Cover the surface evenly with the following solution, using such a brush
as is generally employed for the letter-press: 1 part soluble citrate of
iron (or citrate of iron and ammonia), 1 part red prussiate of potash,
and dissolve in 10 parts of water.

The solution must be kept carefully protected from light, and better
results are obtained by not mixing the ingredients until immediately
required. After being coated with the solution, the paper must be laid
away to dry in a dark place, and must be shielded entirely from light
until used. When dry, the paper is of a yellow and bronze color. After
exposure the surface becomes darker, with the lines of the tracing still
darker. Upon washing, the characteristic blue tint appears, with the
lines of the tracing in vivid contrast. Excellent results have been
obtained from glass negatives by this process.--_Proc. Eng. Club,
Phila._

* * * * *




REPRODUCTION OF DRAWINGS IN BLUE LINES ON WHITE GROUND.

A.H. HAIG.


The following process for making photographic copies of drawings in blue
lines on white background was invented by H. Pellet, and is based on the
property of perchloride of iron of being converted into protochloride on
exposure to light. Prussiate of potash when brought into contact with