Here is the explaination of fruit saltan explanation of fruit salt:
Invented in the 1850s by James Crossley Eno of Newcastle, the Fruit Salt sold like hotcakes to sailors looking for something to keep them healthy on long journeys. The product is still available today – now manufactured by GlaxoSmithKline, it sells in vast quantities worldwide and is a popular ingredient in Indian cookery. It contains sodium bicarbonate, citric acid and sodium carbonate, but in 1906 the Pharmaceutische Centralhalle für Deutschland analysed it as 50% sodium bicarbonate, 15% sodium bitartrate and 35% free tartaric acid.
http://thequackdoctor.com/index.php/enos-fruit-salt/ But do click through the link - it also includes an advertisement for fruit salt from 1890.