Cyanides, qualitative test for

Alkali or alkaline-earth salts of both complexes are soluble in water (except for Ba2[Fe(CN)6]) but are insoluble in alcohol. The salts of hexakiscyanoferrate(4—) are yellow and those of hexakiscyanoferrate(3—) are mby red. A large variety of complexes arise when one or more cations of the alkali or alkaline-earth salts is replaced by a complex cation, a representative metal, or a transition metal. Many salts have commercial applications, although the majority of industrial production of iron cyanide complexes is of iron blues such as Prussian Blue, used as pigments (see PIGMENTS, inorganic). Many transition-metal salts of [Fe(CN) J4"" have characteristic colors. Addition of [Fe(CN)6]4 to an unknown metal salt solution has been used as a qualitative test for those transition metals. 

The iron salts of ferro and ferricyanic acid are the compounds to which the names cyanogen and cyanide are due. Two of these salts are of deep blue color and the Greek word from which cyanogen and cyanide are derived is cyanos which means blue. The ferric ferro-cyanide, Fe4 "(Fe"(CN6)3, is known as Prussian blue and the ferrous ferri-cyanide, Fe3"(Fe" (CN)6)2, is Turnbull s blue. These compounds are formed when ferric salts in solution are treated with potassium ferro-cyanide and when ferrous salts in solution are treated with potassium ferricyanide. They are common qualitative tests for the two forms of iron salts. The compounds are also used as laundry blueing and are formed in the blue print process of photography. 

With ferric salts in solution either of these reagents forms the cherry red ferric thio-cyanate and is the basis of qualitative tests for iron and the use of the thio-cyanate as an indicator in volumetric titrations. Potassium thio-cyanate may be prepared by heating potassium cyanide with sulphur or ammonium sulphide. Ammonium thio-cyanate may be prepared by heating together carbon disulphide and ammonia in the presence of alcohol. 

In running the DIN 53436 method hydrocarbon and hydrogen cyanide has only been determined qualitatively. The cyanide concentration has been determined four times during the 30 minute steady state combustion process. From these experiments the average concentration of emission has been estimated. The other results presented in Table V from DIN 53436 experiments have been measured in similar ways as for the other small scale test methods. It may be observed that the amount of material burnt in each experiment is smaller than in previous test procedures. The results presented are average values of two deteminations of each material. 

The tests conducted by the institute were qualitative, not quantitative, analyses. In other words, they could only determine whether or not cyanide was present, not how much of it was there. As to whether or not homicidal gassing with hydrogen cyanide took place in Auschwitz, these analyses are worthless, for three reasons ... 

For qualitative (presence-absence) or semiquantitative determinations of cyanide, the easiest and most reliable method is a simple test with either Feigl-Anger or sodium picrate paper. The reactions on which these tests are based as well as other methods for detection of cyanogenic glycosides are described by Hegnauer (1986). 

Vibrationally exciting hydrogen cyanide accelerates its reactions with H, O, or Cl substantially, qualitatively the same result as with water. The energetics for the hydrogen atom abstraction reaction are very similar to each other and to those for water, as Fig. 4 shows. We use two diagnostics to test the spectator picture in reactions of HCN with the different atoms. One is the reactivity of different states as seen in the action spectrum compared to the photoacoustic spectrum. The other is the product state distributions. We find that the extent to which the nonreacting bond is a spectator depends on the identity of the attacking atom. Reactions with Cl atoms are much further from the simple spectator picture than those with H or O atoms. 

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