placed horizontally, meeting the model on one side and the vertical piece on the other; its ends are therefore cut to correspond respectively with the surface of the vertical piece and with that of the model; its form is flattened. The first of these pieces of wood is called simply the gate, the other the heel. In describing the process of casting we shall mention the several instruments made use of; but we must first say a few words on the subject of the lathe used for forming the cores made of clay, and the nucleus of those made of sand. (TO BE CONTINUED IN OUR NEXT.)

On Calcareous Cements. By JAMES FROST, Civil Engineer.

No. IV.*

FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

Having seen the intense affinity between lime and water, we will now endeavour to examine the superior affinity between lime and carbonic acid; with which lime is always found naturally and definitely combined in the proportion of twenty-eight lime and twenty-two carbonic acid. It is also, generally or always found mixed, and seemingly in combination with other substances; for, in the purest white Italian marble I have always found some minute silicious particles. Yet, carbonate of lime we shall hereafter find is never chemically combined with those other substances-whatever may be the hardness or specific gravity of the mass;-and as this is seemingly a position of some importance in geological investigations, it will be hereafter adverted to in connection with another part of equal importance, when we have had the advantage of considering some other combinations of lime.

In England, lime is generally procured by calcining the carbonates in two different modes. The one and most frequent, is the cheapest and easiest in practice, but the lime obtained in this way is generally found inferior in quality to that obtained by the more troublesome and expensive process.

As lime of as good quality may be obtained by the easier process, we will endeavor to describe the necessary conditions. In the first mode, the carbonate is interstratified with the smallest and cheapest coal, in inverted lime kilns, and the fuel being in actual contact, acts with the greatest effect. The kilns are of the cheapest construction and maintenance, and being daily emptied of a portion of calcined lime, and daily charged with an equal proportion of fresh materials, the business is regularly conducted in the easiest manner-but the lime thus obtained is of a variable quality from some causes which must be explained in order to be avoided.

In the second mode the carbonates are piled in kilns so constructed that the fuel is burned in furnaces, and only the flame thereof admitted into the kilns to calcine the lime. In this mode, the coals used are large and of the dearest kind; more of them are required, as they do not act with so much effect; constant attendance is required night and day during the calcination; the kilns are more costly in construction and maintenance, and much expensive iron work is required.

If we calcine some limestone in an iron tube, or retort, set in a brick furnace, and then allow the retort to cool very slowly, while another portion of limestone is being calcined in a similar retort which is connected by an iron tube with the first so that the carbonic acid gas may be conducted

* No. III. was published in the April number of this Journal, page 234. vo!. XVII.

into the first retort, it will be there absorbed by the hot lime, which thus becomes uncalcined as it were, and is recarbonated more or less according to the care taken in conducting the experiment.

If we now enquire why the first mode is so uncertain, we shall find that the kilns are commonly constructed about equal in diameter and depth, and that the most careful workmen find it difficult, or impracticable, to draw the calcined lime, so that portions of it do not intermix with portions of the uncalcined and of the fuel. In which case, a portion of uncalcined lime escapes calcination, and a portion of that which is calcined becomes more or less uncalcined, and a very irregular article is thus produced.

If lime kilns were always constructed of two or three diameters in depth, careful workmen might always draw without intermixing the calcined and uncalcined strata in the kilns, and a good article would always be produced at the least expense of time and trouble, and that this mode will succeed in practice with any description of limestone, will be apparent, when we state that the most difficult carbonates to calcine, are those employed in the production of cements, which must be sufficiently calcined to become tender for grinding, while from their chemical qualities they are easily fusible with a small excess of fuel; now as these carbonates are well calcined in such kilns, it must be evident that all may be so, as no others can, from their nature, be so difficult to manage.

In either of the two modes of calcination the lime is allowed to cool in contact with atmospheric air, and this we have already seen is essential to the production of lime. For, if having calcined lime in a reverberatory fur nace, wherein coke has been used for fuel, and if then a fresh supply of fuel be added, and the supply of fresh air prevented to the furnace and to the chimney, by closing the apertures thereto, and the lime be thus allowed to cool, it will absorb and condense much sulphuretted hydrogen as well as carbonic acid gas, and when cool, will be incapable of slacking with water, and if pulverised and tempered with water, it will set as cement, for a long time thereafter, exhaling the peculiar odour of sulphuretted hydrogen.

If, when the lime is about to be thus cooled in a reverberatory furnace, a portion of pine wood is added to the other fuel, the lime when cool, will be found nearly black throughout its whole substance by the vapour of carbon which has penetrated and been condensed therein; a black cement has been thus obtained, coloured probably, as some black marbles are found by analysis to be; the Kilkenny or black Irish marble, owing its color to its containing two per cent more carbon than white marble, which always holds twelve per cent combined with oxygen in its carbonic acid, and Kilkenny marble holds only two per cent more, but being uncombined, it acts as colouring matter, showing what a great difference in sensible qualities is made by a small difference in the quantities and chemical arrangement of the elements of solid bodies.

Every different species of carbonate requires a different quantity of fuel for its due calcination, the argillaceous varieties requiring a quantity very nearly proportioned to the carbonic acid in them; hence, the inference is, that the heat evolved is essentially employed in converting the acid into permanent gas. Thus, two measures of small Newcastle coals, are required for the calcination of ten measures of Thames chalk, and is sufficient for fifteen measures of Roman cement stone; but as this latter substance is about one third ferruginous and argillaceous matter, it would seem to require the expenditure of little fuel for that portion. As a measure of chalk is about

twice as heavy as a measure of coals, it follows that, ten pounds of coals are required to calcine 100 of carbonate, or one pound coals to 4.4 pounds carbonic acid; but as eighty-four pounds of the live coals would heat and evaporate twelve cubic feet of water, one pound of coals would heat and evaporate nine pounds of water. We thus find by rather a rough process, but from facts correct enough for general reasoning, because derived from operations conducted on the large scale, that the latent heat in carbonic acid gas, is about double the latent heat of steam.

If 37 parts hydrate of lime is placed in contact with 22 carbonic acid, the nine parts of water in the hydrate will be all expelled, and the carbonic gas combining in a solid form with the lime gives out its latent heat, which being taken up by the water, it escapes in the form of vapour, or steam of superior elasticity to the atmospheric pressure, although its temperature is insensible, this very curious or rather wonderful fact, and others, hitherto, I believe, wholly unnoticed, we shall see amply verified when we examine the properties of cements.

FOR THE JOURNAL OF THE FRANKLIN INSTITUTE.

On the Production and Manufacture of Salad or Table Oil in the United States.

The following remarks are intended to apply to that strip of the United States, which is comprehended between the latitudes of Cape Hatteras and Boston bay, extending westward.

Although there is no part of this extensive region in which the olive tree could be cultivated, except when protected by the green house, and therefore, the inhabitants are denied the advantages of this useful tree, it does not follow, that nature has denied them the means of procuring an excellent and pleasant substitute for olive oil, and one that could be brought into market at a moderate cost. Between them and this enjoyment, ignorance is at present a barrier, and in this case, as in many others, this is strengthened in its result, by prejudice.

In French Flanders, the farmers cultivate in large fields, and to a great extent the White Poppy. The seeds of this plant are collected and bruised in some way, and an oil expressed from them, which in all respects resembles olive oil, and is the source from whence is derived a large proportion of what is consumed in Paris. The poppy oil so much resembles olive oil, that strangers who visit Paris take it for that oil. These are facts as regards the consumption.

Of the state of this important branch of husbandry and manufacture, we the people of the United States know nothing. How is it cultivated, the seed collected, the oil preserved? Does the land require to be sown every year, or does it seed itself? What sort of a mill does it require? What is the product in oil, or in profit? In short, we have every thing to learn, except that, incidentally we have heard that fifty pounds of beet cake, after the sugar maker has got what he wants out of it, and ten pounds of poppy seed after the oil maker has done with it, will keep ten sheep a day and fatten them.

We know that since the article on beet sugar appeared in the Journal of the Franklin Institute, requesting those who knew any thing of the subject to favour the editor of the Journal or the public with information, a well

qualified agent has been sent to Europe to acquaint himself with the whole agricultural and manufacturing business that produces sugar.

On the present occasion, we invite the patrons of our country's industry and resources, to communicate for publication, what they know on the above interesting branch of French husbandry, &c. And we therefore request the wealthy and patriotic, to consider whether the case of oil does not resemble that of the sugar from the beet, and whether the best course would not be to adopt a plan similar to that which the friends of beet sugar have chosen.

The time will come when American parents will send their sons to Europe and to other foreign places, to learn the manufacture of beet sugar, of oil, and such other branches of the arts not possessed by us, in the same manner and with better reason that they now do to have them learn medicine and surgery:

June 4, 1836.

J. R.

Civil Engineering.

Some suggestions on the Location and Grading of Rail Roads.

By THOMAS EARLE.

In the location and grading of rail roads, it is usual to reduce the road in all parts, as near to a level as possible, and in effecting this object, to make many curvatures, some of them of small radius. Thus, a very considerable increase of expenditure and of distance is occasioned, which appears to me inexpedient.

It is true, that if a rail road could be made perfectly level, or very nearly so, without being unreasonably curved, such a road would be better than an undulating one: because the locomotive engines would require to be transported less frequently over the ground, to convey a certain quantity of goods on such a road, although the expenditure of steam for conveying the train, independent of the locomotive, would be as great on the level road as on the undulating one. A perfectly level road, however, is impracticable in most parts of the country, except at an expense far exceeding the value of the benefit gained. Hence, it is probable that few roads will hereafter be made, without ascents and descents, in some parts, at the rate of forty to fifty feet per mile.

Such ascents being admitted in some parts of the road, the locomotives will take no greater trains than they can draw up those ascents. Hence, it will be useless to make excavations, embankments, and curvatures, to avoid other ascents of the same grade.

A locomotive will take a train up an ascent of twenty-one feet to the mile, and down a descent of the same length and grade, with precisely the same expenditure of steam, if it be constantly used, as would be required to take the same train over the same distance, on a perfect level. If the train were such as to require for drawing it on a level, a pressure of steam on the piston of thirty-six pounds to the inch, above the atmosphere, then on the ascent of twenty-one feet per mile, it would require sixty-three pounds per inch, and on the descent of the same grade, nine pounds per inch, making the average thirty-six pounds or the same as on the level. Thus, 63+7= 72÷2-36 pounds.

If, however, the road were composed of alternate ascents and descents, at the rate of from thirty to forty feet per mile, with but short levels between them, the engine would transport such train as it could draw on the road,

with a less expenditure of steam than it would require to transport the same train on a level. This might be effected by shutting off the steam from the piston on descents, and suffering the train to progress by its own gravity. The saving in this case, compared with the other, would arise from dispensing, on half the distance, with the amount of steam, viz: about fifteen pounds to the inch, which is required to overcome the external resistance of the atmosphere. There would also be a further saving from the constant use of high steam, if the supposed fact be correct, that a certain volume of steam under a pressure of one hundred pounds to the inch, can be produced with less than double the fuel which is required to produce the same volume of steam under a pressure of fifty pounds to the inch.

And the result, as to the expenditure of steam, will be equally favourable on ascents and descents, as great as fifty feet to the mile, (excepting the before-mentioned inconvenience of transporting the engine a greater number of times over the ground) as with ascents and descents of a less grade, provided the inclined planes be not so long as to require the checking of the velocity of the train, by artificial means in descending: for the momentum acquired in the descent, will continue the motion on the succeeding level or ascent, until the power expended in overcoming gravity in ascending, is reimbursed.

It is further to be observed, that if there be admitted on a road, inclined planes of several miles in length, and of a certain grade, shorter planes of a higher grade may be admitted on the same road, without inconvenience, because the momentum acquired by the velocity of the train, before commencing an ascent, will give considerable assistance in overcoming it. A velocity of twenty miles per hour would give a momentum, if I have estimated it rightly, sufficient to raise the train about twelve feet in perpenticular height. Thus a road having long inclined planes, graded at forty feet per mile, will admit those not exceeding two thirds of a mile in length graded at fifty feet, or not exceeding one third of a mile in length, at sixty

feet.

Hence, it is unnecessary, on long inclined planes intended for locomotives, to make them of uniform ascent, as the momentum gained where the ascent is below the average, will assist in overcoming the resistance where it is above.

The making of curves in rail roads, to avoid slight ascents and descents, is productive of several inconveniencies.

1. It increases the cost of the road, by its greater length, and proportionably greater expenditure for land, foundation and rails.

2. By the increase of length, the time of travel and the expenditure of steam, is increased in nearly the same proportion.

3. The expenditure of steam is further increased, in overcoming the strain and friction occasioned by the operation of the wheels on the curves, the power expended not being re-imbursed, like that expended in overcoming ascents. The resistance on short curves upon a level is found to be greater than on a straight ascent of thirty feet per mile.

4. The wear of carriages and locomotives, and their liability to break or become disordered, is increased by the greater distance, and by the strain on the curves, which racks every part of the machinery to a degree much complained of by practical engineers.

5. The wear of the rails, and their liability to disorder is increased. 6. The danger of running off the road is increased.