Report of Committee on Standard Methods of Water Analysis to the Laboratory Section of the American Public Health Association Volume 1

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 Excerpt: ...to sulphate of iron is estimated by difference. By determining the amount of ferrous and ferric iron as already described (see pages 47 and 48) the ferrous sulphate and the ferric sulphate may be computed. From the data obtained as above described and from the methods of computation already given, there may be computed the quantities of each kind of acidity, expressed in parts per million of free carbonic acid and of sulphate acidity in terms of SO4,--both for the free sulphuric acid and the sulphates of iron and aluminum. DETERMINATION OF ALUM OR SULPHATE OF ALUMINA. Where these chemicals are used for the coagulation of muddy or highly colored waters, it is essential that care be taken in operating the plant to prevent any of these undecomposed salts appearing in the water after treatment. There are two ways by which a test for their presence is made, one being the measure of acidity of the water when titrated. with such indicators as lacmoid or erythrosine, and the other the so-called "logwood" test. ACIDITY BY LACMOID OR ERYTHROSINE.'8 This determination is made in a corresponding manner to the alkalinity determination already described on page 6. If the reaction is not alkaline, then £g sodium carbonate may be used in measuring the amount of acidity due to the alum or to the sulphate of alumina, and the results expressed in terms of calcium carbonate (or computed into grains of sulphate of alumina per gallon). Lacmoid, phenacetolin or erythrosine may be safely used as indicators for this test. Methyl orange cannot be used, because as already explained it is not reversible, and indicates only on the alkaline side of the neutral point. LOGWOOD TEST.80 This te3t is based upon the fact that solutions of logwood or of hematoxylin in the presen...