Some science behind the scenes
Kendal Black Drop
Kendal Black Drop was a medicine based on opium used to relieve pain. Quite a number of people in the 19th century used it thinking it was a pain reliever [which it was], only to get hooked – Samuel Taylor Coleridge was one of them, Lord Byron appears to be another.
It was based on opium with sugar, vinegar and spices such as nutmeg and cinnamon.
It is possible to make a kind of toffee using sugar, vinegar and spices - my father used to make ‘bonfire toffee’ [as he called it] for use on Guy Fawkes day using brown sugar, golden syrup or treacle, vinegar and a little butter. I hasten to add there was no opium in it, but as you can see the result would have been a toffee, very appealing to children, but with opium in it. This was why kendal black drop was given to children. The vinegar might have helped dissolve the opium.
This would result in an ‘opium sweetie’ in ‘suckable’ form – so portable and easily dose controllable.
As entirely pointless note for those interested, my father’s recipe for the toffee was half a pound of butter, half a pound of treacle or golden syrup, half a pound of brown sugar, all boiled together until it starts to set on a cool plate. Then add about 2 to 3 tablespoons of malt vinegar [this make it less sickly sweet and helps it to set]. It was then poured into little oiled sweet size patty tins or else we used it to make toffee apples.