This 1870’s ad for the Lowell Gas Light Company is a pretty good example of how the meaning of words may change over time. In this case, the product advertized was a by-product of the coal gasification process that yielded the illuminating gas that was used to light the city’s streets, mills and houses for more than a half century. Prodigious amounts of coal were heated in a closed container, the chemical structure changed, releasing flammable gas that was stored and then funneled through underground mains throughout the city. Left behind was a very pure, clean burning solid called “coke” that was used for heating and cooking.