Steve: I couldn't find anything regarding the use of goat's bile in leather tanning or processing. It is apparently a light yellow-green and I couldn't find anything about using it as a leather dye either.
Animal bile has long been used in traditional Chinese medicine
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4123376/Could Powell have killed goats on site for their hides, then sold the meat and bile? Lots of South Asians in London c. 1800.
Goat bile and guts are used in a SE Asia soup - Papaitan in the Philippines
