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spindle opposite to the core, should be perfectly equal to their corresponding parts in the spindle of the model, and that the length of the swell be strictly determined according to the dimensions of the flask. We shall return to this subject.
The spindle may be either solid or hollow. Solid spindles having one or two deep grooves extending through their whole length, are also pierced, at the part which supports the core, with two rectangular holes in which pieces of slate are placed, to support the clay. In these grooves are placed straws to facilitate the disengaging of the gases. Hollow spindles intended principally for cores of sand, are pierced with five or six holes two lines in diameter. I think the latter kind preferable; they are besides easier to make, lighter, and less apt to spring than the solid spindles; they are made of sheet iron fifteen or twenty points thick, cut into pieces of proper size and rolled hot on a mandril. It is not necessary that the edges should be brazed together; it is sufficient that they join. The swell of the spindle is made by a ferrule which is brazed on. It is essential that the ferrule and all that part of the spindle which is to be similar to the spindle of the model, should be turned to the exact dimensions required. Both kinds of spindles should be flattened at the end opposite to the core, in order that it may enter into a crank; in that part there is also a hole to receive a key, when the core is placed in the mould. The other end should have a small conical indentation to receive the point of the screw which serves to fix the spindle in the lathe.
The dimensions of the core are determined by means of wooden patterns, of which there should be three, because the core is not finished at one operation. The radius of the first pattern differs ten 'lines, of the second four lines, from that of the core when finished; the third should give an exact section of the core, including that of the eye. The pattern is very easily drawn, for all its dimensions are given by those of the shell. A similar profile, made of iron, a gauge, and calibres for the eye, serve to verify the dimensions of the core. Before entering into the details of moulding, we shall describe
Of the Flasks.
The flasks are boxes of wood, or of cast iron, without bottoms, divided into two unequal parts, each of which contains the mould of a hemisphere, and which are joined together by dowel pins, wedges, hooks, or small bolts and keys: the connexion by means of screws seems to me very defective.
The thickness of the boards of which wooden flasks are made should be from fifteen to eighteen lines for ten and twelve inch shells, and from ten to twelve lines for other projectiles. Wooden flasks are generally square; three of the angles are partly filled by triangular prisms of wood, to increase their solidity and diminish their capacity. The size of the flasks should be such as to leave a space of about an inch, or an inch and a half, around the model: if this space were greater, the preparation of the mould would require too much time; it would increase the expense, and at the same time impair the result of the operation, because the sand always yields more or less to the expansion of the metal, which is greatest at the points of least resistance, and this effect will be greater where the sand is thicker, the difficulty of ramming it firmly, being then increased. The part of a flask which contains the mould of the hemisphere in which the eye of a shell is placed, we shall call the drag; the other part the cope. The former which is ten inches eight lines deep for twelve inch shells, and to which the slides that receive
the wedges are adapted, contains a cast iron traverse, reinforced in the middle of its length, and pierced with a hole. The depth of this hole, or the thickness of the bar, or traverse, is four inches; its width is arbitrary. The hole, which is nine lines in diameter, receives the spindle of the model, the swell of which should rest exactly against this bar, as should also the swell of the spindle of the core. Accuracy in the position, and consequently in the thickness, of the sides of the projectile, depends therefore on the precision with which the bar is made and fixed in its place, as well as on accuracy and perfect identity in the form of the spindles.
This bar, or traverse, is therefore the most important part of the flask. If it were bent up or down the thickness of metal at the eye would be too great or two small: if its position were deranged laterally, the position and direction of the eye would vary accordingly. In verifying the flasks therefore the principal attention should be directed to the position, dimensions, and solidity of the traverses. They are let in their whole thickness into the sides of the flask, and kept in their places by screws, straps and keys. The depth of the drag is generally determined by the semi-diameter of the model added to the height of the swell of the spindle, and the thickness of the traverse. The sum of these three dimensions is ten inches eight lines for a twelve inch shell. The depth of the cope is equal to the semi-diameter of the model increased by two or three inches allowed for the thickness of the coat of sand: that depth is consequently from eight inches to nine inches in the example we have chosen. It may without inconvenience, be greater; but no variation can be allowed in the depth of the drag, unless corresponding variations are made in the spindles or in the thickness of the
When the flask is so arranged that the shell is cast with the eye downward, it is necessary to give the cope a greater depth than it would require if the shell were cast with the eye uppermost; because in the former case the sand in the cope is supported by the board on which the flask rests, but not in the latter.
Cast iron flasks have a round form with a swell or projection at the part where the gate is placed. The sides may be vertical, or may consist of two truncated cones placed base to base, giving a swell in the middle of the height. The two parts are connected together by dowels and ears through which key bolts pass. The traverses should be cast separately, and the holes drilled cold, to secure greater accuracy. In casting them at the same time with the flasks it would be impossible to avoid slight variations in all their dimensions; cast iron flasks are far preferable to wooden ones, because they can be better joined, and are much less subject to derangement, and the traverses can be adjusted in them with greater precision and solidity. We have already said that there is an advantage in having the coat of sand thin; but in that case the wood, affected by the heat and steam, becomes warped, which always causes errors in the dimensions of the projectile:
hence another reason in favor of cast iron flasks.
The gate or channel by which the metal is conducted into the moulds is curved and terminates at the extremity of a horizontal diameter of the mould. It is called a heel gate, and it is formed in the sand by two pieces of wood, one of which, placed vertically, has a conical form: the diameter of its greater base is two and a half inches, that of the lower base is nine lines for twelve inch shells, and its height is necessarily equal to that of the upper portion of the flask: the other piece of wood which forms the heel, is
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.
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 kilos 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. vol. 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