Ballast tube No. 110, trade name "Duresite" made by Worldbestoscorp.  Also known as D-110, this tube is rated at 30V, 1.1A, and is intended for use in the primary circuit of a radio-set power transformer operating from the 110-120V AC line.  

Tube has an engraved base that reads:

Duresite

No. 110 Ballast

Worldbestoscorp

Made in USA

Tube is in good used condition, and appears operational.  Cold resistance is about 8.4 ohms.