24 PHOTOGRAPHIC FACTS AND FORMULAS 
Orange Middle 614 
End 585 
Yellow Middle 559 
End 534 
Green Middle 512 
End 491 
Cyan blue Middle 473 
i End 455 
Indigo Middle 439 
End 424 
Violet Middle 409 
End 396 
Lavender Middle 384 
End 372 
ORTHOCHROMATISING PLATES.—Ordinary, or non-colour 
sensitive plates, may be orthochromatised by bathing in solu- 
tions of dyes. As a rule, such plates have a higher colour 
sensitivity than those coated with an emulsion to which the 
dye is added during the mixing, but they do not keep quite 
as well. . 
Blue-green and Green Sensitisers—Acridine orange NO, 
made by Leonhardt of Mithlheim, was the old dye used. A 
saturated alcoholic solution was made and diluted with water ; 
but this dye stains the gelatine so tenaciously that it cannot 
be removed except with an alcohol bath. It has been entirely 
replaced by pinaflavol (Hoechst) or the new dye dimethyl- 
styrylpyridine methiodide, suggested by Mills and Pope. This 
is used in an aqueous solution, 1:30,000 or 1:40,000, in 
which the plates are bathed for 3 minutes, rinsed and dried. 
This gives very even sensitiveness from the bright blue to the 
yellow at 560, then falling off rapidly to 620, and without the 
usual gap in the blue-green, characteristic of the eosine dyes. 
Green and Yellow Sensitisers—Erythrosine is the dye 
