It has been known for fully 25 years that vitamin D is not stable when mixed with a preparation containing 25% or more of minerals. In 1932, the observation was made that, when mixed with limestone, cod liver oil did not retain its vitamin D.1Cod liver oil was added to ground limestone and the mixture stored in glass jars in the laboratory. When examined two weeks later, the mixture was devoid of the vitamin. With further investigation, researchers found that cod liver oil lost vitamin D rapidly when added to a salt mixture containing all of the mineral elements necessary for growth of the rat. However, the loss was just as rapid when the oil was mixed with a preparation of silica of the same degree of fineness. Loss of vitamin D at temperatures ranging from 85 to 100 F was more rapid than at room temperature, and