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CHEMICAL SOIL .ANALYSIS BACKGROUND This report covers the methods and results of the chemical anaiysis of 80 soil samples for the Buckeye Ranch Project in San Joaquin County, California. The samples were collected in the fall of 1992 by Biosystems and submitted for analysis. The chemical changes in the soil resulting from human occupation include substantial increases in nitrogen, calcium, carbon and phosphorus compounds. Cook and Heizer (1965) conducted an in-depth study describing the amounts generated by a hypothetical group of inhabitants. Of the above elements, phosphorus, in the form of phosphates, has proven to be the most reliable of land use by prehistoric populations. This is due to the tendency of phosphate to remain fixed in the soil where deposited, with little horizontal or vertical movement. The use of soil phosphate analysis in investigating archaeological sites was well established in Europe by the late 1930's but it wasn't until 1948 that similar work was conducted in the United States. Even so, the use of phosphate analysis was seldom performed in North America until a simple and relatively fast "spot test" was developed by R.C. Eidt in 1972 (Woods 1975:9-10). PROCEDURES Eighty soil samples were collected from both site and off-site contexts, from an average depth of 10 centimeters below the surface (see Map 11 - in pocket). These samples were chemically analyzed for qualitative phosphate values, soil pH, and carbonates reactions. The color classification of each sample was also determined using the Munsell Soil Color charts. The test for phosphate (PO,)values followed the procedures outlined by Eidt (1973:206-210)and modified by Woods (1975). Two reagents are prepared: Reagent A consists of 30 ml of 6 Normal hydrochloric acid added to 5 g ammonium molybdate dissolved in 100 ml of distilled water. Reagent B is prepared by dissolving .5 g of ascorbic acid in 100 ml of distilled water. The hydrochloric acid in Reagent A releases the phosphates from the soil sample, which form a phosphate molybdate compound by combining with the ammonium molybdate. Reagent B reduces this compound, yielding molybdenum blue. The phosphate values are determined by evaluating the physical characteristics of the chemical reactions in the soil sample. These reactions include the time of appearance and the intensity of the molybdenum blue coloration, length of the rays emanating from the sample, and the extent of the ring surrounding the sample. The samples are assigned values ranging from one (for a negative phosphate reading) to a six, in accordance with the recorded results. It must be noted that this is a subjective test and requires careful interpretation by the analyst. Woods pointed A3-1