CHAPTER XXIII. 

 WINDOWS AND SKYLIGHTS. 



Glazing. For glazing windows and skylights, two substances, 

 glass and translucent fabric are in common use. 



GLASS. The principal kinds of glass used in windows and sky- 

 lights are (i) plane or sheet glass ; (2) rough plate or hammered glass ; 

 (3) ribbed or corrugated glass; (4) maze glass; (5) wire glass glass 

 with wire netting pressed into it ; (6) ribbed wire glass ; and (7) prisms. 



(1) Plane Glass. Plane or common window glass is technically 

 known as sheet or cylinder glass. It is made by dipping a tube in molten 

 glass and blowing the glass into a cylinder, which is then cut and 

 pressed out flat. Without regard to quality sheet glass is divided ac- 

 cording to thickness into "single strength" and "double strength" glass. 

 Double strength glass is ^-inch thick while single strength glass is 

 about i-i6-inch thick. In mill buildings, lights larger than 12" x 14" 

 are usually made of double strength glass. With reference to quality 

 sheet glass is divided into three grades A A, A, and B. The A A is the 

 best quality, the A is good quality while the B is very poor. The B 

 grade is suitable only for stables, cellars, etc. For residences, offices, 

 and similar purposes nothing poorer than AA should be specified. The 

 A grade does very well for ordinary mills, although the A A grade 

 should be used if practicable. 



(2) Plate Glass. Plate glass is made by casting and not by 

 blowing, and is finished by grinding and polishing on both sides until 

 a smooth surface is obtained. It is usually y or 3-16 inches thick. 

 The price depends upon the size of the plate and the quality of the glass. 

 The rough plate glass used in mills is not finished as carefully as for 

 glass fronts, and it may contain many flaws that would not be allow- 



