From the 1940's on metre gauge was phased out except on this interurban line, which by then only ran these types of cars from the 1920's called "tanks". They were the first bogie units, the first full metal units, and some of the largest trams ever to run in Barcelona. There were also standard-gauge units of the same type, and eventually the metre gauge units were converted to standard gauge as the metre gauge line shrank.
From the 40's on, services where something like: 70 was the full line to Badalona, 71 partial interurban service to Sant Adrià, (these two lines used two trams coupled back so as to be bi-directional, and at their Barcelona terminus they ended on a stub track), then line 41 ran on a branch line to Pueblo Nuevo, a borough of Barcelona (now called Poblenou), and line 42 was another partial service on the same line as lines 70 and 71 which ran to the San Martín (now Sant Martí) borough. The difference in numbers were because urban and interurban services. For some time 70 and 71 used this green livery, while 41 and 42 used a red livery like the urban trams (which were eventually also painted in a turquise green like in the initial photographs).
All of this just to explain that this tram, running on line 42, was a partial service of line 70 (by this time the 41's branch was gone, and line 71 didn't exist).
It's hard to tell where the pic was taken but I'm quite sure it's here:
https://www.google.es/maps/@41.3908626,2.1837945,3a,75y,246.03h,84.13t/data=!3m6!1e1!3m4!1sqviGd2Sf2J-VGrcw0DnYnA!2e0!7i13312!8i6656The building behind the tram is barely visible, but from the structure right below the roof I'm quite sure it's that old building that's still there.
Note the mixed gauge on the other track, but not where the tram is running. Std gauge tram ran on this street but only in one direction, in the other on a different street.
