Victor Appleton 
Tom Swift Omnibus #4: Tom Swift and His Electric Rifle, Tom Swift in the City of Gold, Tom Swift and His Air Glider [EPUB ebook] 

Tom Swift Omnibus #4 contains a trio of stories: In the tenth of Victor Appleton’s original Tom Swift novels, Tom goes hunting for ivory in Africa, and encounters an adventurer who is trying to rescue a captured missionary team. In the eleventh of Victor Appleton’s original Tom Swift novels, Tom once goes hunting for Mexican treasure, supposedly protected by a tribe of head hunters. In the twelfth of Victor Appleton’s original Tom Swift novels, Tom ventures to Russia in search of platinum.