Company Names, addresses, dates: ¹
  Janney & Co, 145 King Street, Alexandria VA (1867,1870,73,75,76)
  Janney & Co, 152 King Street, Alexandria VA (1881,1883)
  Janney, John H., 701 King Street, Alexandria VA (1897-1899)

Notes:
Janney & Co was Samuel Hopkins Janney (1804-1887)² and his son Mahlon Hopkins Janney (1843-1882)³. In the 1870s, they had both a drugstore and an insurance company in the same building. The Census from both 1870 & 1880 list Samuel as an insurance agent and Mahlon as a druggist, so apparently Mahlon ran the drugstore.
The 1881 City directory lists A.A. Warfield and Charles J.W. Summers as additional proprietors of the drugstore.
Mahlon died under strange circumstances in September of 1882. He took sick, then appeared to have recovered, then went back to work, and then he took strychnine and died.⁴
In 1883, the drugstore was taken over by by A.A. Warfield, who's advertisements described him as the "Successor to Janney & Co".⁵
I have a letter from October 5, 1882, displayed on my Leadbeater page where Edward S. Leadbeater writes that he was helping to price stock from 8 to 10 PM every night at Janney & Co's store. It doesn't indicate why Leadbeater was helping Janney though, but it must have had to do with the fact that Mahlon Janney had just passed away.

In 1897 another Janney drugstore showed up. This one was run by John H. Janney. I can't find any evidence that John was related to Samuel or Mahlon Janney - he just had the same last name.
John Janney was the successor to L. Stabler, whose drugstore was at 701 King Street. Ernest L Allen's drug store was listed at that address from 1900-1918, so presumably he took over John H. Janney's store. Then John Timberman's drug store was at that address from 1919-1950.

Bottles:

	book # 267 (in medicines section) This is a 5.75" aqua-colored bottle, embossed: front: JANNEY & CO. left side: DRUGGISTS right side: ALEXANDRIA, VA.
	book # 268 (in medicines section) This is a 4.75" clear bottle, embossed: vertical: JANNEY & CO. / DRUGGISTS / ALEXANDRIA VA.
	book # 270 (in medicines section) This is a 4.25" clear bottle, weakly embossed: vertical: (mortar & pestle) / JANNEY & CO. (on a ribbon) / "J & Co" (monogram) / ALEX (on a ribbon) / VA. Since the embossing is so week, I included a close-up with different lighting to try to make it stand out.