Here’s an old advertisement from the Washington Times. This ad for gas lighting and heating ran in the March 2nd, 1906 newspaper. You could choose to have gas fixtures installed throughout your home and have the entire cost amortized over the course of the year … kind of like the deals Best Buy offers these days (no interest financing for 18 months!).

By the way, the company has been around since it’s founding in 1848. President James K. Polk signed the Congressional act creating the company on July 8th, 1848. The company went on to install gas lights in the House and Senate chambers, followed by the lighting in the White House and down Pennsylvania Avenue.
By 1856, Washington Gas had grown to include nearly 1,700 customers, more than 30 miles of gas mains, and about 500 street lights.
When did east of the river get its first gas light?
I’m not sure … good question
Gas lighting in the early days was notoriously unreliable and dangerous in the early days. Fires and asphyxsiation due to leaking gas were common. This reminds me of Samuel Clemens’ (Mark Twain) famous letter to the Hartford (CT) gas company:
Hartford, February 12, 1891.
Dear Sirs:
Some day you will move me almost to the verge of
irritation by your chuckle-headed Goddamned fashion of shutting your Goddamned
gas off without giving any notice to your Goddamned parishioners. Several times
you have come within an ace of smothering half of this household in their beds
and blowing up the other half by this idiotic, not to say criminal, custom of
yours. And it has happened again today. Haven’t you a telephone?
Ys
S L
Clemens (Mark Twain)