22 - 6 Cole: Hexamethylenetetramine (533 



The sensitivity was determined by making the test on solu- 

 tions of decreasing concentration until one was reached which 

 gave no crystals. The concentration was figured in terms of 

 the positive ion; that is, a 1 : 1,000 solution of silver nitrate 



contained 0.1574 g. ( A ^° 3 ) silver nitrate. The most dilute 



solution which gave crystals within about three minutes was 

 taken as the limit of sensitivity. 



TESTS WITH HEXAMETHYLENETETRAMINE 



Sensitivity with hmt, 1 : 1,500. 

 Sensitivity with hmt + KI, 1 : 15,000. 

 When a fragment of hmt is added to a drop of a hydrochloric 

 acid solution of an antimony salt, colorless octahedra and dode- 

 cahedra first appear. Toward the periphery of the drop 

 square-ended prisms exhibiting parallel extinction then appear, 

 gradually entirely replacing the crystals belonging to the iso- 

 metric system. The latter seem to be unstable or soluble in 

 excess of the reagent. 



If no crystals appear, a fragment of potassium iodide is added 

 to the test drop. Yellow octahedra are formed in the presence 

 of antimony. Bismuth and tin also yield yellow octahedra, but 

 the crystals are much smaller. The test should be performed 

 in a solution acidified with hydrochloric acid. Nitric and sul- 

 phuric acids do not interfere. However, any one of these three 

 acids will give colorless crystals in the presence of hmt and potas- 

 sium iodide ; the crystals are more soluble than the yellow octahe- 

 dra formed with antimony, bismuth, or tin and, furthermore, are 

 easily distinguished by form and color and by the fact that they 

 exhibit parallel extinction under crossed nicols (Plate 1, fig. 1, 

 and Plate 2, fig. 12). 



Sensitivity with hmt, 1 : 8,000. 



Sensitivity with hmt + KI, 1 : 100,000. 

 Hexamethylenetetramine forms with bismuth compounds in 

 hydrochloric acid solution large, colorless, highly refractive 

 octahedra and dodecahedra belonging to the isometric system. 

 Bismuth never gives crystals which polarize and may thus be 

 distinguished from antimony (Plate 1, fig. 2). 



