Modern Gasworks Practice

476 MODERN GASWORKS PRACTICE boiling. The bottle is occasionally shaken, and heating is continued until a clear solution is obtained. After cooling the whole of the naphthalene picrate will crystallize out in fine needles. The contents of the bottle are washed into a 250 c.c. measure, and are made up to this volume with. water. The whole is then filtered. One hundred e.c. of filtrate are taken, a few drops of lacmoid solution are added, and the whole is titrated with. decinormal soda solution until the colour changes from a brownish. yellow to a greenish. tint. The 50 c.c, burette supplied with. the apparatus reads off directly the number of grains (uncorrected) of naphthalene per 100 cubic feet of gas. This reading divided by the tabular number gives the corrected valne. If an ordinary burette is used the result may be calculated. as follows:— Two hundred and twenty-nine parts of picric are combined in the picrate with 128 parts of naphthalene, therefore the quantity of picric acid formed multiplied by 128 —— gives the quantity of naphth aline in the volume of gas passed through the meter.