The substance in the brass lamplighter stick was Calcium carbide, which was not sold to youngsters! At the end of his round, the Leerie would open the container, and tip the remnants on a stank, gulley or grating. Keen observers would quickly follow, and scrape some of the substance into a dry tin. Next day, a little could be dropped into an adversary's ink-well, whereupon, it would froth and foam over the top of the desk! The gas, which burned safely with a little flame ( as in miner's lamps) was acetylene.
I, too, am from Harriet street, and was amazed to find references to it, having been bulldozed so long ago! I was born in 69, my father was born in 85. Harriet Street, no more!