F. Mercuric chloride solution, 5:10020 parts
Sodium oxalate solution, 3:10040 parts
Gum arabic in powder24 parts
Glycerine2 parts

Dissolve as said above.

SENSITIZING SOLUTIONS.
FOR BLACK TONES.
Platinite solution, 1:65 parts
Solution E6 parts
Solution C2 parts
FOR SEPIA TONES.
Platinite solution, 1:65 parts
Solution C4 parts
Solution F4 parts

Mix just before use. The solutions do not keep. The paper prepared by either one of these two processes can be exposed as in the old process, and the image developed bythe hot oxalate solution.

The preparation of wood, canvas, etc., for the platinotype printing need not to be described; it suggests itself.

CAUSES OF FAILURES.

The images are veiled.

This defect may result from various causes, viz.:

1st. The stock ferric oxalate solution is impaired by a partial reduction of the ferric salt into ferrous oxalate. The solution should be preserved in an orange colored vial, and kept in the closet of the dark room. It should be tested from time to time for the ferrous salt with a solution of potassium ferricyanate. If it does not contain any ferrous oxalate it can be used by adding to it a little of the iron chlorate solution.
2d. The paper has been exposed to light during the sensi­tizing or the subsequent operations. One should bear in mind that the platinum paper is twice more sensitive than silvered paper.
3d. The sensitized paper has been dried at a temperature above 40 deg. C. (104. deg. Fahr.)
4th. Over-exposure.