This investigation was undertaken primarily with the purpose of studying the applicability and value of concentrated hydriodic acid as a general reagent for the detection and separation of insolubles. The principal results of this work are recorded in the first tow parts of this dissertation. In addition, there was developed a special method for the quantitative volatilization of stannic oxide form various mixture by the use of ammonium iodide. This is described in third part. The author wishes to express his sincere gratitude to Professor Earle R. Caley for suggesting the experiments here recorded, and for his constant advice interest during the course of the work. Thanks are due also to Professor N. Howell Furman for his kind criticism.