Wonderful research, John and Susan!
While looking for that - I found the list for POW's at West's Buildings Hospital which lists Powell as a POW/Nurse -
I cut out the portion related to Powell -
It states: "L. T. Powell, Private, 2nd Florida, Company I, captured Gettysburg, PA,
July 4th, (to be exchanged at City Point, VA - [currently Hopewell, VA - about 30 minutes south of Richmond, VA] for POW exchange or transfer to another Northern prison camp?!?) escaped September 8, 1863."
This is somewhat puzzling. Other military records at the National Archives state that Powell was captured on July 3rd, 1863. And what is with the "exchange?" Why wasn't he simply shipped from Baltimore to another prison camp? More mystery.....