Saw this at the hardware store and couldn't resist: Dr. Brown's cream soda, from a company dating to 1869! Now all the other characters just need their own sodas, too. Honestly, ever since we got our gasogene last Christmas I've been pondering what various characters' favorite flavors would be… (Scroll down to see my brainstorming ideas, as well as links to primary sources from the 19th-century about sodas.)
My historical fiction series: http://www.thisvictorianlife.com/historical-fiction.html
Unflavored sparkling mineral water for Silas. The original purpose of gasogenes was to mimic the naturally occurring sparkling water found in various mineral springs. (Mineral water —both sparkling and still) has been used as a health tonic for thousands of years. In the 1880s recipe books for soda making included instructions on what to add to soda to mimic the waters of various famous spas.
A couple historic books on soda:
The Standard Manual of Soda and Other Beverages by A. Emile Hiss: http://tinyurl.com/zbvonjp
A Treatise on Beverages or The Complete Practical Bottler Full Instructions for Laboratory Work by Charles Herman Sulz: http://tinyurl.com/h455nv2
Sarsparilla for Nurse McCoy and her Appalachian kin
Cherry phosphate for Jacob, and violet for Addie.
Source for acid phosphate drops: Extinct Chemical Company http://www.artofdrink.com/shop
Rose for Kitty
Coconut lime for Capt. Kellam
Blood orange phosphate for Felix