DETERMINATION OF IRON AND COPPER IN 18th AND 19th CENTURY BOOKS BY FLAMELESS ATOMIC ABSORPTION SPECTROSCOPY
Lucia C. Tang
Previously, foxing of old papers has been associated with action of biological organisms such as molds, and with the presence of iron in the paper. Storage in a damp environment is also believed to contribute to foxing. Certainly, iron is suspect. Almost all papers contain small amounts of iron, and some have an appreciable content. The color of foxing (yellow, brown, or red-brown) suggests iron. Read, Eade and Slingsby2 mention that ferric ions cause an immediate darkening of pulp and also accelerate brightness reversion. Iron in paper is not uniformly distributed. Since the invention of the papermaker's beater in Holland, particles of iron have been regularly struck off the bedplate and carried along with the fiber to lodge in the sheet. The center of a foxed spot sometimes shows a tiny particle of iron oxide.
Not all investigators agree that iron is the cause of foxing. Press3 examined 91 samples of paper using X-ray fluorescence spectroscopic methods and a spectrophotofluorometer and concluded: “Although the amount of foxing was not independent of iron concentration, the relationship was inverse rather than positive.” Press, Iiams,4 Iiams and Beckwith,5 Beckwith, Swanson and Iiams,6 and Baynes-Cope,7 agree that mold plays a major role in the production of the spots. Mold can often be cultured from foxed spots, and fluorescence, usually indicating the presence of a mold-produced color, can be seen when the spots are illuminated with ultraviolet light.
The effect of high humidity in producing foxing has been taken to indicate that it is produced by molds, since molds grow and proliferate at humidities above 70%. On the other hand, cellulose is directly oxidized catalytically in the presence of iron, copper and cobalt compounds, and the reaction is most rapid at high humidities.8
Koenigs9 gave evidence that some fungi employ an H2O2 and Fe++ system to attack cellulose. He also stated, “Peroxide and Fe++ caused large losses in strength and rapidly depolymerized cotton threads at low weight losses; they also increased the swelling and alkali solubility of residual cellulose … the same treatment increased the susceptibility of residual cellulose to the active enzyme preparation.”
Beckwith, Swanson and Iiams6 state that the color change caused by foxing almost invariably means degradation of the paper at the spot. They wrote, “We noted that the foxed paper disintegrated in the acid solution much more rapidly than did the unaffected paper.” Iiams and Beckwith5 reported lower tensile strength in foxed areas, on p. 418.
Previously, the iron and copper content in paper has been determined by colorimetric methods,10,11,12 X-ray fluorescence,13,14,15,16 neutron activation analysis,17,18,19,20 and flame atomic absorption spectrophotometry.2,21,22,23,24 These methods for determining the trace metal content of paper are limited since large amounts of samples are required. With the advent of flameless atomic absorption spectrophotometric techniques, quite small samples of paper can be analyzed.
Using this equipment, it proved possible in the present investigation to analyze the individual foxed spots and determine the metal content as compared to the unspotted areas of the paper. One limitation of the investigation should be pointed out. While the presence of iron and copper can be established by the methods used, these methods do not give information as to whether the metal is in a catalytic form.