IT has been pointed out by Bruce and Callow1, and again recently by Harrison and Mellanby2, that the rachitogenic property of cereals may be due to the formation of a sparingly soluble salt of phytic acid and calcium. In this laboratory, investigations on the chemical properties of this compound have shown that sodium phytate can only form an insoluble precipitate when an equivalent or an excess of calcium is added. Under such conditions the filtrates are clear and contain only a trace of phytic acid. When less than half the equivalent quantity of calcium is added, no precipitate is formed and the solution remains clear. The calcium in the solution is not precipitated by the addition of phosphate or oxalate. This indicates complex ion formation, and also that the degree of ionization of free calcium is extremely small. When the amount of calcium is between one half and one equivalent the solution is turbid and difficult to filter.