'Valuable flame spectra', early 20th century.

Four dry plate negatives showing spectra asociated with the work of Walter Hartley (1846-1913). In 1883 Hartley established that relationships exist between the wavelengths in the spectrum of an element and its position in the periodic table. The gelatin dry collodion proces replaced the wet collodion proces in photography, which in turn had replaced the calotype and daguerreotype. In 1871, Richard Maddox pioneered the dry plate, discovering that if gelatine mixed with silver bromide was spread on glas, it stayed sensitive to light after drying.