Analysis of the Halogenated Nitro-compounds

The detection of chloropicrin is most simply carried out by direct sensory perception. 

Various methods have been suggested for the detection of chloropicrin by chemical means. None of these is as sensitive as perception by odour, according to Deckert.  

Method of Pyrogenic Decomposition. One of the most widely used methods for the detection of chloropicrin in air consists in decomposing it by heat and then testing for chlorine in the products. 

The gas mixture is passed through a tube of quartz or porcelain heated almost to redness and the products of the decomposition are then bubbled through a solution containing potassium iodide and starch paste. If chloropicrin is present in the mixture under examination, chlorine will be liberated and this will liberate iodine from the potassium iodide and so colour the starch blue. Engel s Indicator Apparatus is based on a similar principle. It consists of a glass tube (see Fig. 12) through which passes a 

The sensitivity of this reaction depends very much on the age of the starch solution and it is advisable to use a recently prepared solution.  

---