e bottom one will act as
a bearer for the floor, and the second one for the developing
bench. Both sides can be put together in this way, and both
exactly alike. Keep the ends of the crosspieces back from the
edges of the boards far enough to allow the end boards to fit in
against them.

One of the narrow sides can be formed in the same way, fixing the
crosspieces on to correspond, and then these three pieces can be
fastened together by screwing the two wide sides on the narrow
one.

Lay the floor next, screwing or nailing the boards to the
crosspieces, and making the last board come even with the ends of
the crosspieces, not even with the boards themselves. The single
boards can then be fixed, one on each side of what will be the
doorway, by screwing to the floor, and to the outside board of the
sides. At the top of the doorway, fix a narrow piece between the
side boards, thus leaving a rectangular opening for the door.

The roof boards may next be put on, nailing them to each other at
the ridge, and to the sides of the room at the outsides and eaves.
They should overhang at the sides and eaves about 2 in., as shown
in Figs. 3 and 4.

One of the sides with the crosspieces in place will be as shown in
Fig. 2 in section, all the crosspieces and bearers intersecting
around the room.

The door is made of the same kind of boards held together with
crosspieces, one of which is fastened so as to fit closely to the
floor when the door is hinged, and act as a trap for the light.
The top crosspiece is also fastened within 1 in. of the top of the
door for the same reason.

Light traps are necessary at the sides and top of the door. That
at the hinged side can be as shown at A, Fig. 5, the closing side
as at B, and the top as at C in the same drawing. These are all in
section and are self-explanatory. In hinging the door, three butt
hinges should be used so as to keep the joint close.

The fittings of the room are as shown sectionally in Fig. 6, but
before fixing these it is best to line the room with heavy, brown
wrapping paper, as an additional safeguard against the entrance of
light.

The developing bench is 18 in. wide, and in the middle an opening,
9 by 11 in., is cut, below which is fixed the sink. It is shown in
detail in Fig. 7, and should be zinc lined.

The zinc should not be cut but folded as shown in Fig. 8, so that
it will fit inside the sink. The bench at each side of the sink
should be fluted (Fig. 9)