Carpenters and Masons, Frankford EL Construction, 1913
Looks like carpenters in front and bricklayers working in back.
The building in the background is the "The American Preserve Company Established 1868". The building under construction is the Power House on Beach Street. It would use steam turbine generators to produce AC power (13,200 volts at 25 cycles) to be sent to the Substations throughout the city where it would be converted to 600 volt DC to be used by the trains.
This set contains 39, 8x10 inch glass negatives of the construction of the Philadelphia, Frankford Street Elevated Railroad in 1913. There are also several enlargements of areas that I found interesting. They were packed in a box and separated with paper with notes recorded on them. The paper had disintegrated and stuck to the emulsion side of the negatives. You will find many of the photos with this paper still stuck to the plates because I did not try to remove it for fear of damaging the photos.