In burning, it is necessary to keep the fire up at a regular red heat, and not to make it too powerful, or it will cause the lime to vitrify, and the surface of the lumps being thereby covered with a glazed coating, will be rendered useless.

The coal used is small, almost dust, and passed through a screen to give it uniformity, a shed should be provided for it, to keep it dry, and as near the kiln as may be found convenient. If a shed, or some such shelter, were erected for the limestone also, it would be found advantageous: for when taken from the pit, even in the dryest weather, it contains some moisture, but in rainy seasons, in consequence of lying round the kiln in small heaps, it is often completely saturated with wet before it is put in the kiln, which causes an otherwise unnecessary quantity of fuel to be expended upon it. Breeze, such as is used for burning clamp-bricks, is also, by some, used in burning lime, either alone, or mixed with small coal.

CAPTAIN SCOTT'S CEMENT.

A new principle in the formation of cement has lately been applied by Captain Scott, R.E., viz. that of producing one of hydraulic properties by "subjecting lime in a heated state to the action of sulphurous acid." In describing it he says:—

"In carrying out this process the following method is at present practised; quicklime, prepared in any of the ordinary methods, is placed on a perforated arched floor in a layer 3 feet deep, having beneath it a fire-place 1 foot broad, with cheeks sloping outwards to the full width of the kiln, and extending throughout its whole length. The fire-bars are 1 foot 3 inches from the ground, and the perforated fire-brick arch con. sists of two 44-inch rings, 3 feet 6 inches above them. The whole is covered in with a 9-inch semicircular arch, springing 2 feet 6 inches above the perforated floor.

"At the end of the kiln furthest from the fire-door, is a hatch or opening 2 feet 6 inches wide and 4 feet high, for charging and drawing. This is closed during the process with a double wall of bricks, having an intermediate space of a few inches filled with lime dust. The chimney is over the hatch, and is raised about 1 foot above the outer ring of the semicircular arch which forms the roof. The kiln is 6 feet long and 2 feet 6 inches broad, and therefore in a depth of 3 feet contains 3 cubic yards of lime. The kilns which the manufacturers propose to erect (that above described being intended for experimental purposes only) will be about 23 feet long and 10 feet wide, with four fire-places, two at either end, separated by a wall of brick extending to the height of the perforated floor. In other respects they will differ little from the small kiln here described.

"When the charge of lime has been raised to a dull glow, the firing is raked out and 30 lbs. of sulphur are introduced into the ash-pit in iron pots. As soon as this sulphur is fully ignited, the chimney is shut up and the ash-pit and fire-door closed, some little air still finding its way in and continuing its combustion. At the end of 7 or 8 hours (in a 3-bushel kiln I find 2 hours sufficient) the charge is raked out, ground to powder, and packed in casks for use. This process is applicable to any lime. The nature of the lime, as respects its mode of combining with water, is now completely altered, for instead of slaking, it will, when mixed with it, gradually harden into a stone-like substance."

This cement, according to Messrs. Lee and Co., the manufacturers, possesses, for internal purposes, all the valuable properties of the Parian cement except whiteness, and can be employed more cheaply than ordinary lime and hair plaster; and for hydraulic purposes is superior to the much esteemed Lias Lime.

* Brush-wood, furze, timber, and turf or sod, answer sufficiently well for the purposes of hutting. -Editors.

Instructions for Use.

"The cement must be kept dry and protected from the air. Use 3, 4, or 5 parts of sand to one of cement, for rendering, and 3 of sand, or less, to one of cement for finishing, according to the work required. The sand to be clean and sharp, and for the rendering coat coarse.

"The surface to which it is to be applied must be well wetted, particularly if the brickwork be old. If this precaution be not attended to, the cement is robbed of the water which is necessary to its becoming a solid mass, and crumbles from the wall. The effect will occur within one or two days.

“In summer time, if exposed to the sun, the cement should be occasionally wetted for a day or two, to prevent a too rapid desiccation, which detracts from the hardness it is otherwise capable of assuming.

"If used for moulding (when 1 or 2 parts of sand to 1 of cement may be employed), the cast must be well wetted, or, still better, immersed in water for an hour or two, before it has become thoroughly dry. For mortar, use 3 or 4 parts of sand to 1 of cement. For concrete, treat it like ground Lias Lime."

LOOPHOLE.*. -The term "loophole" is understood to denote the opening in a masonry wall or stockade, for the use of musketry, as an embrasure is for that of artillery.

The nearly uniform dimensions of all infantry muskets of the present day, and a due attention to economy and convenience in building, have reduced the form of the loophole to two or three conditions, adapted to suit the purposes of defence.

It is usual to distinguish these by the direction of the exterior opening. Thus we call the loophole vertical or horizontal, according as the exterior opening is upright or the contrary.

The vertical construction is best adapted for sites where great vertical range is required, such as for the flanking of high scarps, or steep slopes, etc.

Under all other circumstances, the horizontal loophole will be found most effective and most convenient. It affords greater advantages for defence, because, with great lateral extent, it combines sufficient vertical range to include the height of a man, which, under ordinary circumstances, is all that will be required.

The interior opening of the loophole can be of the same form in both these conditions: for a man to use his musket conveniently, it should not be less than 2 feet wide and 1 foot 6 inches high. Vertical loops are seldom constructed for more than one man to serve at a time; and in brick walls they are placed with their centres not less than 3 feet apart. Horizontal loops, on the contrary, can be constructed to contain two or even three men, the interior opening having an increase of not less than 2 feet per man.

The extent of the exterior opening depends upon the range required, but its width should not exceed 3 inches, and the hole at the exterior should be at least 7 or 8 feet above the level of the ground at the outside, to prevent the loop being marked or fired into.

The length of barrel of a musket in our Service is about 3 feet 3 inches. As it is necessary that the muzzle should extend 3 inches outside of the loop, to pre

By the late Colonel Tylden, Royal Engineers.

We do not concur; we conceive that the vertical loophole facilitates the command of the ground in front, and enables the soldier to deliver his fire with greater ease. In galleries for reverse fire and caponnières to flank the ditches, the horizontal loophole may be preferable.-Editors.

Plate I.

figs. 1, 2, and 3.

vent inconvenience from the explosion, it is evident that the ordinary form of loop is inapplicable to a wall of a greater thickness than 2 feet 6 inches, or at most 3 feet. When this dimension is increased, it becomes necessary to make a corresponding modification in the arrangement of the loop.

Let us take 3 feet as a convenient thickness of wall, and construct the loop either vertical or horizontal, as before described.

Then, for any additional exterior thickness of wall up to 5 or 6 feet, the sides of the loop can be formed in successive courses of bricks, as described in the late Lieutenant-Colonel Alderson's Memorandum in the eighth volume of the Professional Papers,' which is given at length in this Article.

But when the thickness of wall exceeds 6 feet, this method will be found inconvenient,

Fig. 1.

6.6

on account of the great increase to the exterior opening; and in this case it is usual to form an arched recess in the interior, of whatever additional depth is required to make up the thickness of wall.

Fig. 2.

The recess may be made to contain three or four loops, as may be convenient, and if the piers and arch be carried through to the exterior, the formation of the recess does not so much tend to weaken the wall.

The following excellent method of forming horizontal

MA

3.0

loops in brick-work has been suggested by Lieutenant-Colonel Alderson, R.E.
"Horizontal loopholes present a much wider range of fire than vertical ones, for
the space exposed; and in boundary walls, defensible barracks and guard-houses,
reverse fires, and caponnières, are decidedly preferable.

"The present horizontal loophole is a cast iron frame, built into the wall so as to
weaken it as little as possible. It is adapted for a wall three bricks thick.
"The same principle may be adopted in walls of any thickness.

"Fish-belly girders (a, a, a) are provided to strengthen the upper part of the loophole, and enable it to carry the wall above. Arches, however, may be turned as over window openings, if preferred. Half-inch iron will be sufficient for the sides and bottom of the frame.

"By giving the loop-hole the present form, it sets with great firmness in the wall.

"In reverse fires and caponnières, whose object is the defence of the passage of the ditch, when the enemy is otherwise occupied than in returning the fire of them, external objects will be better seen by making the larger opening of the loophole outside, in which case the smaller opening may be increased from 4 to 6 inches.

"In boundary walls, barracks, and guard-houses, the larger opening should be inside it will afford in the two latter more light, and provide shelves for the occupants; and in the former it will present a smaller object, and make the opening higher from the outside.

"Loopholes should always be higher or lower than a man's height from the level of the ground immediately in front of them. When this cannot be effected, there should be a drop or ditch in front.

Plate II. fig. 3.

Plate III.

figs. 1, 2, and 3.

"Six feet is the length of the larger opening of the present loophole frame, which may be considered as a maximum, to be reduced according to circumstances. towers or other works situated on high and commanding points with no level ground within range, the section described by fig. 4, Plate I., is recommended.

In

"These loopholes, though here represented of cast iron, may also be made of slate, or hard stone."

The above observations are chiefly applicable to the loophole when formed in brick; but when the wall is of stone, or the loophole itself set in stone in a brick wall, we are enabled, by a modified arrangement in the sides of the loop, to give much greater security to the defenders without entailing a great increase of expense.

a b c d is a loophole to be served by two men, and requiring a horizontal range of 120°. A length of six feet for the interior opening will afford ample space for two men to serve at once. The thickness of wall is taken at 3 feet, and if the lines limiting the lateral range be produced, they will give an exterior opening of about 4 feet inches.

'It will now appear that if the lines a c-b d were to form the sides of the loop, the greatest protection will ensue to the defender when the opening at e is as small as possible.

It is necessary, however, that both men should be enabled, if required, to fire direct to the front; and a due regard to light and ventilation will not allow of this opening having a less length than 2 feet, so that the vertical area of the opening at this point will be about 2 feet by 11 inches high.

To ensure resistance against a musket-ball, and to give proper strength to the side of the loop where a soft stone is used, the thickness f g should not be less than 6 inches, though it will be of advantage to diminish this dimension whenever a harder. material will allow of it.

The sides gbh e forming portions of the lines limiting the lateral range of the loops, the lines kf-li are directed on the angles h and g, and lines drawn from a and d, to intersect them at k and l, and forming an angle of 40° with af and di, it being assumed that a bullet will not effectually reflect from a wall at a greater angle.

On examining this construction it will be evident that no bullet can possibly reflect into the interior after striking the side of the loop, except upon the small portions fg, hi; and that while the range of 120° is preserved, the vertical space through which a bullet must pass to enter the interior is only 2 feet long by 3 inches high.*

A construction something similar to that just described will be found in a Paper by Lieutenant-Colonel Ord, in the eighth volume of the Professional Papers,' and drawings of which are given in Plate III. figs. 1, 2, and 3.

“Figs. 1 and 2 represent a simple horizontal loophole for two men to fire through. They should be, when practicable, made of cut stone throughout: if of brickwork, the head should be arched, as shown by dotted lines in fig. 4, the sides of common brick, and the holes of good hard Dutch clinkers or fire-bricks (when manufactured of a hard nature), and set in cement.

"All the four sides have one break on return, offering an important obstacle to balls from without, whether from a direct fire, or after having been reflected from some other object.

The dimensions in the diagram are merely assumed to illustrate the principle, which is applicable to any variation either in the thickness of wall or size of loop.-R. T.

Plate III.

"The zigzaged loophole (fig. 3) is a plan that may be adopted with great advantage, where it is desirable, or even convenient, to have the mouth of the loophole towards the enemy, and which, in consequence of the numerous "facets" covered with sheet iron, will be found to afford scarcely less security than the plain-sided one, with the narrow opening outwards."

The following description of Lieutenant-Colonel Ord's loopholed window for defensive barracks, etc., and other buildings requiring a reasonable supply of light and ventilation, is taken from the same Paper.

Figs. 4, 5, 6, 7, represent the loopholed window. The dimensions, when the window is to be used as a loophole, are the same as those in figs. I and 2, Plate III., and this is effected as follows: a wrought iron abattant, or falling shutter, is attached to the head of the iron window frame by means of a pivot or hinge, the two ends working in iron eyes or rings. The pivot is of round bar iron, with the sheet iron forming the abattant riveted to it; this abattant is lowered to the iron rests (see fig. 7), and thus forms a very complete loophole. When employed as a window, the abattant is raised by winch-handles, which are fixed on the square ends of the pivot or hinge, and, being bolted, remain continually up.

"The iron sashes are removed for action, and the loophole is then clear.

"By examining fig. 7, it will be clear that no injury can be done to the defender by shots between the abattant and the head of the window above it, unless the firing should be of such a nature that an ordinary loophole would be almost destroyed by it.

“Plates are riveted to the angles of the abattant to strengthen it. The necessity for them, and their dimensions and numbers, would be left to the discretion of the Engineer, as the strength required would of course vary according to the fire likely to be brought upon it, which would depend on the locality.

"The loopholed window should also be in cut stone, whenever practicable. "This window may be lengthened to 6 feet when necessary, this length being the maximum."

Great difference of opinion exists in our Service with regard to the comparative advantages of loopholed fire and that of the ordinary parapet; but in sites liable to be commanded within musketry range, and unexposed to the fire of artillery, and for the close defence of the ditches, etc., of permanent works, the loophole presents most unquestionable advantages.

The general application of loopholed fire in all fortresses recently erected or in course of execution on the Continent, together with the attention paid to the direction and construction of the loops themselves, afford ample evidence on this point. It would appear that the vertical construction is almost universal in these works.* Figs. 1 and 2, Plate II., are descriptive of the arrangement of some loops at Grenoble, and form a good example for the adjustment of vertical loops upon uneven ground.

Respecting the local distribution of loops, no positive rules can be laid down where everything depends upon the nature of the site. The following observations may perhaps be of general application.

Where the loops are formed in long continued walls properly flanked by artillery or musketry, such as in the gorges of large works, they can be dispersed at longer intervals, in proportion as the command of the ground immediately in front of them is of more or less importance.

From Captain Maurice's Essai sur la Fortification Moderne.'