J O U R N a L of T H E American Chemical Society

Although numerous articles concerning phosphate chemistry have regularly been appearing in the literature for the last one hundred years, there is as yet no consistent and universally accepted concept of the structure of many condensed phosphates. Until rather recently, in fact, the whole field of phosphate chemistry was in a chaotic state, For example, a given crystalline compound was variously known as the mono-, diand trimetaphosphate. Now, however, the joint application of X-ray diffraction studies, careful microscopic techniques and systematic thermal analyses have led to a rather full concept of the constitution of many crystalline phosphates.2 It can probably be stated safely that continued study along these lines will satisfactorily clarify the remaining problems concerning the crystalline phosphates. On the other hand, many phosphate compositions exhibit a pronounced tendency to form glasses upon the cooling of their melts, and viscid or even fluid masses upon the addition of precipitating agents to their aqueous solutions. Although many of these amorphous materials have been found to have useful properties,s little progress has been made in the fundamental study and interpretations of their properties. It is the purpose of this series of papers to report data which can be used in conjunction with the informa* Present address: Great Lakes Carbon Corporation, Morton Grove, Illinois. (1) A resume of the information dealing with pH titration8 of phosphates given in Papers I and IV of this series was presented by Van Wazer at the 111th Meeting of the American Chemical Society (Division of Physical Inorganic Chemistry) April, 1947. (2) Quimby, Chcm. Rev., 40, 141 (1947). (3) Of 300 U. S. patents on condensed phosphates issued from 1900 to 1947, approximately SO% are primarily concerned with amorphous compositions. tion already published to evolve theoretically sound structural representations of the various condensed phosphates, including the amorphous compositions, and to incorporate phosphate chemistry into the generally accepted picture of inorganic chemistry. In this paper published X-ray data and a pH titration study of various phosphoric acids are used to show that only certain of the many conceivable arrangements of phosphorus and oxygen are to be found in phosphate ions which are relatively stable in aqueous solution. Principles of Structure