Company Names, addresses, dates¹:
  Barq Eastern Bottling Co, 1842 Bladensburg Rd NE, Washington DC (1939-1940)
  Barq's Bottling Co, 1601 5th NW, Washington DC (1948-1951)

Notes:
Wikipedia says that Barq's started in 1890 in New Orleans, Louisiana.

Barq's first shows up in Washington DC directories in 1939, at 1842 Bladensburg Rd. That same address was listed for Samuel Farber and his Whistle bottling company from 1933-1938¹.

Barq's is listed in the 1948 and 1951 directories at 1601 5th Street NW, which is the same address that John Schlueter's Northwest Bottling Company was at from 1890-1933. The Gridiron Club beverage company was at that address from 1936-1941. The Washington Bottling Works Inc was also at that address in 1941¹.

Bottles:

(enlarge)	book # 64 This is a 9.5" clear crown top bottle with raised diamonds on the shoulder, embossed: front: Drink / Barq's / IT'S GOOD back: CONT. 12 FL. OZ. base: BARQ'S BOTTLING CO / 2633 / E T 51 / 1 / WASHINGTON, D.C.
(enlarge)	book # 65 This is an 8.3" clear crown top bottle with some embossing and some white & blue markings: front (ACL): DRINK / Barq's / IT'S GOOD back (embossed): Barq's / REG / CONT. 8 FL. OZ. base: BARQS BOTTLING CO / WASHINGTON DC / 7305 - 1B 53