In the 1900s, something and some thing were used interchangeably, and today (for the most part) are still used interchangeably. If you used some thing instead of something, most people would never give it a second thought. However, as this article explains, some thing is not a correct way to spell something. In fact, some thing means something entirely different.
From the article:
Something is a pronoun. Something means an unspecified object or concept. It is a common word in both spoken and written English.
They explain that unlike other pronouns like it and they, something doesn't refer to anything specific.
Concerning some thing:
Some writers divide the pronoun something into two words, forming the phrase some thing. This is not an accepted variant of this word. Something is a compound, and should always be spelled as a single word.
Some thing (in present-day English) would refer to some specific thing. as the article explains:
That’s not to say that there are no contexts where some and thing might appear next to each other as separate words. Some is a determiner, and thing is a noun. The phrase 'some thing took hold of his ankle' would not feel out of place in certain 19th century horror fiction.
Today, though, a horror writer would probably include an adjective, to form 'some terrible thing' or 'some unholy thing'. Most people would also simply use the pronoun something.
So to sum up: in the 1900's, some thing and something were synonymous. Nowadays, some thing only refers to some specific thing, giving it a much more literal connotation.