This little tidbit from history was sent to me from Mark Dallmeyer, which I was able to track down:

The first soda dispenser in New York City was an aged
negro, Ben Austen, better known as “Old Ben,” who was
born a slave on the plantation of a Mr. Austen in North
Carolina. He was given his freedom at his master’s death and
came to New York and was married in 1836. In 1838 he
had his first experience in the soda-water business with John
Matthews. The elder Matthews at that time was established
at 55 Gold street, where he manufactured soda-water appara-
tus. Soon afterwards he undertook to make soda water with a
wooden generator, a gasometer and a pump. The gas passed
from the generator into the gasometer and was thence pumped
to the fountain. Two or three gasometerfuls was the foun-
tain charge, and “Old Ben’s” thumb applied to the fountain
cock was safety valve and pressure gauge alike. If the thumb
could hold its own against the pressure, more gas was pumped
into the fountain; if the thumb was forced from the open
cock, it was decided that the pressure was at least 150 pounds,
and the fountain was deemed charged.
“Old Ben” used to supply the city customers, and he began,
in 1839, the delivery of soda water to the Matthews clients.
As the business grew, an engine was installed and “Old Ben”
was made the fireman. Later he was again promoted and
put into the machine shop, where he used to assemble iron
fountains and coat the inside with paraffin. There is no
doubt that John Matthews obtained his idea of the pressure
gauge and safety cap for generators from “Old Ben’s’ thumb,
hence the space devoted to this ex-slave.
Such were the first uncertain steps of this typical American
“infant industry.”

Furthermore, as reported by American Heritage Magazine:

During the Civil War draft riots, when angry Irish mobs roamed the New York streets seeking to hang any Negro they could find, Matthews was obliged to ship Ben out to safety in a packing case, as though he were a tank of the product.