Twenty-five c.c. of the naphtha are placed in each of two beakers, and titrated with decinormal acid, using in the one case a few drops of litmus solution, and in the other a solution of methyl-orange, as indicator. With litmus usually 01 to 02 c.c. of decinormal acid is required to neutralise the naphtha. With methyl-orange the total alkalinity should be greater, at least 5 or 6 c.c. of decinormal acid being required for neutralisation. *

The difference of the two results is the "methyl-orange alkalinity." It serves as a measure of the pyridine and amine bases - though of course only an approximate estimation, since there may be more than one basic substance present. It may be expressed in terms of pyridine from the knowledge that 1 c.c. of N/10-acid == 0 008 c.c. pyridine; but in practice is usually given as the volume of decinormal acid required, in the absence of information as to which base is actually predominant.