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The diameters themselves could have been used instead of the areas, but in view of the possibility of an occasional irregular spot the areas were considered more trustworthy.The areas so obtained were then compared to those produced by known amounts of barium sulfate, completing the analysis.Examples of spots obtained are given in Figure 2, and representative results are given in Table I, including results obtained in the presence of large amounts of sodium, calcium, magnesium, potassium, and chloride ions. Average areas, corresponding to various weights of precipitates, are shown by the curve in Figure 3. However, for the best results, individual flasks should be calibrated with known amounts of barium sulfate, since with the swirling technic different flasks gave somewhat different areas for the same weight of barium sulfate, particularly with the larger amounts. DiscussionErrors in the method are chiefly due to differences in crystal size and possibly in shape and not to errors in measurement, as good checks could be obtained on the latter for an indefinite number of times with any given sample. The authors believe that the point to watch most carefully in the entire procedure is the first addition of barium chloride solution, since this governs the number of crystal nuclei formed, which in turn governs the number and size of those eventually formed.The solution was boiled down to the volume occupied by the (barium sulfate-saturated) barium chloride solution. In this way any solution of barium sulfate was overcome. Actually there was a small blank, about 0.005 mg., probably