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ment is an object', will be very trifling, and consist chiefly of shutters to the openings for ventilation doors, and fittings up for the back sheds. Sometimes also the outer frames of iron sashes are proposed to be formed of wood. In all cases, to promote duration, the wood-work of hothouses should be first fitted together, then taken asunder and painted two or three times with boiling tar. When dry it should be finally put together, and then painted with Le Souff's “anticorrosion,” which after twenty years experience has been found the most durable paint for hothouses?.
The metallic work requires particular care in the execution so as to prevent rust. I have already mentioned a necessary precaution for that purpose (p. 45), and may here add, that where cast iron is to be used as wall plating, or in masses to be inserted in the ground, in walls, or used as tanks or cisterns, the composition with which Mr. Dickenson (inventor of the iron buoys) coats his patent iron casks will be found a desirable addition.
As the weight of cast iron rafters, as hitherto adopted in hothouses, has been an objection to their use, I shall here give some forms which will render them nearly or entirely as light as wood, with all the advantages (and some additional ones) of the heavy rafters of which there are sections in Pl. VIII. Fig. 7.
1. Supposing the rafter intended for a common sloping roof for two tiers of sashes, both to slide, viz. the upper sashes to slide down, and the lower ones to slide up or down at pleasure; then Fig. 1, Pl. IX. will represent a side view of such a rafter as cast, and before it has received the requisite fittings up. It may either be cast in one length, to be screwed together at a, a, or in four lengths, and joined at b,a,b.
Fig. 2 is a side view of the same rafter fitted with rollers, d, d,
· It sometimes happens that an architect in his employer's instructions is forbid to introduce any plan not in use in the neighbourhood, or which does not correspond with a house already erected, &c. &c.; in which case, plans in general use must be resorted to.
• A very good proof of this may be seen in Miller and Sweet's Nursery, Bristol, and in some very neat wooden houses which they have erected at an adjoining villa.
which turn on fixed axles for the sashes to rest on instead of the usual rabbet, and which serve at the same time to lessen the friction when the sashes are in motion. The short cylindrical pieces, c, c, are cast apart, with gudgeons to fit small sockets, which sockets, with the
cylinders fitted in, are screwed to the upper and lower bars of the rafter. The use of these vertical cylinders is to lessen the friction on the sides of the sashes when they are in motion.
Fig. 3 is a view of the same rafter completely fitted up, and with the sashes in their places. e..f is a gutter suspended from the under edge of the rafter, to
collect any water which may' enter in the intersticés between the sashes and raster.' This gutter may be formed of tinned iron, leather, or varnished papier maché; and as it rests on the forked ends of the wire suspenders, g, it may
be taken out and put in at pleasure. h. Transverse rods to retain the rafters on edge and at equal
distances, and also to keep down the sashes. Supposing this rafter to be twenty feet in length, and the bars at an average three quarters of an inch
square, it will weigh one hundred and three quarters, which at the present London prices will cost, including the fittings up, about 21. 108. With regard to the strength of such a rafter, a sufficient number of experiments have not yet been made on cast iron' to admit of a correct estimate; but there can be no doubt of its supporting ten hundred weight, or double the weight of the sashes which would bear on it, even if laid in a horizontal position and unaided by supports at any part between the two ends. By doubling the number of braces its strength will be increased by nearly one third part, and by placing it in an inclined position, like the sloping roof of a hothouse, every one knows that the weight it will bear increases as the cosine of the angle of elevation diminishes. The lightest wooden rafter that could be made to answer the same pur
pose would require eight cubic feet of timber, which with labour at the present London prices would amount to 21. 88., to which must be added the expense of the rollers which would in this case be required for the sashes, the greater first cost of painting, and greater cost annually for repairs. The cast iron rafter would thus be the cheapest at first, the most durable, the most elegant, and it would not throw above one third of the shadow of the other on the glass.
2. Supposing the width of the house the same, and that it were (as in most cases it is) desirable that the one sash should move up, and the other down; then Fig. 4 will represent a side view of such a rafter with the sashes in their places. a. An iron plate, which projects from the bottom rail of the
upper sash over the upper rail of the lower sash, to carry
off the wet. b. A projecting plate, for the same purpose, to throw off the water
at the upper angle of the back wall. c. Transverse rods to fix the rafters and retain the sashes. When
it is desirable to open them further, they can be lifted up and tilted, or taken entirely off. This rafter would be
equally strong, and one fourth cheaper than the other. Mr. Timmins' proposes a very neat mode of forming metallic rafters, by casing plates of cast or wrought iron, with thin copper, which, if it were desirable to continue the old form of rafters, might in many cases be adopted with advantage, the precaution of tinning the copper being duly attended to before introduced in houses where grapes were grown. But curved rafters and convex roof promise so many
Specification of Patent for improvements in hothouses, March 1813. A very elegant house by Mr. Timmins is erected in Mr. Loddige’s Nursery, which in point of lightness and tradesman-like workmanship surpasses any I have seen. Mr. Timmins generally tins his copper. Mr. Jorden, in his patent house erected for public inspection in the Union Nursery, King's Road, has used a light rafter; but as only a small part of the roof of that house is move. able, it became an easy matter to omit superfluous strength. The water escape bars and grooves, in that house are neat and ingenious.
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.
The sort of valvular shutters before described may be seen at f,f,f, 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
. 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
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. .
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.