This description of the carbro chemical reactions is not completely accurate as its fails to account for the function of dichromate - (and whether DAS #3 could be used in place of dichromate was questioned).
The Basic Carbro Chemical actions:
1. The ferricyanide and bromide react on the silver image, resulting in the formation of silver bromide and potassium ferrocyanide.
2. The water soluble potassium ferrocyanide passes into the carbon tissue and reduces the dichromate in the carbon tissue - it is this reduction of dichromate in the presence of gelatin that results in the insolubilization of the gelatin.
See Charles Lighton's discussion in the August, 1927 Photographic Journal for a more complete description.