Although called a changing box this is a transfer box. It was quite popular and sold for many years. Most sizes up to 10" x 12" were advertised. A 10" x 8" box cost £5.5.0, brass binding was extra.

To load a dark-slide it is slid into the brass fitting on top of the box, part way along the box is a stud which is pushed aside by the dark-slide, this opens the shutter in the box. The face of the dark-slide consists of a hinged panel, this is now released by a catch and springs back a short way which opens the shutter in the dark-slide. The glass plate is now free to fall into the dark-slide, the panel on the dark-slide is then pressed down which closes the shutter making the dark-slide light-tight. The top of the transfer box can be positioned by a tambour arrangement.