This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
In Fig. 333 is shown a double-hung window which is in two parts with a mullion between them. The mullion is shown at A. The window shown also has two transom sashes with a mullion between the sashes BB and the mullion at C. The mullions A and C are usually made 8 or 9 inches wide, so as to provide space for the weight boxes in the thickness of the mullion. Fig. 334 shows a section taken horizontally through the mullion A, with spaces for the weights at DD and with a strip E to separate the two weight boxes. FF are the two pulley stiles, made in the usual way as described above, with parting beads at GG and the sashes at HH. K is the piece which forms the outside finish of the mullion and helps to form the enclosed weight boxes, with the pulley stiles grooved into it as shown. The piece L forms the inside finish of the mullion and the inside wall of the weight boxes and may be made very plain or very elaborate to suit the taste of the designer. It may be treated with sinkages or with raised moldings and varied to almost any extent. MM are the stop beads which hold in the sashes and serve also to cover the joint between the pieces FF and the piece L.
Fig. 333. Double-Hung Window in Two Parts with Mullion Between.
In Fig. 335 is shown a casement window with a mullion. The mullion is seen at A. It will be noticed that it is much narrower than the mullion used in the case of the double-hung window shown in Fig. 333, the reason for this being that in the case of the casement window there are no weights to be taken care of and so there need not be any weight boxes in the thickness of the mullion.
Fig. 334. Horizontal Section through Mullion of Fig. 333.
Fig. 335. Casement Window with Mullion.
BB are the casement sashes which are in this case filled with leaded glass. They should be hinged at the sides to open inward or outward stopping against the mullion. In Fig. 336 is shown a section taken horizontally through the mullion A, showing its construction. The sashes are shown at CC and are intended to open out. They are grooved to prevent the rain water from penetrating to the inside and are rabbeted so as to further keep out the weather. The mullion itself is shown at D. It is built up out of three pieces which may be molded to suit the taste, but there must always be a rabbet for the sash to stop against. E is the piece which forms the inside finish of the mullion and FF are the stop beads.