Large list of books, the ones from 1925 and before often full text and copyright free.

Sample technique for finding travel in Open Library:

1) Select ebook books
2) search terms: Malaya travel
3) scan list for appropriate dates and icon that says "Read online"
4) Open "Read Online"
5) In "Search this book" Enter the keyword you really want to see
for instance: opium

Little pins will show up for each instance of your word and you can hover over the pin to see the word in context. The more pins in the book, the more your term appears!