Detection by indicator papers

Angeli Test(Soggio Angeli in Ital) (Detection of Acidity in NC Propellants). The presence of small amts of acids, which are not easily detectable by indicator papers or by means of tests involving heating may readily be detd by the following procedure ... 

The ammonia produced in the lime test can be detected by indicator papers. Especially effective is filter paper moistened with silver nitrate-manganese nitrate solution. On contact with ammonia, a gray or black fleck appears on the white paper. The stain is due to a mixture of free silver... 

Tetryl or Picrylnitromethylamine(pp 488-89) can be detected by treating(in a micro test tube) a drop of benzenic soln of the sample with powdered manganous sulfate filling the tube to 2/3 of its capacity. After evapg benzene, the tube is immersed (after covering its mouth with a disk of filter paper moistened with Nessler soln) into a bath preheated to 140° and the temp is raised to 150°. A gray or black Stain on the paper appearing within 5 mins indicates the presence of a nitramine, such as tetryl. 

Nitrate in the presence of bromide and iodide The brown ring test for nitrates cannot be applied in the presence of bromides and iodides since the liberation of the free halogen with concentrated sulphuric acid will obscure the brown ring due to the nitrate. The solution is therefore boiled with sodium hydroxide solution until ammonium salts, if present, are completely decomposed powdered Devarda s alloy or aluminium powder (or wire) is then added and the solution gently warmed. The evolution of ammonia, detected by its smell and its action upon mercury(I) nitrate paper (see Section III.38, reaction 1) and upon red litmus paper, indicates the presence of a nitrate. 

Test for ammonium ions Boil a little (c. 0 1 g) of the substance with sodium hydroxide solution. The evolution of ammonia, detected by its odour and its action upon red litmus paper and upon filter paper soaked in mercury nitrate solution, indicates the presence of an ammonium salt. 

If ammonia is evolved, as detected by its action upon red litmus paper or upon mercury(I) nitrate paper, the presence of a nitrate or nitrite is indicated. Nitrite will also be detected in the reaction with dilute sulphuric acid (see test 7) if nitrite is absent, the presence of nitrate is established. 

Two types of traditional sizes, namely starch and glue (protein), can be tested for, and the tests are also used for identification of adhesives on paper artefacts. Starch can be detected by placing a drop of iodine solution onto the area to be tested, and a blue-black colouration reveals the presence of starch. There are many tests for protein, but in the ninhydrin test a solution of ninhydrin in methyl Cellosolve with a trace of surfactant is added to the paper that is then heated in an oven at 100°C. A purplish stain indicates the presence of protein. 

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