Since it has been established that the dental disease in man known as “mottled enamel” is due to the drinking of water containing fluorine, the removal of fluorides by filtration has become an important problem.

I have found that a contact filter 15 cm high, made of river sand passing a screen 60 to the inch, to which has been added 2 per cent. by weight of powdered aluminium, will remove the fluoride from a solution containing 30 parts per million of sodium fluoride. The absence of fluoride in the filtrate was determined by the zirconium-alizarin colorimetic method.

S.P. Kramer
Ft. Thomas, KY.

*Read letter online at https://science.sciencemag.org/content/80/2086/593.1