Company Names, addresses, dates¹:
  Roberts Manufacturing Co, 408 Princess, Alexandria (1924-1930)
  Roberts Manufacturing Co, 109 King, Alexandria (1932-1947+)
  Roberts Bottling Co, 109 King, Alexandria (?-1950-?)

Notes:
The Roberts Manufacturing Co was at 408 Princess street, the same address as the former Rammel Mfg Co. I'm not sure if the Roberts and Rammel companies were somehow connected.
Roberts Mfg Co was listed in the 1928 "Business, Manufacturers Merchants and Tradesman Financial condition for Alexandria VA" as having an estimated Pecuniary Rating of $3000-$5000.
The 1947 phone book lists "Roberts Manufacturing Co", and the 1950 phone book lists "Roberts Bottling Co". I don't have any phone books in between, so I don't know exactly when they changed the name. The next phone book I have after 1950 is from 1954, and it did not list "Roberts Bottling Co", so I don't know exactly what year they went out of business, but the Frostie Bottling Comany was at the same address (109 King Street) starting in 1958.

Bottles:

(enlarge)	This is an 8" clear crown top bottle embossed: front: Roberts Mfg. Co. / 7 FLUID OZS back: Alexandria, Va. / 25 B6 bottom: R
(enlarge)	This is a 9" clear crown top bottle embossed: front: ROYAL TREAT / TRADE MARK / ROBERTS MFG CO back: ROYAL TREAT / REGISTERED / ALEXANDRIA, VA. bottom: CONTENTS 7 FLU OZS

(enlarge)

This is a modern photo (taken July 2010) of 109 King Street, which used to house the Roberts Manufacturing Company. 109 King is on the left side, where the POPS ICE CREAM sign is.