Johnson, M.D. (1984) Documentation and quality assurance of the computer files of historical water chemistry data from the Wisconsin Northern Highland Lake District (the Birge and Juday data).Wisconsin DNR Technical Report.Methods not included in Johnson (1984):Nitrite Nitrogen- Sulphanilic acid procedure. Standard methods for the examination of water and sewage, Pub. Health Assn., New York, 5th edition, 1923, 13. Other Documentation: Domogalla, B.P., Juday, C., and Peterson, W.H. 1925. The forms of nitrogen found in certain lake waters. Jour. Biol. Chem. 63: 269-285.Ferric Ion- First calculated by subtracting ferrous ion from total iron measurements. Standard methods of water analysis. 1936. Amer. Pub. Health Assoc. P. 309. New York. Procedure was modified to determine ferric ion by acidifying samples by adding 1 milliliter of 3 N HCL to 50mL of lake water. With the iron samples in readiness, add 5 ml of the thiocyanate solution to the sample and to the standards, mix and compare immediately. (Standard Methods, Amer. Public Health Assoc. 8th ed., p. 75, 1936). Other documentation: Domogalla, B.P., Juday, C., and Peterson, W.H. 1925. The forms of nitrogen found in certain lake waters. Jour. Biol. Chem. 63: 269-285.Ferrous Ion- First calculated by ferricyanide method. Procedure was modified to determine ferrous ion by subtracting ferric ion from total iron. Documentation: Domogalla, B.P., Juday, C., and Peterson, W.H. 1925. The forms of nitrogen found in certain lake waters. Jour. Biol. Chem. 63: 269-285.Manganese- Determined by the persulfate method using the procedure described in Standard Methods of Water Analysis, Amer. Public Health Assoc., p. 84, 1936.Chlorophyll-a- A photometric method was used, in which the color of the light was confined to the wave-length 6200-6800 A which are absorbed by chlorophyll. Water samples of 5 to 15 liters (18 liters in the case of very low plankton content) were taken from different depths by using a hand operated vacuum pump), the water was the centrifuged at 25,000 rpm (for about 30 minutes). Residue was then washed with 98percent acetone, and CaCO3 was added to neutralize organic acids. This residue-acetone mixture was ground to extract the chlorophyll. The acetone extract was then filtered through filter paper into a flask, the residue being thoroughly washed with pure acetone. The light absorption of the extract was then measured. Procedure was carried out in a single day, under minimal light. Documentation: Kemmerer, G.I., and Hallett, L.T. 1938. Amount and distribution of the chlorophyll in some lakes of northeastern Wisconsin. Trans. Wisconsin Acad. Sci. 31: 411-438.Phosphate- Ceruleomolybdic method employed. Documentation: Juday, C., Birge, E.A., Kemmerer, G.I., Robinson, R.J. 1927. Phosphorus content of lake waters of northeastern Wisconsin. Trans. Wisconsin. Acad. Sci. 23: 233-248. Other Documentation: Robinson, R.J., Kemmerer, G.I. 1930. Determination of organic phosphorus in lake waters. Trans. Wisconsin. Acad. Sci. 25: 117-121.Redox Potential- Determined in situ on a given sampling date by use of a bright platinum electrode. Eh readings were made in millivolts. Documentation: Allgeier, R.J., Hafford, B.C., and Juday, C. 1941. Oxidation-reduction potentials and pH of lake waters and lake sediments. Trans. Wisconsin Acad. Sci. 33: 115-133.Note: The methodology used to determine copper, alumnium, boron, and hydrogen sulfide could not be determined.