While Van dyke brown and argyrotype use ferric ammonium citrate, the light-sensitive element used for the Kallitype is ferric oxalate.
2.
In a typical procedure, equal volumes of an 8.1 % ( w / v ) solution of potassium ferricyanide and a 20 % solution of ferric ammonium citrate are mixed.
3.
The presence of thiosulfate or ferric ammonium citrate in the medium produces a black precipitate in the presence of H 2 S, allowing " Shigella " which does not produce H 2 S, and appears as green colonies to be distinguished from " Salmonella " which does produce hydrogen sulfide and appears as black colonies.
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