Napthol Red, the napthol pigments were first patented in 1911 and used initially as cotton dyes, then in the 1920's they were 'laked' (precipitating a dye with a metallic salt to stabilize it) and began to appear as artist's colours.
This is basically a luminous 'primary' red which leans towards orange, semi-transparent and like most of these more modern pigments is cleaner than the cadmiums.
It will function well as the mixing red on the palette with excellent tinting power, and like all Langridges colour has a very high pigment load which means a tube of this will go a long way.
Below is a video of this exact colour being milled at Langridge.
Pigment - PR112, Monoazo
Vehicle - Linseed Oil, Consistency - Stiff