. The discovery of the hydraulic properties of certain magnesian limestones is of recent date, and is due to M. Vicat, who first drew attention to the subject. M. Vicat inclines to the opinion that magnesia alone, without the presence of some clay, will yield only a feeble hydraulic lime. He states, that he has never been able to obtain any other, from proceeding synthetically with common lime and magnesia; and that he knows of no well-authenticated instance in which any of the dolomites, either of the primitive or transition formations, have yielded a good hydraulic lime. The stones from these formations, he states, are devoid of

clay; being very pure crystalline carbonates, or else contain silex only in the state of fine sand. From M. Vicat's experiments it is rendered certain that carbonate of magnesia in combination with carbonate of lime, in proportion of 40 parts of the latter to from 30 to 40 of the former, will produce a feebly hydraulic lime, which does not appear to increase in hardness after it has once set; but that, with the same proportions, some hundredths of clay are requisite to give hydraulic energy to the compound. This proportion of clay M. Vicat supposes may cause the formation of triple hydrosilicates of lime, alumina, and magnesia, having all the characteristic properties of good hydraulic lime.

48. The hydraulic properties of the magnesian limestones of the United States were noticed by Professor W. B. Rogers, who, in his Report of the Geological Survey of Virginia, 1838, has given the following analyses of some of the stones from different localities.

The limestone No. 1 of the above table is from Sheppardstown on the Potomac, in Virginia; it is extensively manufactured for hydraulic cement. No. 2 is from the Natural Bridge, and banks of Cedar Creek, Virginia; it makes a good hydraulic cement. No. 3 is from New York, and is extensively burnt for cement. No. 4 is from Louisville, Kentucky; said to make a good cement.

49. M. Vicat states, that a magnesian limestone of France, containing the following constituents, lime 40 parts, magnesia 21, and silicia 21, yields a good hydraulic cement; and he gives the following analysis of a stone which gives a good hydraulic lime.