Observations on the experiments of Table No. XXXI.

All the above mortars were composed of the same old lime as those of the preceding table. The experiments were made in duplicate: those in the first column were prepared in August, 1823, and were left during a year in the air, in a cellar; those of the second column were made in the month of October, 1824, and were left during a year in the air in a chamber where there was no fire. We see that the results are very different: 1st, the five mortars in the first column made of lime and trass only, gave much weaker resistances than the similar mortars in the second column, while it is the inverse with mortars made of lime, sand and trass: 2d, in the first column, the mortars made of lime, sand and trass, gave, in general, better results than the corresponding mortars made of lime and trass only, while it is the inverse in the experiments of the second column.

I am unable to account for the differences shown by these two series of experiments; I cannot say whether, or in what degree, it is to be attributed to their being made at different seasons, and placed in different atmospheres. It is not easy to ascribe such great variations to these two causes; I should rather be inclined to believe that the trass which I used in 1824 was not the same as that used in 1823, and that this has occasioned these opposite results. I purposed repeating these experiments, but my departure from Strasburg in 1825 prevented.

The mortars of the first column of table No. XXXI; were made at the same time as those of table No. XXX; and when, in 1824, I made the experiments of the second column, I also made five mortars like those of No. XXX. and placed them in a chamber--the preceding having been deposited in a cellar. These five mortars, composed of old lime and sand only, remained, like the analogous mortars, without consistence, and were unable to bear any weight.

Seeing that I could get no results with the old moist lime and sand, I made some essays agreeably to the process of Mr. Loriot; they are given in the following table.

Observations on the experiments of Table No. XXXII.

The process of Mr. Loriot consists in mixing a certain quantity of quick lime reduced to powder, with lime which has been lying for some time

4-52

0

slaked and wet; and following his method, I varied the quantities of the two kinds of lime, and yet we see, that I obtained no results. The mortar dries quickly, it is true, on account of the presence of the quick lime, but this is not a true induration. The property of drying quickly is what, no doubt, led Mr. Loriot into error. We see, then, that this mode, offered by the author as yielding very good mortars, gives, in fact, only very bad. It is not surprising, after seeing the above results, that the attempt to repoint the platform of the observatory by this method did not succeed.

Having no good results with the old lime, nor with Mr. Loriot's process, I quitted the erroneous methods of others, and made the following exper

iments.

Fat lime slaked in thick

1

lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs. lbs.

2333 99 50 44 33 33 33 33 33 22 22 22 22 22 22

143319 308 308 297 319 308 319 308 319 352 363 341 319|308

14

Observations on the experiments of Table No. XXXIII. These experiments were made at the same time as those of table No. XV, of the first section, and with the same fat lime. I slaked a part as it came from the kiln, giving it only the quantity of water necessary to reduce it to thick paste, and I made therewith the experiments comprised under Nos. 1 and 2. I slaked a part into thin paste, and made with it the experiments under Nos. 3 and 4, and I also slaked a part into dry powder, by giving it a quarter of its volume of water, and with this I made the two series, Nos. 5 and 6. All these experiments comprise the interval of a year, and the several epochs at which they were respectively made are given in the table. The figures of the table give the number of pounds that the mortars supported before breaking.

The series of mortar No. 1, is composed of one part fat lime slaked to thick paste, and two parts and a half of sand. We see that the mortar made immediately, acquired a hardness which is not, in fact, very great, but which is passable. The mortars made after fifteen days had nearly one

half less consistency; at the end of two months it had two thirds less, and the mortars made after six months had not strength enough to support the weight of the scale pan, &c., which was twenty-two pounds. This result is very remarkable. If we compare it with table No. XXX, of which the mortars being made of lime that had been lying slaked and wet for five years, had no strength, we cannot but think that slaking fat lime into vats and letting it lie there in a wet state, is a mistaken practice. The practice may have been induced from the considerable increase of bulk it gives to fat lime; but the trials I have made show it to be a very bad process, at least with the limes I used.

The series of mortar No. 2, was made of one part of lime in paste, to two and a half parts of sand and trass in equal proportion. The result was very good. It will be noticed that it was best after the 8th, 9th and 10th month. The experiments above having been commenced the middle of November, the greatest resistances correspond to the months of July, August and September. The mortars were deposited in a cellar; but the cellar was one to which external differences of temperature were soon transmitted. In summer, therefore, these mortars were exposed to an atmosphere humid and mild.

The series No. 3 differs from the first only in the lime having been slaked to a thin, instead of a thick paste. The lime was left six months before making any mortar with it. We see that the results were the same, that is to say, were equally bad with those of the first series.

The fourth series differs from the second only in being made of lime slaked thin, while the second series was slaked to a thick paste. I only began to make the mortars after six months had elapsed. We see that the results are good, but rather inferior to those given by lime slaked to a thick paste.

Series No. 5 was made of the same lime, slaked to dry powder. This series was not commenced till six months after the slaking of the lime. The mortars I obtained had no consistency, and crumbled easily between the fingers. The mortars of the first and third series, made at the same period, bad as they were, gave resistance enough to be submitted to fracture. The lime of series No. 5, was slaked by a process analogous to that of Mr. Lafaye, which consists, as I have stated, in plunging the lime for a few seconds into water, then withdrawing it, allowing it to slake of itself, and keeping it for some time before using it; to avoid the embarrassment of the baskets proposed by Mr. Lafaye, I contented myself with throwing on the lime the quantity of water necessary to reduce it to powder, which, in fact, amounts to the same thing. I however obtained no result. It is possible that Mr. Lafaye made his experiments a short time after the slaking of the lime, and comparing them with others made of lime slaked and lying wet for a long time, he found the first to be the best; but it was probably because the lime he employed, like that in the above table, required to be used immediately after being slaked. It appears to me that Mr. Lafaye was deceived in attributing his success to the mode of slaking which he followed. The experiments of table No. VI were also made with lime slaked to dry powder, mixed with sand and trass. I did not commence these trials till after six months, and I was only able to continue them four months, for want of time. The results are about the same as those of the fourth series, and a little inferior to those of the second.

In the first four series, the proportions were one part of lime in paste, to

two and a half parts of sand and trass. To obtain results with the last two series in which the lime was slaked to powder, that might be compared with these, I took care, when making the mortars of the last two series, to reduce this powder to paste, and to measure it in this state.

If we compare the above table with table No. XV, whereof the mortars were made of the same lime, we shall see that in general the mortars left in the air gave results a little weaker than those put in water.

Table No. XXX has shown the bad quality of mortars made by mixing sand with fat lime that had been slaked and wet for some years. The following are corresponding experiments made with the same lime just from

the kiln.

Observations on the experiments of Table No. XXXIV.

The experiments of table No. XXXIV, were made with lime just from the kiln. The mortars were made immediately, and with a view to ascertain the quantity of sand which this lime would bear. The results shew that the greatest resistance corresponded to one part of lime measured in paste, and two parts of sand, and that the resistances diminished in proportion as the sand was increased. No. 4 had so little strength that it was unable to support the weight of the scale pan; and No. 5 crumbled readily between the fingers. The proportion in general use is one part of fat lime measured in paste, to two parts of sand. Some constructors think that more sand is requisite, but the trials in table No. XXXIV, do not at all confirm this opinion. I regret not having begun by putting a smaller proportion of sand; these experiments should be repeated.

The experiments of tables Nos. XXX and XXXIV are the same, with this difference, that in table No. XXX, lime which had been slaked and lying wet for some years, was made use of, while, in table No. XXXIV, the mortars were made of lime as soon as it was taken out of the kiln. In table No. XXX, with the old lime, I could get no results, whatever were the proportions; while with the same sort of lime fresh from the kiln, the mortars gave some resistance. I do not know how to account for the mortar No. 3, above, being more than one half weaker than mortar No. 1, of table No.. XXXIII, which was made and proportioned in the same manner. The differences may be owing to the degree of burning of the lime. It appears to me that fat lime loses quality by being worked up with too much water; but I made no experiments to determine the quantity of water proper to be put in these kinds of mortar; these experiments are yet to be made. It

results, nevertheless, from the experiments given in the first section, and from those given above, that lime, whether common or hydraulic, does not bear as much sand as is commonly thought; but it appears to be able to bear more trass, whether alone or mixed with sand; which may be attributed to the combination that takes place, in the moist way, between the trass or puzzolana, and the lime. I purposed making some essays with a view to ascertain the quantities of sand and factitious puzzolana that ought to be mixed with fat lime to give mortars of good resistance; but these proportions can only be fixed after numerous trials, and almost all my leisure had been absorbed by my researches as to factitious puzzolana. I should want, before undertaking the experiments on the proportions of mortars, to have some fixed data, so as to avoid too great a number of useless trials. This is a labour that remains to be undertaken; and it will, no doubt, give different results, according to localities, and according to the quality of lime and factitious puzzolana employed. On summing up, it will be perceived that by whatever manner I operated, only indifferent results were obtained by mixing fat lime with sand; while I obtained very good results by mixing one part of fat lime, measured in paste, with two and a half to three parts of sand and trass taken in equal quantities; as may be seen at the end of table No. XXXI, and in the series No. 2, of table No. XXXIII. It will no doubt be objected to me that several demolitions have been made of masonry built of fat lime; and that the mortars have been found very hard. I will answer this objection; but I am first obliged to present several other experiments.

CHAPTER XII.

Of mortars made of Hydraulic lime and sand, or of Hydraulic lime and Puzzolana.

After I had become acquainted with the good qualities of the Obernai hydraulic lime, I used it not only for works in water, but also for masonry in the air. It required some patience to change the habits of the workmen, and to bring them to the use of other means than those they had been accustomed to apply to the slaking and management of fat lime; but I was ably seconded by Lieut. Col. Finot of the Engineers, who was charged with the immediate superintendence at Strasburg; and, thanks to his efforts, all the persons employed soon became familiar with the manner of treating hydraulic lime, and excellent results were obtained.

In the observations made by Mr. Vicat on the pamphlet published by me in 1824, he thus expresses himself: "Mr. Treussart pretends that hydraulic limes are only made in order to obtain mortars which will harden in water: so far from that being the case, it may, on the contrary, be said, that hydraulic limes (when the country does not furnish them naturally) are made only because mortars composed of these limes and common sand are, at the same time, the most economical and the best, that have yet been discovered, to brave the inclemences of the weather, resist the alternations of hot and cold, wet and dry, &c."

It is true that at page 46 of my pamphlet I said "The author observes that hydraulic limes are made only to compose mortars which have the property of hardening in water. Since this result is obtained, directly, with fat lime and factitious trass, and the results thus obtained are the best, he thinks this mode the most advantageous." This passage cited independently, might lead to error: but, as in all that preceded, the question was, only, as to works in water, it means that when there are works to be built