Mortar made of one part of fresh lime measured in paste 77 13 14 15 344 12 Mortar do. do. do. and two parts of com- Mortar made of one part of Obernai lime measured in 121 187 275* Mortar of one part of quick-lime but little burned, mea- -22 16 Mortar made of one part of Lixen lime measured in -22 17 Mortar of one part of same lime do. and two parts Observations on the experiments of Table No. XLII. This table contains a variety of experiments, which I will explain. Nos. 1, 2, 3 and 4 were made of lime slaked soon after being burned, and by the necessary quantity of water, reduced at once to paste. These hydrates of lime like the mortars which precede them, were placed in a cellar, and tested at the end of a year. The hydrate of Obernai lime, No. 1, was very good. No. 2, a hydrate of Verdt lime, gave so feeble a result as to surprise me, after that which I had obtained by placing a hydrate of the same lime in water-table No. III shows that the resistance of this hydrate was 484 lbs. As the specimens were from different burnings, I presume that in this last trial, I used a piece but feebly hydraulic. The Metz lime *This mortar being a little cracked, its resistance was diminished. 176 -22 132 176 No. 3, gave a feeble result, also. I have already said that I made but few experiments with this lime, and it is possible that the small quantity that was sent me was, by accident, but feebly hydraulic. No. 4 was from the Boulogne pebbles, and was treated the same way as the preceding. The resistance was feeble, and, we have seen (table No. VIII) that, with a single exception of a trial made with this lime highly calcined, all the mortars it has furnished, have supported but small weights. The above lime, No. 4, had received only the ordinary calcination. Nos. 5, 6, 7, 8, 9 and 10 were made of fat lime that had been lying slaked, and wet, for five years, since the erection of the Theatre. The proportions were one part of this lime in paste, to two parts of the several substances mentioned in the table. The mortar No. 5, composed of this lime and puzzolana, gave a very good result. No. 6 made, in the same manner, of trass, gave a resistance a little better still. Mortar No. 7 made of the hydraulic cement of Sufflenheim, gave a resistance equal to that afforded by puzzolana. Mortar No. 8 made of equal parts of lime, sand and Sufflenheim cement, supported a weight rather less than No. 7, in which there was no sand. No. 9 was made in the same manner as the preceding mortars, using the scoria of forges. I satisfied myself that these scoria contained little or no clay; and it is to this that I attribute the bad result. I said in the first section, that with the Tournay ashes, and the ashes of the forges of Boulogne, very good mortars were made; owing to this, that the sea-coal, burned in the forges of those places, contained a considerable quantity of clay, which was calcined in a current of air, by the combustion of the carbon of the coal. The scoria of forges, and the ashes of furnaces, should not, therefore, be used in mortars in the air, before ascertaining whether these matters have the property of causing lime to indurate under wa ter. No. 10 is a mortar composed of one part of fat lime measured in paste, one part of sand, and one of Paris cement. This cement was from the manufactory of Mr. Saint Leger, and was the same as that used for the mortars put into water. We saw, at page 83, that two mortars made of this cement had promptly hardened in water, but that both were cracked. The mortar made of one part lime and two parts of cement supported 187 lbs., and that made of lime, sand and cement, supported only 99 lbs. was much surprised at the bad result of the mortar No. 10 in table No. XLII; it had so little consistence that it crumbled easily between the fingers. I attribute the bad effect to the great quantity of lime that Mr. Saint Leger mixed with the clay, in making the cement. It might be that the cement was too much burned. Some separate trials lead me to think that cements made of clays containing about one tenth of lime, are less proper for mortars in the air than for mortars in water: it appears also that they allow but little sand in the composition of the mortar. I intended making some experiments to settle this matter but had not time. My departure from Strasburg also prevented my making, with the several clays of the environs of that place, experiments in the air, analogous to those which I made with the clays, under water. My various essays, however, induced me to think that in making artificial puzzolanas for mortars intended to be exposed to the air, the presence of lime in the clays to be calcined, is still more hurtful than when the mortars are to be used under water. Clay, therefore, should be chosen which contains no lime or very little. Nos. 11 and 12 were made of fat lime reduced to paste shortly after burning. No. 11 was made of one part of this lime measured in paste, and two parts of common sand. No. 12 differs only in having the sand pulverized. We see that the result was much better with the fine sand. Nos. 13 and 14 were similar experiments made of Obernai lime. With the fine sand, the resistance was, in this case also, much the greatest, although the mortar was so cracked as necessarily to diminish its force. We have seen in table No. XXIX, that mortars in water gave similar results. We ought to conclude, therefore, that whether for mortars in air or in water, fine sand is the best, notwithstanding the opinion to the contrary of most constructors. Old mortars are often found which are very hard, and which contain a great quantity of gravel as large as a pea. This fact is sometimes cited to prove that it is best to use coarse sand in gross masonry, but the reasoning is not just. These kinds of mortars are really concretes: the gravel they contain can have no influence on the goodness of the mortar. But if this gravel is mixed with fine sand (as is often the case) and the lime is hydraulic, then a very good mortar is obtained the strength of the mortar depending on the strength of the lime. No. 15 was made of lime which had been placed above the tiles in the kiln, and was, therefore, but slightly burnt: it was the same lime as was used in making the mortar to be put in water, No. of table No. XXIX. Only bad mortars were obtained by this means, either in the air or in water. Nos. 16, 17 and 18 were made of three different kinds of sand and a lime moderately hydraulic, obtained from the village of Lixen, near Phalsburg. No. 16 was made of one part of this lime, measured in paste, and two parts of a very earthy pit sand, which is found in the neighbourhood. The resulting mortar had so little consistency, that it could not bear the weight of the scale pan. No. 17 was mixed in the same proportions with river sand from Zorn, near Saverne; the resistance was passable. The same proportions were observed, in mixing No. 18, with the same sand as was used in No. 16, after being freed, by washing, from earthy matter. We see that this mortar was good, and superior to the mortar made of river sand. Nos. 19, 20 and 21 were repetitions of three preceding experiments: using, however, another lime, also moderately bydraulic, obtained from the village of Dosenheim. The mortars made of Dosenheim lime, like those made of Lixen lime, prove that earthy sands afford only very bad mortars; but that, being washed, they are superior to river sands. I was led, in 1823, to make these experiments, because there was to be had near Phalsburg only pit sand which was half earth. Whenever there was any work to be executed requiring some care, the people of that place were obliged to get river sand from the river Zorn on the other sides of the Vosges. This brought the price to about $0.03 per cubic foot--so high as to prevent its being procured for the masonry of revetments: it resulted that the masonry of that place, made of mortar in which the earthy sand of the neighbourhood was used, has needed considerable repairs, and in making the necessary reconstructions, it was very apparent that the degradations had been owing to the bad quality of the mortar. After getting the results of these last experiments, I used no sand at Phalsburg except washed pit sand. It required 70.68 cubic feet of the earthy sand to yield 35.34 cubic feet of the washed sand: 0.62 of a day's work sufficed for the washing: it would, therefore cost less than one half of the expense of bringing the river sand. The sand may be washed on a large scale in the following manner; a basin being made of masonry from seven to ten feet wide, and from twelve to sixteen long, the height of the walls should be about two and a half feet, with the exception of one end, which should be only one foot two inches high; the bottom should be paved with flat stones; the basin should be built near a stream of water, or if that be not practicable, a well should be sunk near it. A layer of sand of about one foot thick, should be placed in the basin, and a plank one foot four inches wide placed on edge, on the low wall, raising it to the height of the other walls-the plank being fitted into grooves made in the side walls to receive it. The basin must then be filled with water from a brook, or from a pump in a well, as the case may be; and the sand must be well stirred up with rabs by two or three labourers. Allowing the time found to be necessary for the sand to precipitate, the plank must be suddenly withdrawn, and a great part of the water will pass off at once, loaded with earthy matter. This operation must be repeated until the water passes off but slightly turbid: the sand may then be taken out and left to dry, and the washing be applied to another portion. For economy, the basin may be constructed of planks, as was done at Phalsburg. It was six feet eight inches long, four feet four inches broad, and two feet two inches deep. There was left in front an opening of only fourteen inches deep by ten inches broad. But this opening was too small for the water to run off rapidly. It is best to place a movable plank of some breadth across the whole front of the basin, so that the water may pass off very quickly. The last experiments of table No. XLII, show how important it is to use clean sands in making mortars: but before washing off the earthy matter, it is proper to be satisfied, by the means I have pointed out, that the sands are not arenes. CHAPTER XIV. Observations on Mortars exposed to the Air. It results from the experiments given in chapters XI, XII, and XIII, that in exposing to the air mortars made of sand, and lime which had been laying a long time slaked and wet, I obtained no satisfactory result; while I obtained tolerable results with sand, and the same lime recently slaked. The resistances of these last mortars were 68, 77, and 99 lbs., while the others were unable to support the scale pan, whatever may have been the process of fabrication. I ought not, however, from this to take up a general conclusion, and counsel against slaking and running lime into vats to preserve it; because I have not made experiments enough to pronounce positively on the subject-which is one of great importance. It is necessary to repeat these trials in different countries, so as to operate on various kinds of lime, before proscribing this method; which, while it may be a bad method for certain kinds of lime, may be very good for other kinds. I do not know for how long a time the method of running lime into vats has been followed. It may have been introduced in consequence of the considerable increase of bulk which it gives. I do not know that it was followed by the ancients. Vitruvius has left a work on architecture, in which he has given many details as to the manner the Romans carried on their works. We find in this author, as rendered from the Latin by Perrault, the architect, the follow ing passage extracted from Book II, chapter V: "When the lime has been slaked, it must be mixed with sand, in such proportions that there shall be three parts of pit sand, or two parts of river sand to one of lime: because this is the most just proportion of the mixture, which will be much better still, if there be added to the sea or river sand a third part of sifted tile dust." We see nothing in this passage that indicates the mode of slaking; but it is certain that the Romans made great use of hydraulic lime, as there are many remains of their works in countries where this lime abounds: such are the constructions they have left us on the banks of the Moselle, and in several parts of France. But these limes could not be slaked and left in the above manner, (as they would harden in the water;) and, if it had been the practice to slake them differently from fat lime, Vitruvius would no doubt have mentioned it. It appears probable to me, therefore, that the Romans used fat lime as they did hydraulic lime, that is to say, immediately after the burning. This is the more likely, as Vitruvius directs, in the process of stucco making, that only lime that had been long slaked should be used. The following are his remarks on this subject. Book VII, chapter II. "Having examined all that appertains to pavements, the manner of making stucco must be explained. The principal matter in this is, that the lime should be slaked for a long time, so that if there should be some particles less burned than the rest, they may, having time thus given them, be as thoroughly slaked, and as easily tempered, that which was thoroughly calcined: for, in lime which is used as it comes from the kiln, and before it is sufficiently slaked, there is a quantity of minute stones imperfectly burned, which act on the plaster like blisters, because these particles slaking more slowly than the rest of the lime, break the plaster and mar all the polish." It appears to me that the precaution of slaking the lime a long time before hand, is here recommended as an exception, and that in the mortars intended for masonry, the Romans used all limes soon after they left the kiln. It is remarkable that the same author directs, in the first passage cited, mixing with the mortar a portion of sifted tile dust, observing that it will much improve the mortar. as We have seen that my experiments were very unfavorable to the process indicated by Mr. Loriot and Mr. Lafaye: they were in error in recommending them as, in principle, recovered from the Romans. Moreover, these processes have, for a long time, justly fallen into disrepute. As to the opinion that the hardness of mortar is due to the regeneration of carbonic acid, I have shown that according to the analysis of Mr. Darcet and Dr. John, several ancient mortars, although very hard, contained but a small portion of the carbonic acid necessary to the saturation of the lime. It has been stated that the Italians sell little caskets and snuff boxes which they make of ancient Roman mortars: but it has been noticed that they use for these purposes only the exterior parts of the mortar in which the lime had passed to the state of carbonate, while the interior often afforded but a weak consistence. In examining Roman mortars, it is observed that they are often of great hardness, although it is evident that the mixture had been made with very little care. We must therefore attribute the hardness of these ancient mortars to other causes; for, as I have said, all these mortars are not by many degrees equally hard. To explain the hardness of Roman mortars, it will suffice, I think, to cast the eyes over tables Nos. XXXVI, XL, XLI, and XLII. Table No. XXXVI contains mortars made of hydraulic lime and sand. These mortars |