same clay mixed with 0.02 of lime, hardened in seventeen days, and broke under a weight of 352 lbs. The mortar made of the natural clay that had been heated for six hours in a current of air, hardened in five days; but it broke under a weight of 330 lbs. Lastly, the mortar made of the clay which contained 0.02 of lime, and which was, also, heated for the same time in a current of air, hardened in three days; but this mortar was cracked, and broke under a weight of 198 lbs. These experiments were made in the beginning of 1825. Having communicated these results to Mr. Bergère, chef de bataillon, of the engineers, he informed me that Mr. Raucourt, engineer of roads and bridges, had published at Petersburg, in 1822, a memoir in which he mentioned the influence of air on the calcination of clays that are to be transformed into puzzalonas. I procured this work, and quote the following remarks from page 130. "I had thought for a long time that the degree of calcination could not be the only cause of the superior qualities that argillaceous earths acquire by a few minutes' torrefaction: if it were otherwise, slightly burned bricks would furnish excellent puzzalonas, which is far from being the case, and several essays made with pounded bricks, burnt with various degrees of intensity, gave me no result comparable to that given by clay exposed on a red hot plate. "It was thence inferred that the contact of air is necessary to modify, in the most favorable manner, the oxides which the earths contain, so that they may form good hydraulic combinations with lime. To assure myself more completely, I made direct experiments which fully confirmed this induction, and which led me to more particular researches than had before been made on factitious hydraulic lime." The experiments of table No. XVI show, in opposition to the opinion of Mr. Raucourt, that lightly burned bricks may furnish very good puzzalonas, when they contain lime, and the burning has been properly managed. This engineer asserts positively, in this quotation, the necessity of contact of air to modify the clays advantageously; but he reports none of the experiments that he announces as having made. At page 135 of his memoir he says: "If it be true, as is said, that the earths are metallic oxides, one might be led to think that they have need of a certain degree of burning in contact with the air, to form with lime, and the concurrence of water, insoluble compounds; and as several chemists have already shown that the presence of silex in the state of gelly will contribute to render a fat lime hydraulic, that it is the same with the oxides of iron and magnesia; that Mr. Vicat, by his transformations with clay, proves that alumine, also, might enjoy this property; that if the very hydraulic lime I H (Art. 163) be observed, it will be allowed that magnesia must necessarily fulfil analogous functions; one would be almost convinced that all the metallic oxides, properly prepared with fire, would form, with lime, combinations susceptible of hardening in water.' There are many errors in this passage; for it is demonstrated that iron and manganese act no part in hydraulic limes; and what Mr. Raucourt says in this particular, proves that he has not consulted experience. Nothing has proved, as yet, that alumine, or magnesia, possesses the property of forming hydraulic lime. (The lime cited art. 163, contains clay.) Lastly, nothing is more doubtful than such properties as Mr. Raucourt has attributed to almost all metallic oxides. In a matter so delicate as this, the imagination must not get in advance of facts. As Mr. Raucourt has not given the experiments which led him to the opinion that the air acts an important part in perfecting artificial puzzalonas, I am obliged to draw my conclusions from the facts presented in my preceding table, and principally from the last four experiments reported in page 85, There are two things to consider in artificial puzzalona; the first, is the promptitude of induration of the mortars whereof they form part; the second, is the resistance of these mortars. The experiments at the end of table No. XX, the observations I made on Nos. 5 and 6, of table No. XXIV, and the few experiments cited in page 85, prove that when these clays are calcined in a current of air, they harden much the more promptly. But is the resistance of the mortars greater, also? I cannot affirm positively that it is. We see, for example, in the four experiments cited, that the case of the most prompt hardening, coincides with the weakest resistance; but we ought not to conclude from thence, in a positive manner, that the calcination in a current of air diminishes the resistance at the same time that it increases the promptitude to harden; because the result obtained may have depended on some other cause-as, for instance, the degree of calcination. What induces me to think that calcination of clays in a current of air, far from diminishing the resistance of mortars, will, on the contrary, augment it, is, that all the clays Nos. 5 and 6, of table No. XXIV, having been heated in this manner, the hardening was very prompt, at the same time that the resistances were very great. I cannot positively affirm that this last effect will follow, but I think it probable. I have not had time to make the direct experiments that I intended, in order to clear up this point. In a note printed by me in 1825, I stated that I was induced to think that at an elevated temperature, the alumine contained in clays absorbed oxygen, and that this absorption rendered cements more proper to combine with fat lime in the moist way. Mr. Vicat is of a different opinion. He inserted a note in the Annales de Chimie, of 1827, Vol. XXXIV, wherein he says that he calcined, for half an hour, pulverised clay in close vessels, and that he heated the same quantity, during five minutes, on a metallic plate kept at a common red heat. After cooling, the substances were weighed, and were found to weigh nearly the same. Mr. Vicat concludes from the small differences found between the weights of clays calcined in close vessels, and those calcined in the air, that there is, incontestably, no absorption. I will remark, that nothing can be concluded from this experiment. A part of the clay was calcined during half an hour, and the other part during five minutes only; the quantities of water lost by these two portions could not, therefore, have been the same, since they were not equally heated. It is, besides, possible that a small quantity of oxygen, difficult to appreciate with a balance; might suffice to give new properties to the clay. To know whether alumine absorbs oxygen, it would be necessary to heat it highly in a tube not susceptible of oxidation, and to pass, during the calcination, at different times, a given volume of oxygen gas, over the incandescent alumine, and, afterward, to measure the volume of gas, in order to ascertain whether it had been diminished. I had not under my control the means necessary for making this experiment; the observation that I made, that alumine calcined in a current of air, dissolved more easily in sulphuric acid than when calcined in a close vessel, led me to think there was an absorption of oxygen, but it is no proof; I offer it as a presumption only. Several Engineers have proclaimed the good results obtained with ashes derived from the combustion of coal in furnaces, or lime kilns; others on the contrary, have denied the effect of this substance. With this question, it is the same, I am satisfied, as with the question whether dust of tiles or bricks, much, or little burned, should be taken. The good results of the Tournay ashes* have been known for a long time, and are contested by no one. Having been employed at Lille, in 1815 and 1816, I had an opportunity of knowing the good effects. But when I wished to use, in the same way, the coal ashes at Strasburg, I could not obtain a good result. I made mortars composed of one part of fat lime measured in paste, and two parts of coal ashes: after an immersion of a year, these mortars were as soft as if made of sand. These opposite effects surprised me, and on examining different coals and their analyses, I saw that several of them contained quite a quantity of clay, while others contained little or none. But coals are generally burned on a grate: the clay they contain is thus calcined in a current of air; and it is the mixture of this clay with a little iron, constituting the residue, that is used, when we take these ashes: we see, therefore, that it is a real puzzalona that they have been making, for a long time, without knowing it. Should the coal contain no clay, or should the clay be mixed with too much lime; in the first case no result will be got; and in the second, if the calcination has been too high, the ashes will possess but an indifferent quality. I think Mr. Sganzin is wrong when he says in his cours de construction, page 32, "Experience teaches that the ashes of all coals which have served for the calcination of lime, will form a mortar hardening promptly in water." We know that when lime is calcined with coal, the ashes of the combustible is mixed with a considerable quantity of particles of lime. Although the coal should contain no clay, if the lime calcined be very hydraulic, I conceive that a mortar of fat lime and these ashes would harden in water; but the result would be due to the presence of the hydraulic lime; I think that no result would be obtained if, with such coal, the calcination were of fat lime. In 1826, I was charged with the inspection of several places along the Straits of Calais. Much coal is used in these departments. At Boulogne where the forts of the sea coast were to be repaired, I requested Capt. Le Marchand of the Engineers, to make some experiments with_cements and the coal ashes of the neighbourhood, because the use of the Boulogne pebbles, before mentioned, was very expensive, and it was difficult to obtain them in quantity. This Engineer took great pains in his researches, and informed me that he had obtained good results with some cements, and especially with the ashes got from the coal burned in several manufactures in Boulogne. He procured the analysis of this coal, which is composed of the following substances; combustible matter, 96.62; alumine, 2.00; silex and iron, 1.38. Therefore the ashes he used were nothing else than a very aluminous clay, which contained no lime, and which had been calcined in a current of air during the combustion of the coal, and it is not astonishing that it gave very good mortar. The cinders of forges, another residue of the combustion of coal, may be assimilated to ashes: there are some that give very good, and others that yield no results: neither should, in any case, *Rondelet, in his art de batie thus describes this substance. "This powder is made of half burned fragments of a very hard blue lime-stone. These fragments fall, during the burning, through the grate of the lime kilns, and are mixed with the ashes of the coal. The Tournay ashes are considered equal to the Dutch trass, and are used for the same purposes." TR. be employed without our being assured of their quality. To know if they may be used with advantage, the practical process for distinguishing good cements from those that have no hydraulic property, that I will soon point out, should be followed. I commenced my experiments on artificial puzzalonas in 1821; and the first operation I performed was to see whether I could make puzzalona and trass anew out of their constituents. I accordingly took the substances contained in trass and puzzalona, according to the old analysis which is given in p. 53; with these I made a paste with water; afterward, I calcined the mixture at a low red heat for six hours; and, lastly, reduced it to very fine powder. As I had no natural alumine at my command, and as I doubted the efficacy of that to be obtained from the decomposition of alum, I took the Cologne pipe clay, washed it several times with a great deal of water, and decanted, to separate the greater part of the sand from the alumine. I assured myself, by calcining a small portion of this earth, and dissolving it in sulphuric acid, that it contained hardly any silex. This is the substance to which I added the other matters in the proportions given in the old analysis. We see then that, by this operation, my artificial trass and puzzalona had a little more silex than the natural productions, by the quantity retained in the aluminous earth; but this augmentation of silex was the same for both mixtures. I made two mortars by taking one part of Obernai lime, and two parts of each of these compounds: the mortar of the factitious trass hardened in four days, and broke under the weight of 385 lbs: that made of the artificial puzzalona hardened in three days and supported 477 lbs. before breaking. The lime was the same in both experiments: all other circumstances were alike: wherefore we must attribute the superiority of the artificial puzzalona over the artificial trass, to the clay of the first mixture containing much more alumine than the second. I was wrong in using hydraulic lime: I should have used fat lime, which I, afterward, always used when I wished to determine the quality of puzzalonas or other analagous substances. This experiment, and those which were made of the very aluminous clays of Frankfort and Cologne, prove that results, exactly like those furnished by natural puzzalona, are obtained, by suitably calcining greasy clays. I was not able to determine the proportion in which the silex and alumine should exist to give the best results; but I am led to think that the alumine should equal, at least, a third of the silex. We have seen, however, that the Sufflenheim clay, which contains seven parts of silex to one of alumine, sometimes produced very good cements; but it is probable the best were obtained with portions of clays more aluminous than the others. The results contained in table No. XXII support this opinion. It is true we might be inclined to infer the contrary from the new analysis of trass and puzzalona made by Mr. Berthier, and given in p. 53. The proportion of alumine is about the same in Trass and Puzzalona, according to Mr. Berthier, and is much smaller than according to the older analysis: but the analysis of a single specimen must not fix the proportions of a substance which gives, as we have seen, very various results; and every thing leads to the belief that the several pieces of trass and puzzalona vary much in their composition. It is possible that the specimens of trass and puzzalona that I sent to Mr. Berthier, were possessed of a high degree of energy, although containing but little alumine, by reason of the potash they contained; for this substance augments, in a sensible manner, the energy of puzzalonas, as we have seen in the experiments of table No. XXIII. "But the good results obtained from the calcination of greasy clays, prove that cements without potash, may be made to be quite equal to trass and puzzalona. The experiments above show that, with artificial puzzalona and fat lime I have obtained mortars much superior to those made with artificial, or even natural, hydraulic lime, and sand. Although I happened, with some pieces of Obernai lime, to obtain results approaching those afforded by artificial puzzalona, such instances are rare; and, in cases like these, it is the general bearing of the facts that we are to regard. I announced these results in a little pamphlet published in 1824, and I stated, moreover, that there would accrue a sensible economy. Mr. Vicat, in a criticism on this pamphlet has endeavoured to prove the contrary; but it will not be difficult to show that he was deceived in his calculations. This Engineer says "The objection of Mr. Treussart to the high price of artificial limes is without foundation. In fact the trass mortars are as follows: For two cubic metres of trass (70.68 cub. feet) a $5.221 $10.45 2.28 $12.73 "The three cubic metres of materials are reduced by the mixture to 2.30m; it follows that the cubic metre costs $5.53 (35.34 cub. ft. cost $5.53 equal $0.16 per cub. foot.) On the other hand to make a cubic metre of hydraulic lime mortar, requires 0.90m of common sand a $0.281 0.43m of hydraulic lime in stiff paste, which at the mean price will cost (one foot cost $0.34) $0.26 5.27 $5.53 The prices then will be exactly the same, since in each case it is found to be $5.53: but let us see if the basis of this calculation is exact. I will first remark, what I did not neglect to state in my pamphlet of 1824, namely that the mortars of fat lime, sand and trass, gave me results which were often superior to those in which there was trass without sand; and that it was the same with mortars made of puzzalona. We may satisfy ourselves by table No. XIII that when the mortars of trass and puzzalona, alone, were superior to those containing sand, the advantage was not suf ficient to lead to a preference of the former. I obtained a like result with artificial puzzalona of table No. XXIV. It is, therefore, an error of Mr. Vicat's to compare the price of mortars made of artificial hydraulic lime, with that made of fat lime and trass without sand: it is necessary to compare it with mortar made of lime, sand and trass. If the first calculation, above, be thus rectified, the price of $10.45, given by two cubic metres of trass at $5.221, will be reduced to $5.51, resulting from one cub. metre of sand at $0.28, and one cub. metre of trass at $5.223: consequently the cubic metre of mortar composed of fat lime, sand and trass, will amount to $3.39 $0.10 per cub. foot, only, instead of $5.53. The objection that I made, therefore, is not, as Mr. Vicat thought, without foundation. I feel bound to state that the prices I have given, using the data established by Mr. Vicat, appear to me to be too low for the principal places in France; but I was obliged to use the elements he had employed. It is possible that in countries where chalk is abundant it will not cost more to make hydraulic mortar with artificial hydraulic lime and sand, |