That formula is for a ready to use, one-shot intensifier. It works well. You bleach the negative in the solution and then redevelop in something like Dektol.
Kodak IN-4 chromium intensifier
Water 1 l
Potassium dichromate 90 g
Hydrochloric acid (conc) 64 ml
Dilute 1:10 for use. Bleach negative thoroughly in the above solution. Wash 5 minutes, then redevelop in room light in a non-staining developer without excess sulfite. Degree of intensification may be controlled by degree of redevelopment. After redevelopment, rinse negative, fix, and wash. Repeat process for greater effect.