Investigators of the dental defect known as mottled enamel seem to agree on two points: the defect occurs in certain geographical areas, and the causal factors seem to be associated with the water supply of those areas. Reference to the complete bibliography" on the subject compiled by Kempf and McKay show that no specific common characteristic of the waters from affected areas has been discovered. Following the publication referred to above, A. W. Petrey of this laboratory spectrographically discovered the presence of fluorides in deep well water from Bauxite, Arkansas. These deep wells were formerly the source of water used by individuals who show the characteristic dental defect known as mottled enamel. Several months prior to the investigation covered in the report of Kempf and ;VlcKay the deep well supply at Bauxite was abandoned in favor of another supply which has since been found to be free from fluorides.The presence of fluorides was first revealed by means of the spectrograph. Substances containing both calcium and fluoride show a characteristic spectral band having its head at 5291A and which is degraded towards the infra red end of the spectrum. The spectrum obtained from Bauxite deep well water is shown in figure 1. The definite and specific character of the 5291A band of calcium fluoride is shown in figure 2 which shows the spectra obtainable from a variety of calcium salts. Only those salts which contain both calcium and fluoride show the characteristic band indicated by the limiting lines in the cases of the spectra of calcium fluoride and that of a mixture of calcium oxide and aluminum fluoride.Following the discovery of fluorides in Bauxite deep well water, the author secured samples of water from other localities where the defect occurs. These localities were Colorado Springs, Colorado, a well near Kidder, South Dakota, a well near Lidgerwood, North I Published by the courtesy of Industrial and Engineering Chemistry.

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Fluorine may be titrated quantitatively with thorium nitrate (0.1 N) in an aqueous solution, instead of the 48 per cent ethyl alcohol solution recommended by Willard and Winter (4), by closely controlling the pH of the solution to be titrated. A pH of from 2.9 to 3.1 was found to be suitable, and is obtained by the use of monochloroacetic acid, half neutralized by sodium hydroxide. The end point is more definite in an aqueous solution than in a 48 per cent ethyl alcohol solution. When using a 48 per cent alcoholic solution and 0.1 N tho-

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SINCEthe discovery that fluorine is a causal factor of the dental defect known as mottled enamel on teeth, the literature of analytical chemistry has abounded with papers describing methods for its determination in small amountsthat is, up to a few parts per million. More recently the increased use of fluorides as insecticides has stimulated interest in' such methods and, since the U. S. Food and Drug