His theory was that when mixed with water, all acids release hydrogen ionns.
Also said alkalis form hydroxide ions in water
Idea worked fairly well, but only for acids & bases that dissolve in water. But ammonia gas cannot react as base even when not dissolved in water, which was one reason why there were ideas weren't immediatly accepted.
Plus, in 1880's when he first suggested molecules ionise in water, many scientists didn't believe it was possible. Charged subatomic particles were yet to be discovered so idea of charged ions seemed peculiar.
Lowry & Bronsted