We can't tell you a lot about the Casa Tosquella (Ronda General Mitre, 219-225; map), except that it appears to date back to 1906, and was designed by Eduard Balcells i Buigas, one of the less well known Modernista architects. Some of its arches have a Moorish sort of look to them, and the little we could find on the Internet suggests the influence of Belgian art Art Nouveau.
It's very dilapidated and the ironwork is all rust-eaten and it must be starved of restoration funds. Only its protection as a Monumento Artístico, seems to have saved it from being torn down by developers long ago and replaced by yet another ghastly block of apartments.
Listen to the cars thundering by on Barcelona's inner ring road — the Ronda Mitre — which it must predate by a good 50 years, and you'll agree that it's a miracle that it has survived.