...The Case of the Illustrious Client, in which super villain Adelbert Gruner gets vitrol in the face...

Thanks. You're right. Charles Augustus Milverton was another arch-villian, a blackmailer actually, and he got his from another wronged woman (who shot him).

Your investigations led me to find http://www.geocities.com/fa1931/british/conandoy/milverto.html.
Apparently the full text of ALL the Sherlock Holmes stories in available on line !