From these four illustrations the principle of the raised rear vent is easily understood. The opening of the vent into the fixture is above the water line, and the course of the vent from the opening into the vent chamber is upward throughout. As gases and odors are generated in the use of the fixture their easiest path of escape is through this raised rear vent into the vent chamber, and thence to the outer air. Into this vent chamber each water-closet of a battery is vented. Experience shows conclusively that-hot only does the raised rear vent ventilate the fixture to which it is attached but it acts most satisfactorily as a ventilation for the entire room. So fully is this fact acknowledged that the State of Massachusetts now requires all public toilet rooms to be ventilated in this manner.

There has been a widespread attempt in all parts of the country to overcome the foul odors of large toilet rooms by the use of disinfecting and deodorizing devices, but this is by no means a proper solution of the difficulty, and furthermore, those rooms in which such devices are used have an atmosphere almost as repulsive as that of a room in which no attempt at caring for the odors has been made. The expense of constructing ventilating flues and ducts is small in comparison with the results obtained. If provision is made for such flues and ducts when the building is first planned, the additional expense will be very slight indeed, and not to be considered when the advantages to be gained are taken into account. There is a great variety of methods in which the ventilation system may be installed. Fig. 170, for instance, shows a common method of running a galvanized iron duct back of the partition against which the water-closets stand, thus concealing the work entirely. In Fig. 171 is shown another common and excellent method applicable to a single or double line of water-closets.

Figs. 168-169. - Raised Rear Vent Applied to Washout and Washdown WaterClosets.

Fig. 170. - Local Ventilation by Means of Raised Rear Vent Water-Closets.

Fig. 171. - End View of Local Vent System for Double Line of Water-Closets.

The vent chamber runs the entire length of the line of fixtures, and into it the raised rear vent of each fixture is connected. From the top of the vent chamber a pipe is carried to the flue which is to be used for ventilation. An excellent feature of Fig. 171 is that the vent chamber may be used also as a utility chamber. Its convenience in this respect may be seen from the fact that the supply pipes, flushing valves, and the back venting for the double line of fixtures may be located in this chamber, entirely concealed from view. When so used, a door should be cut into the chamber, to allow entrance for repairs. In Fig. 172, which represents such a toilet room as might be found in a comfort station, a method slightly different is shown. In this instance, there being no flue built into the walls, a galvanized iron flue is carried through the roof, and into it the vent pipes from the two vent chambers are connected.

Fig. 172. - Local Ventilation for Comfort Station or Similar Toilet Building.

A ventilator at the top of the flue will add greatly to the effectiveness of the system. It used to be considered that unless local vent pipes could be connected to a heated flue they could not be effective.

This is no longer considered true, although if they can be so connected the results will be so much the better. Many toilet rooms are now provided with local ventilation in which it is impossible to use a heated flue, but this does not prevent excellent results being obtained from a flue or duct carried through the roof as in Fig. 172. In this case, however, as much assistance as possible should be given by the use of a ventilator, an electric fan placed in the flue, or a gas jet so placed. Local ventilation may be provided in old buildings as well as in new ones, the only difference being that in old buildings the piping must often be exposed to view. However, when properly installed, such ducts are by no means unsightly. The writer recalls an old-time building in which local ventilation has recently been installed with results entirely satisfactory. The toilet rooms in this building are without natural light and without communication with the outer air, conditions under which results are generally most difficult to obtain. In this instance the pipes had to be installed exposed to view. There was no heated flue at hand, and the ducts were consequently run through the roof with a ventilator at the outer end. Such excellent results as are obtained under these poor conditions speak well for local ventilation and for water-closets with raised rear vents.

Fig. 173. - Local Ventilation for Toilet Rooms, Including Ventilation of Urinals.

As previously stated, local ventilation may be applied with splendid results to urinals as well as to water-closets. A system of local ventilation in which urinal ventilation is provided is shown in Fig. 173. This method of ventilation has been in use for some little time and is worthy of far greater use than it has yet obtained. Both architects and plumbers would do well to talk it and recommend its use more generally.