The canvas is hung up to dry; but as sometime must elapse before this particular piece will be ready for sensitizing, we proceed with another canvas which is fit and proper for that process.  The room, we should have mentioned, is provided with windows of yellow glass; but as there is plenty of light nevertheless, the fact hardly strikes one on entering.  The sensitizing, with a solution of nitrate of silver, is conducted with a glass rod in the same way as before, the solution being thus compounded: 

Nitrate of silver........................ 4 parts. 
Citric acid.............................. 1 part. 
Water.................................. 140 parts.

Again the canvas is dried, and then comes its exposure.

This is done in a room adjoining.  We lift a curtain and enter a space that reminds one of the underground regions of a theater.  There are curtained partitions and wooden structures on every hand; dark murky corners combined with brilliant illumination.  Messrs. Winter use the electric light for enlarging, a lamp of Siemens’ driven by a six-horse power engine.  The lamp is outside the enlarging room, and three large lenses, or condensers, on three sides of the light, permit the making of three enlargements at one end at the same time. (See Fig.)

[Illustration]

The condenser collects the rays, and these shine into a camera arrangement in which the small negative is contained.  The enlarged image is then projected, magic lantern fashion, upon the screen, to which is fastened the sensitized canvas.  The screen in question is upon a tramway—­there are three tramways and three screens in all, as shown in our sketch—­and for this reason it is easy to advance and retire the canvas, for the purpose of properly focusing it.

Even with the electric light now employed, it is necessary to expose a considerable time to secure a vigorous impression.  From ten minutes to half an hour is the usual period, determined by the assistant, whose experienced eye is the only guide.  We should estimate the distance of the cameras from the enlarging apparatus to be about fourteen or fifteen feet in the instance we saw, and when the canvas was taken down, a distinct outline of the image was visible on its surface.

By the way, we ought to mention that the canvas is in a decidedly limp state during these operations.  It has just sufficient stiffness to keep smooth on the screen, and that is all; the treatment it has received appears to have imparted no increase of substance to it.  Again it is brought into the red-brick washing apartment, and again treated in one of the white enameled baths as before.  This time it is the developer that is contained in the bath, and the small limp tablecloth—­for that is what it looks like—­after being drawn over the glass rod, is put back into the bath, and the developing solution rocked to and fro over it.  The whiteness of the bath lining assists one in forming a judgment of the image as it now gradually develops and grows stronger.  Here is the formula of the developer: