306 WINDOWS AND SKYLIGHTS 



glass with box frames and sash, and 9 cents for S. S. glass with plank 

 frames and sash. In 1900 skylights cost from 23 to 30 cents per square 

 foot with D. S. glass. Windows are commonly estimated at 25 cents 

 per square foot and skylights at from 40 to 50 cents per square foot 

 in making preliminary estimates. 



The American Luxfer Prism Company manufacture sheet prisms 

 for factory purposes that can be cut to fit any opening up to 36" x 84". 

 The cost of sheet prisms to fit ordinary windows is about 40 cents 

 per square foot. The improved skylight prisms made by this company 

 cost about $i . 50 per square foot. 



TRANSLUCENT FABRIC. Translucent fabric consists of a 

 wire cloth imbedded in a translucent, impervious, elastic material, prob- 

 ably made of linseed oil. The fabric may be bent double without cracking 

 and is so elastic that changes due to temperature or vibrations do not af- 

 fect it. If a sheet of translucent fabric is suspended and a fire applied to 

 the edge, it will burn up leaving a carbonaceous covering on the wire. 

 But if the edges are protected it will burn only with great difficulty. 

 Live coals falling on skylights of this material will char and burn holes 

 but will not set fire to the fabric. It is therefore practically fireproof. 



Translucent fabric will not transmit as much light as glass, but 

 makes a most excellent substitute therefore. It shuts off sufficient 

 light so that the lighting is uniform throughout the shop and makes it 

 possible for men to work directly under it without shading. Where 

 one-quarter of the roof is covered with the fabric the lighting is prac- 

 tically perfect. The fabric should be washed with castile soap and 

 warm water occasionally, and should be varnished every year or two 

 with a special varnish furnished by the manufacturers. It is said to 

 become less opaque with age. When properly cared for the fabric 

 has been known to give good service for ten years. The fabric is man- 

 ufactured in sheets 3' 3" wide and in lengths from 4' 6" to 9' o". 

 The framework for translucent fabric is the best made of wood. A 

 standard frame for sheets 3' 3" x 6' 3" is shown in Fig. 151. The fab- 

 ric must be stretched tight and carefully nailed around the edges of 

 the sheet. The capped joint with metal cap shown in Fig. 151 is very 



