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advantages over straight rafters and upright and sloping glass, that they will soon in all probability take place of every other plan.

Though curved rafters may be placed at double the distance of the common sort, and consequently must sustain double their weight, yet they may be made still lighter than those just described. In short, an astragal of wrought iron drawn of double the usual size, would form a sufficiently strong rafter for all the ordinary purposes of convex roofs.

Fig. 3, PL. X., exhibits three different rafters of cast iron, each twenty-five feet long and placed six feet asunder, in all of which the under rib or rod, a...b, with or without a water gutter attached to it, is intended to support a vine. If the house were narrower,—that is, if the back wall were in the situation of the perpendicular lines, c, d, or e,—. then of course the rafter would be made lighter; and if wider, as for such houses as that in PL. IV., stronger, and the braces differently arranged. Any one who has studied with attention the roof of the Halle au blé in Paris, need not be told that where a curve is the form given there is no known limit to roofs of this description.

Figs. 4 and 5 are sections of the rafter, showing different modes of attaching wires for the vines, and of placing the sashes, &c.

f,f,f,

The sort of valvular shutters before described may be seen at f‚ƒ‚ƒ‚. in Fig. 3, and the situation of a wire cloth to exclude tempests and insects at g, g. The opening, h, looking into the back shed of temperate air, does not require this sort of protection. In winter these wire cloths might be covered with woollen netting, by which means Mr. Kewley's regulator might be allowed to open not only the valves.communicating with the back shed, but even the others, at all seasons of the year.

In this figure the outer curtain is contained in a slated box serving as coping to the back wall; by observing the section of which it will readily be conceived how the one breadth of curtain will overlap the other when let down.

This house is supposed to be heated by steam with smoke flues in

the back wall, merely to exhaust in the brickwork a part of what heat may escape from the boiler, and thus to temperate the reserve air in the back shed.

Metallic sashes. One of the greatest improvements in this department of execution consists in the adoption of metallic bars or astragals, instead of the cumbrous wooden ones used when hothouses were first introduced. Adanson is the earliest author who recommends them (in 1763), and they have been occasionally used in this country since, and even before Adanson's time, but chiefly since 1783'. The principal metals used are iron, copper, and pewter.

Cast iron astragals and frames are in use for windows of manufactories and private houses, but from their weight and clumsiness are much less suitable for hothouses than those of wrought iron. Wrought iron astragals are commonly made in two parts, the moulding and hoop, or in architectural language the band and astragal (see a and b, Fig. 7, PL. X.). These are then hammered together, and make a very neat and durable bar or astragal. I have succeeded in getting them drawn in one solid body through moulds, which renders them stronger, better adapted for curved work, and, there being less labour, somewhat cheaper3. Tinning such astragals is of course a great improvement, and should never be neglected where perfection is aimed at.

Wrought iron hoops or bands, tinned and soldered to astragals or other mouldings of pewter, or any such composition of tin and lead in which brass or zinc forms a small proportion, form very light and durable bars, and which are not liable to rust, at least on the

1 Mr. Playfair of Howland-street, engineer, in 1783; Mr. Underwood, plumber and glazier, in 1782; and Mr. Nash, glazier, about the same time,—were chiefly instrumental in their introduction. Mr. Nash used copper, Mr. Underwood pewter on iron hoops and wires, and Mr. Playfair any ductile metal according to circumstances.

2

Chiefly used by Mr. Cruikshanks, sash-manufacturer, Gerrard-street.

For the advantages of this astragal see page 35. Astragal and bar I use synonymously

* Repertory of Arts, vol. vii.

Chiefly used by Messrs. Doyle, Underwood, and Co. Holborn.

inner surface of the sash (see a and b, Fig. 8, PL. X.). From the difference, however, between the expansive powers of the iron rabbet or band and the pewter moulding, change of temperature may occasion their twisting, and even effect their separation; to prevent which the hoop should be burnt in (as the term is), the edge to which the moulding is to be attached being previously serrated and beat back, and a proper mould formed, into which it may be fixed upright, and the melted metal run in (see Fig. 9, a, b, c, and d, PL. X.).

Astragals or bars of sheet copper drawn through moulds to different patterns have been long in use, and among others by Playfair and Nash already mentioned'. For straight work, and especially for upright glass, they form a very neat astragal; but they are unsuitable for curved work, and in any form are more expensive than either iron or composition bars, having at the same time the additional disadvantage of producing verdigrise through any accidental neglect of painting, and the presence of carbonic acid gas or ammonia. For this reason they should at all events never be used in hotbed frames, where both these gases rise abundantly from the dung, bark, or other putrescent matters. Of course the very idea of danger is ridiculed, and the circumstance of any families having been injured by copper stoutly denied, by the tradesmen who manufacture articles from this metalo. Astragals wholly of pewter or other composition, cast or drawn

'At present Mr. Timmins and Mr. Jorden, both of Birmingham, are the principal manufacturers of copper bars and sashes.

A new source of danger to life appears to have been introduced by modern refinement. A Bath paper recently announced the death of Mrs. A. Parnell, aged 56, from eating cucumbers raised by sheet copper reflectors. She died in about three hours after eating of them. It is probable that these cucumbers became strongly impregnated with oxide (subcarbonate) of copper, from the moisture with which the plates must be always covered, being charged with the oxide (subcarbonate) of this metal, formed by the action of the oxygen and the carbonic acid of the atmosphere on the plates; and then falling on and being absorbed by the plants beneath. -Lond. Med. Repository, vol. iv. p. 255.

through moulds, or formed of brass, eldorado metal, &c. are more adapted for shop fronts and church windows than for hothouses.

The frames of sashes where they are not to slide may be made of metal, either of hollow copper or hollow iron, or of cast iron, or by wrought iron drawn to the form of Fig. 6, PL. X, and tinned, which is the description of styles and rails I purpose using for the hinged sashes in curved roofs.

Fitting in the astragals to the outer frames may seem so simple a process as not to deserve mentioning. But when the frames are of wood it is of the utmost importance. The common and I may say universal mode is to rabbet the styles, and insert the ends of the astragals in the top and bottom bar; the consequence of which is, that one grand advantage of metallic astragals, the durability of hothouse sashes, is as completely lost as if the whole sash were made of wood; and the greater number of copper and iron houses which have been erected within these few years at an increased expense with the bearing rafters and outer frames of wood, and the astragals only of metal, will not be found more durable, ceteris paribus, than the less costly, though certainly less elegant houses in the old style, and formed of wood alone. The reason is as follows.

Wooden sash-frames generally decay first at the angles where they are framed together by tenon and mortise: when decay takes place there, it matters not whether they are fitted in with metallic or wooden astragals, as the whole sash must be taken to pieces and renewed. It is true that in theory the metallic astragals may be fitted or inserted in a new wooden frame, but in practice the thing is never done. Much of the glass is destroyed in unglazing, and the astragals are generally broken off at the ends so as to become too short for a new frame. This is particularly the case with frames filled in with copper astragals, which are generally let into notches; but less so

As described by Mr. Timmins in his Specification already referred to.

with the iron astragals of Mr. Cruikshanks and Messrs. Doyle and Underwood, which are generally screwed to the frames'.

The method which I have used extensively, and which I should recommend in every case, is as follows:-Instead of rabbeting the sash, apply a half metallic bar with rabbet and half moulding to each of the two sides and top rail of the sash, and an entire moulding or small bar of iron to the bottom rail. These being fitted to the inside of the wooden frame, are then to be taken out and riveted together, thus forming a metallic frame, to which the astragals and bearing bars are to be riveted. This metallic frame so filled in is then to be screwed to the wooden frame. Of course, when the latter rots, the former, by unscrewing from six to ten screws, can be taken out with the glass entire, and placed within a new frame of wood at a mere trifle of expense. In this way, one set of astragals may endure against three or four sets of wooden frames. The convenience of carriage also, though a trifling advantage, deserves to be mentioned; for these inner frames, occupying so little room, may be made of any shape, and sent glazed or unglazed to the most distant parts of the empire. A proprietor in a remote district may thus choose his design from his gardener or some book, employ his own carpenter to make the rough or plainest work, and get his sashes, which form the grand article of difficulty and expense, from a source where he can calculate on receiving tradesman-like goods.

The mouldings of astragals have been varied, not only according to taste or fancy, but for purposes of utility.

Fig. 10, PL. X. is a section of what Mr. Jorden calls his water escape bar.

Fig. 11 is one which I have used for hotbed lights, made of three tinned hoops riveted together.

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This may be seen in three frames procured from Messrs. Jorden, Cruikshanks, and Doyle and Co. made in 1816, and forming part of the variety of patterns which compose the greenhouse at Bayswater before mentioned.

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