The perforations in the bottom of the top box not being sufficient to carry off all the water, it gradually fills up that compartment and the pivoted box, thus weighted, is depressed, and the water from the faucets flows into the other compartment and the operation is repeated. The frequency of this rocking movement is easily regulated by the amount of water that flows from the faucet. The operation is not only entirely automatic, but very thorough in its action, as the prints lying upon each other are separated and the upper ones float whenever that end is depressed into the water. The water constantly flowing in and out of the lower box readily eliminates the chemicals that are to be washed out of the prints. So far as he knows, the author originated this method for washing blueprints and photograph prints, and used it with much satisfaction. The boxes may be made of wood and kept well painted; or may be of galvanized iron or zinc protected by paint. The original one was made of white pine, the lower box of 1¬-inch, the pivoted box of ⅞-inch and the top one of «-inch stuff, and painted with white lead.

Fig. 105. Large Blueprint Frame.

Fig. 106. Automatic Washer for Blueprints.

Fig. 107. Longitudinal Section of Automatic Washer.

For drying blueprints various devices have been used, but so far as the author knows, nothing is more economical or better adapted to the purpose than the drying case or cabinet, shown in Fig. 108. The plan is to attach the blueprints to small, round sticks by means of small wooden spring clips and hang them on supporting brackets. The brackets are of light cast iron or wood, as may be preferred, and should incline on an angle of 45 degrees so that any print may be conveniently reached and removed without removing those in front of it. Two pairs of these brackets are located, one above the other, for medium sized prints, say 18 × 24 inches, as on the left of the engraving, or one pair for large prints, as shown on the right. The upper section of prints drip the water into a zinc tray supported by a wooden shelf fixed at an angle of 45 degrees, from the lower corner of which, at the back a short pipe carries the water into a similar tray resting on the floor, and from which suitable pipes carry the water to the waste pipes coming from the print-washing apparatus. The drying of blueprints may, of course be hastened by the application of artificial heat. For Purpose doors may be added to the drying case and a small steam coil be placed in the bottom or near the back of the case. But to use artificial heat, or any temperature over about 100 degrees, has a tendency to cause the prints to be distorted by unequal shrinkage, and marred by wrinkles, while drying them by the natural temperature of the room and suspended as in this case, will cause them to come out in good condition.

Fig. 108. Blueprint Drying Racks and Cabinet.

In some large establishments blueprints are made by exposing the blueprint paper and tracing to the action of the light from an electric arc lamp located within a metallic cylinder, in which the paper is fixed, and by means of which excellent blueprints may be made in large numbers without the aid of sunlight. While the first cost is considerable the work is done very expeditiously and economically, as the cost of labor is very much reduced. The quality of the work is good, as the lighting is very uniformly distributed over the surface of the sensitized paper.

To adapt this plan of construction and equipping a drawing room to the wants of larger establishments requiring a larger force of draftsmen it is only necessary to extend its length so as to provide for a greater number of the single and double drawing tables, to any extent required. The capacity for filing drawings, tracings, and blueprints should be increased in proportion. One or more large tables for reference drawings will be needed, and the number of lockers increased to accommodate the added force of draftsmen. Otherwise the same arrangement of the plan need not be disturbed, as the chief's room, photographic dark room, vault, and all the other accessories will be either ample or very easily adapted to an increase to any reasonable extent that may be desired.