COVERING GLASS ROOFS, 



1. Vegetable or mineral pitch, applied hot 

 with a brush, the canvass being spread evenly 

 on a level floor. 



- 2. Linseed oil, boiled with litharge or sugar 

 of lead, or what is called drying oil. 



3. The same oil, holding in solution a small 

 quantity of caoutchouc. 



4. A solution of glue or isinglassj introduced 

 into a stuff, and then acted upon by a clear in- 

 fusion of galls : the fibres get thus impregnated 

 with an insoluble, impermeable, pulverulent 

 lather. 



5. A solution of soap, worked into cloth, 

 and decomposed in it by the action of a solu- 

 tion of alum : whence results a mixture of 

 acid, fats, and alumina, which insinuates itself 

 among all the woolly filaments, fills their inter- 

 stices, and prevents the passage of water. 



6. A varnish made by dissolving caoutchouc 

 in rectified petroleum or naphtha, applied be- 

 tween two surfaces of cloth, as described under 

 Mackintosh's patent. — Vres Diet, of Arts, &c. 



Burnettised canvass — that is, canvass 

 prepared by being saturated with a dilute 

 solution of chloride of zinc — is flexible, and 

 being in pieces of any size, is convenient 

 for covering both pits and houses. The 

 high character given of its durability by 

 many of the most scientific men of the 

 day — (vide Prospectus and Testimonials, 

 published by Sir William Burnett, the 

 patentee, King William Street, London) 

 — has induced us to use it pretty largely. 

 Our experience of it has not extended 

 over a sufficient period to enable us to 

 speak to its durability; but so far as 

 regards the convenience of using it, we 

 think it the very best material we know 

 of for covering glass roofs upon the 

 rolling-up principle. 



The following mode of applying canvass 

 coverings to the roofs of either lean-to or 

 span-roofed hothouses, as a protection dur- 

 ing winter, is the same as that proposed for 

 shading during summer. The covering- 

 material in the former case should be 

 strong waterproof canvass ; while in the 

 latter it should be thin canvass of a semi- 

 transparent fabric. Fig. 790 represents a 



Fig. 790. 



simple apparatus, used at one period in the 

 gardens at Sion House for the latter pur- 

 poses. It was the invention, we believe, of 

 Mr Forrest. Our figure and description 

 are from " The Suburban Horticulturist :" 

 " The canvass is fixed to a roller of wood 50 

 or 60 feet in length — the length depending 

 on the diameter of the pole or rod a, and 

 the toughness of the timber employed, as 

 well as the dimensions and strength of 

 all the other parts. On one end of 

 this rod, and not on both, as is usual, a 

 racket-wheel, b, is fixed, with a plate 

 against it, c, so as to form a pulley groove, 



d, between, to which a cord is fastened ; 

 and about three inches farther on the 

 rod is fixed a third iron wheel, about 6 

 inches in diameter and half an inch thick, 



e, This last wheel runs in an iron groove, 



f, which extends along the end rafter, or 

 end wall of the roof to be covered. The 

 canvass being sewed together of a suffi- 

 cient size to cover the roof, one side of it 

 is nailed to a slip of wood placed against 

 the back wall — that is, along the upper 

 end of the sashes. The other side is 

 nailed to the rod a. When the canvass 

 is rolled up, it is held in its place, under a 

 coping g, by a racket h ; and when it is 

 to be let down, the cord i of the roller is 

 loosened with one hand, and the racket- 

 cord k pulled with the other, when the 

 canvass unrolls with its own weight. 

 The process of pulling it up again need 

 not be described. The most valuable 

 part of the plan is, that the roll of can- 

 vass, throughout its whole length, winds 

 up and lets down without a single wrinkle, 

 notwithstanding the pulley- wheel is only 

 at one end. This is owing to the weight 

 of the rod, and its equal diameter through- 

 out." 



A more simple plan is that adopted 

 for orchid-houses, one of which we have 

 in operation here. It consists of a pole 

 70 feet in length and 3 inches in diame- 

 ter, having fixed to one end a wooden 

 wheel 18 inches in diameter, and hol- 

 lowed out in the periphery — over which 

 a double line is wound, being fixed at 

 one end to the wheel ; the other is 

 brought down and made fast to the front 

 of the house. When loosened, the pole 

 runs down, bringing with it the thin 

 canvass shading which is fastened to it, 

 along its whole length, by one of its sides ; 

 while the other side of the canvass is 



