Lime produced by different calcined limestones, yielding common lime according to the analysis of Mr. Berthier. 0.964 0.954 0.972 0.935 0.916 0.860 0.780 0.600 0.015 0.200 0.262 0.020 0.000 0.138 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1. Limestone of the fresh water formation of Chateau-Landon near Nemours; compact, yellowish, a little cellular, sonorous; yields very fat lime. 2. Limestone of Saint-Jaques; compact, yellow, texture somewhat saccharoidal; it forms the base of the Jura mountains; makes a very greasy lime which hardens but slowly. 3. Lower marine limestone (calcaire grossier) of Paris: gives very greasy lime. 4. Limestone which forms the roof of the iron miue of La Voulte (Ardiche;) compact, yellowish white: containing shells which prove it to be contemporaneous with the Jura limestone, specific gravity 2.67: gives very good fat lime. 5. Limestone of Lagneux (Ain:) compact, of a light yellowish gray; affording fat lime which is much used at Lyons. 6. Fresh water limestone of Vichey (Allier:) compact, cellular, yellowish white, gives very good lime, but not very greasy. 7. Limestone of the neighbourhood of Paris, which appears to belong to the fresh water formation: compact, yellowish; gives meagre lime, but not hydraulic. 8. Secondary limestone of Villefranche (Aveyron:) lameller, of an ochery colour, the lime obtained in an experiment on a small scale was very meagre without being hydraulic. Limes produced by different limestones, yielding hydraulic lime according to the analysis of Mr. Berthier. 0.870 0.830 0.840 0.820 0.820 0.745 0.688 0.7400.683 0.700 0.746 10.040 0.025 0.015 0.015 0.035 0.060 0.020 0.020 0.010 0.160 0.090 0.070 0.1350.1650.165 0.2200.252 0.1700.240 0.290 0.078 0.100 0.070 0.057 0.016 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1. Limestone of Vougny (Loire;) sub lamellar, yellowish, filled with ammonites and other shells; yields very good lime which sets in water. 2. Limestone of Saint-Germain (Ain;) compact, deep gray, veined with white carbonate of lime; lamellar, and penetrated with gryphites, &c., at Lyons this lime is used for hydraulic works. 3. Limestone of Chaunay near Macon; compact, fine grained, yellowish white, it is of the secondary formation: this lime is hydraulic. 4. Limestone of Digne (Jura;) compact, penetrated with plates of calcspar (lamelleo de calcaire) and containing a great number of gryphites, of a deep gray, this lime is hydraulic. 4. Limestone which accompanies the preceding, and which possesses the same properties; compact, of a grain almost earthy; of a clear gray. 6. Secondary limestone of Nimes (Gard;) compact, yellowish gray; affords a hydraulic lime which is there considered of excellent quality. 7. Lezoux lime (Puy-de-Dome;) made of a fresh water calcareous marle; it is said to be excellent, they are in the habit of slaking it by leaving it in heaps in the air, after having moistened it: it produces a copious jelly with acids. 8. Compact limestone of an unknown locality: gives very good hydraulic lime. 9. Secondary limestone of Metz (Moselle;) compact, of a grain almost earthy, of a bluish gray more or less deep: the lime it affords is known to be very hydraulic. 10. Calcareous marle of Senonches, near Dreux (Eure-et-Loir;) compact very tender, may be diffused through water like clay, but does not fall to powder when burnt. This substance is not like the limestones which have an earthy fracture, a mixture of carbonate of lime and clay. It leaves in acids a mealy residue, soft to the touch, which contains only a trace of alumine, which dissolves in liquid caustic potash even when cold, and which comports itself in all respects like silex which has been separated from combination: nevertheless it is certain that this substance exists in the Senonches lime only in the state of mixture: because, by operating with great care, we find by analysis, that the proportion of carbonic acid is exactly that which is necessary to saturate the lime. I have, before, in some varieties of carbonate of magnesia (magnésie carbonatée,) encountered silex soluble in alkalis, although not in combination, but have never found it in carbonate of lime. The Senonches lime is very well known: it is much used at Paris: it hardens more promptly, and acquires greater hardness than Metz lime: it dissolves in acids without leaving the least residue. (What Mr. Berthier says here of this lime is very remarkable and deserves to fix attention on this particular kind of lime.) 11. A mixture of four parts of chalk from Meudon and one part of Passy clay (in volume,) which Mr. Saint-Leger uses to make the artificial hydraulic lime of Paris. If we compare the common limes of the first table, above, with the hydraulic limes of the second, we shall see, 1st. that the latter contains, in general, much more clay than the former: 2d., that several limes contain more than two-tenths of magnesia, without being hydraulic, while they become eminently so, when they contain the same quantity of clay: 3d., that almost all the common limes contain a small portion of clay. We see that No. 5 of the common limes contains, within one thousandth as much clay as No. 2, of limes moderately hydraulic: it is probable that these two limes have about the same degree of hydraulic property, but that it is weak. It would be interesting to know the resistance of the mortars made of all the limes contained in the above two tables. It is only by determining the tenacity of mortars made of limes of which the composition is well known that we can adjust the composition and proportion of clay so as to produce the best hydraulic limes. CHAPTER VIII. Of Sand, and Hydraulic Sand (Arénes.) Sands are classed relatively to their constituent parts: thus there are siliceous sands, granitic, calcareous sands, &c., some sands result from the slow decomposition of rocks of the same nature. Sometimes they are mixed; and it often happens that they contain several metallic substances-principally iron. The different revolutions that the earth has undergone have caused considerable deposits of sand in places where there are now no water courses; and even at great elevations. On certain coasts there are extensive collections of sand, which the French calls dunes; these are heaped up by the winds. Rivers transport a great deal of sand, and their shores are some times covered with it. Sands are often mixed with vegetable earth. In this case they are not proper for mortar. To be suitable to this end, they should be almost perfectly free from earthy matter. When on the subject of mortars exposed in the air, I shall point out a very simple means, that I have used for several years, of freeing sands from the earth they contain. Constructors distinguish sands into river-sand, sea-sand and pit-sand. This last is found in the great deposits mentioned above: it bears the name of fossil sand, also: its grain is generally more angular than that of sea sand or river sand. All these sands contain the same elements. Siliceous, or granitic sand, or a mixture of the two, are most common: calcareous sands are most rare. Vitruvius, and others after him, thought that fossil or pit sand was the best for making mortar. Belidor thought, on the contrary, that river sand was preferable. Mr. Rondelet has since made experiments which appear to establish that pit sand is better than river sand. I purposed examining whether, in fact, there was much difference, in making mortars of one sand rather than of another: but I quitted Strasburg before I could apply myself to the subject. Nevertheless, some facts, of which I shall speak when on the subject of mortars exposed to the air, lead me to believe that the divergence of opinions, as to which are the best sands, results from the experiments having been made with sand more or less fine, or more or less earthy. The experiments cited page 105, show that earth mixed with sand is very injurious to mortars. But the authors quoted above do not say whether, before making these experiments with pit and river sand, they took care to wash both of them. If they did not wash them, the superiority which they found to belong to either, may have been, on one hand, due to the greater freedom from earthy matters of the better sand of the two, and on the other, to the greater fineness of the particles. My results were obtained with granite sand, and it remains to be ascertained whether they would have been the same with other kinds of sand. The question is important, and should be examined with care A species of fossil sand has lately been discovered, which is very remarkable: the knowledge of this singular substance is due to Mr. Girard de Caudemberg, Engineer of Roads and Bridges. This Engineer published, in 1827, a very interesting notice of this subject, which cannot fail to produce important results. I will state succinctly the principal facts con tained in this notice, and I will add some observations that have been made since. "There exists" says Mr. Girard," in the valley of the river Isle, fossil sands of which the colour varies from redish brown to yellowish red and even ochre yellow. They are called •arénes,* which denomination we shall preserve in this notice, to distinguish them from common sands. These sands are often used alone, as mortar, in walls of enclosures and of houses; and as they have the property of making a paste with water, and as they shrink less than clay, they are very proper for this kind of construction: they represent in this case a pisé, which acquires hardness and resists inclemencies. But the proprietors of the mills on the river Isle, in the department Gironde, discovered by accident a quality in the arenes much more important and worthy of serious attention; they use it with common lime more or less fat, to form mortars which set under water and acquire great hardness." Mr. Girard says that for want of hydraulic lime, he made several Locks with mortar composed of common lime and arenes. He states that he obtained very good results; and that the following year it was necessary to use the pick to break up the concrete that had been made with these arenes. The examination of the arenes showed Mr. Girard that they were all composed of sand and clay in various proportions. By means of washing and decantation he separated the clay from the sand, and in eight kinds of arenes he found the proportions of clay varied from ten to seventy per cent. He ascertained that those arenes which were meagre, were hydraulic only in a very feeble degree. The sand of the arenes is sometimes coarse and sometimes fine: it is occasionally calcareous, but more frequently siliceous or mixed. Some of the arenes are red, others brown, yellow and sometimes white. The arenes are generally found on the summit of the hillocks which form the basins of rivers and brooks: they are rarely found in valleys. The deposits of the substance are superimposed on masses of argillaceous tufa (tuf argileux,) or calcareous rocks; they have all the characters of an alluvial deposit. The beds are often separated by pebbles. Rolled pebbles are, moreover, often seen disseminated here and there in the mass. Some of the beds are more than fifty feet thick. Mr. Girard says it appears to him that the environs of Bordeaux, and the valleys of the Aube and upper Seine, contain a great deal of it; and that it exists in a multitude of localities. Mr. Girard had occasion to ascertain that the arenes were employed in many ancient constructions, and he cites, among others, the thick revetments of a remnant of fortification at Mucidan (Dordogne) which dates back several centuries, and it appears that the very old constructions at Nimes were made with arenes. Mr. Girard says he has assured himself by experiments that in preserving for a year under water, mortars containing equal proportions of crude energetic arenes, and the same arenes calcined, that there was no appreciable difference in their consistence; but that the torrefaction of the arenes had the advantage of hastening in a remarkable manner, the setting or induration of the concrete. * It appears that the word arène was known to several Constructors, for Mr. Sganzin says page 25, in speaking of Sands: "They call arènes those of which the particles are finer and more regular." And this is all he says. Au. Mr. Avril and Mr. Payen discovered, about the same time, in Bretagne,the properties of puzzalona, in gray wacke, and in decomposed granite, though to a degree quite feeble. They remarked, besides, that natural puzzalonas acquire a new degree of energy by a slight calcination. Captain Leblanc of the Engineers, employed at Peronne, gave on the 30th November 1827, an interesting memoir on the arenes which are found in great quantity in the neighbourhood of that place. I will transcribe the commencement of the memoir. "In the numerous demolitions, made in 1825 and more especially in 1826, preparatory to the repair of the crown work of Paris, it was remarked that the ancient mortars (from 150 to 600 years old) were generally very hard. It was particularly noticed, at the time of the demolition of the piers of bridge forty-one, which was situated in quick sand, below the level of the waters, that the mortar was harder than elsewhere. To these facts the only exception was in the demolition of scarp thirty-three at the close of the year 1826. The mortar of this masonry was still soft. On examining the mortars which were hard, it was perceived that the sand therein was very fine, and that these mortars, from their aspect, seemed to have been made of the sand of the country, rejected in the official instructions, because too earthy. (This sand is used in all the constructions of the town.) Another consideration led to the belief that the sand of the country had been used: for all this masonry appeared to be very carelessly put together; the mortar, badly made, showed every where, lumps as large as a hazle nut, of lime not mixed with sand and still soft; although all the surrounding mortar was very hard. It was to be presumed that when applying so little care to all parts of the workmanship, the constructors had taken no greater, as to the choice of sand: and that they used that which was nearest at hand-namely the sand of the country. We have said that the mortar of scarp thirty-three was found still soft after two hundred years: it seemed on examination to be meagre; and, although the sand seemed to be the sand of the country, the mortar did not look like the other; under these circumstances, this example suspended, for the time, the conclusions that had already been drawn as to the advantage of using the Peronne sands." The author states that on recommencing labours in 1827, he made six cubes of mortar, of which three were composed of sand recommended in official instructions, and the other three of the clayey sand whereof the good masonry appeared to have been made. One cube of each kind of mortar was left in the air, one put in a humid place, and one in water. It was in this interval, as Capt. LeBlanc states, that the notice of Mr. Girard appeared. What was said in that notice showed that the clayey sand of the neighbourhood of Peronne was a true arene. The mortar made of common lime and this arene had completely hardened in the water at the expiration of a month; so as to receive no impression when borne upon strongly by the thumb. A mortar made at the same time of the same lime and of the sand recommended officially, and usually employed, remained entirely soft at the end of several months. By heating the arenes, Capt. LeBlanc ascertained that the hardening took place much more promptly, for the mortars made of the crude arenes required a month to harden, whereas those made of arenes that had been heated, hardened in eight or ten days. This officer undertook some experiments to determine the degree of calcination proper to impart the quality of most prompt hardening, and to ascertain whether the effect of calcination would be to augment in a |