BAXTER AND JONES. — ATOMIC WEIGHT OF PHOSPHORUS. 147 



appreciably settled. Since the coagulation of the precipitate seems 

 to occur much more readily in the presence of excess of silver, a 

 considerable amount of silver nitrate in solution was added. The 

 precipitate coagulated and settled immediately. It was washed and 

 dried as usual. This sample was somewhat darker in color than the 

 other samples and gave a large amount of insoluble residue when 

 treated with dilute nitric acid. The analysis showed that it contained 

 about two hundredths per cent too much silver. This method of 

 preparation is evidently unsatisfactory. 



Three unsuccessful attempts were made to prepare silver phosphate 

 from trisodium phosphate. The samples obtained in this way did not 

 appear homogeneous after being dried and contained considerable 

 sodium in spite of protracted washing. Two of these samples were 

 found by analysis to contain, respectively, 4.4 and 4.1 per cent less 

 silver than pure trisilver phosphate. The third of these samples 

 was so unsatisfactory in appearance and in its behavior during its 

 preparation that it was not analyzed. This method of preparing 

 silver phosphate is evidently not suitable for our purpose. Time was 

 lacking to investigate further this anomalous behavior. 



Method of Analysis. 



Unfortunately, owing to the high melting point of silver phosphate, 

 it was not feasible to fuse the silver phosphate before its analysis in 

 order completely to eliminate all water. Instead it was heated in a 

 platinum boat, in a current of pure dry air, at a temperature of about 

 400° for seven hours, and then by means of bottling apparatus 23 it 

 was inclosed in its weighing bottle without coming in contact with the 

 moist air of the laboratory. During this heating the access of light to 

 the sample was prevented. The continuous current of air which passed 

 over the silver phosphate during the heating was driven by a water 

 pump successively through an Emmerling tower containing beads 

 moistened with silver nitrate solution, through a tower containing 

 small pieces of fused caustic potash, then through three towers con- 

 taining beads drenched with concentrated sulphuric acid, and finally 

 through a long tube containing phosphorus pentoxide which had been 

 resublimed in a current of air. The hard glass tube containing the 

 platinum boat was surrounded by blocks of aluminum 24 which were 

 jacketed with asbestos on the top and sides and heated directly from 



23 Richards and Parker, These Proceedings, 1896, 32, 59. 



24 Baxter and Coffin, These Proceedings, 1909, 44, 184. 



