Count Wilhelm Albrecht von Rautter, a naturalized American who was spying on his adoptive country for his native Germany, ran out of his good secret ink and had to use urine. Sympathetic inks are solutions of chemicals that are colorless when dry but that react to form a visible compound when treated with another chemical, called the reagent. For example, when a spy writes in iron sulfate, nothing will be visible until it is painted over with a solution of potassium cyanate, when the two chemicals will combine to form ferric ferrocyanide, or Prussian blue, a particularly lovely hue. The colorless writing of lead sub-acetate will turn into a visible brown compound when moistened with sodium sulfhydrate. Copper sulfate can be developed with ammonia fumes, and it may have been this chemical that was used for the secret writing on the handkerchief of George Dasch, leader of the eight Nazi spies who landed by submarine on Long Island in 1942 to
testing by the industry (Sofos and Smith tested in vitro on removed whole beef hides 1998). The aim of chemical dehairing is to inoculated with E. coli O157:H7 and remove hair, mud, manure, other extraneous Salmonella, Carlson et al. (2008b) found that matter, and associated microbial contami- deluging with SS (6.2%, 30°C) or potassium nants from animal hides before their removal cyanate (PC; 2.4%, 30°C) reduced E. coli from carcasses. Applications (in vitro) of O157:H7 by 4.8–5.1 log10 CFU/cm2 and chemical dehairing on artificially inoculated Salmonella by 0.7 (PC) and 4.2 (SS) log10 bovine hide samples suggested that treatment CFU/cm2. with 10% sodium sulfide (SS) for 16 seconds Physical separation of the dehairing could achieve >3 log cfu/cm2 reductions of process from the hide removal operations inoculated E. coli O157:H7, Salmonella spp
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