1/100 Molecule of the acid is dissolved in the requisite amount of sodium carbonate solution, which is then diluted to 250 c.cs., 25 c.cs. concentrated hydrochloric acid are added and the whole titrated with normal Nitrite solution. The number of c.cs. multiplied by 10 gives the percentage composition. Care must be taken only to spot the nitrite paper, as it is impossible to get accurate results if the paper be stroked with the rod.

Notice should be taken of the fact that very energetic diazonium salts can themselves turn the starch-iodide paper blue rapidly, and it is also essential to know the relative sensitiveness of the paper.

Sulphanilic acid, metanilic acid, and naphthylamine sulphonic acids are diazotized at 15o.

Cleve acids cannot be determined so easily, as they couple up at once with themselves. In this case it is best to add the greater part of the nitrite to the neutral solution and then to acidify, stirring well. Or the solution may be diazotized directly at o°, nitrite being added until the violet coloration first produced changes to a pure brown. The indirect nethod is, however, to be preferred, as it is more rapid.