Wells and Johnston^ Ammonium- Lead Halides. 27 



obtained. These results show that the ammonium-lead halides 

 are entirely analogous to the potassium salts, and that there is 

 no indication that they are governed by a law of their own. 



Returning to the mixtures described as compounds by 

 Andre, it should be noticed that he came near finding the cor- 

 rect formulae for three salts. His formula 4PbCl 2 2NH 4 C1. 

 6H 2 would be correct if the water were omitted. He should 

 have found two more molecules of NH 4 Br in the formula 

 7PbBr 2 .l2NTI 4 Br.7H 2 in order to have the salt (NH 4 ) 2 PbBr 4 . 

 H 2 0, and his formula 3PbBr 2 .2NH 4 Br.H 2 0, in comparison with 

 the errors involved in his more complicated mixtures, is rather 

 near NH 4 Pb 2 Br 5 . 



Such work as Andre's is liable to hinder the development of 

 correct chemical theories. A case has been mentioned above 

 where it is probable that his results have been an important 

 factor in causing the ammonium double halides to be looked 

 upon as a class of bodies distinct from the alkali-metal com- 

 pounds, and it may be mentioned that Carnegie* has used 

 Andre's formula PbBr 2 .6NH 4 Br in support of a theory on double 

 halides, although, as must be added, he considers Andre's 

 more complicated formulae as inconsistent with his ideas. 



We have investigated the ammonium-lead halides by methods 

 which are entirely like those used for the potassium salts, and, 

 in addition, numerous experiments have been made in order 

 to investigate Andre's methods of preparation. The analytical 

 methods used have been simple. Ammonium was determined 

 by distillation with potash solution and alkalimetry. Lead was 

 determined by treating the substance in a platinum crucible 

 with sulphuric acid, evaporating, igniting and weighing lead 

 sulphate. To determine a halogen, the substance was treated 

 with hot water and an excess of silver nitrate was added ; after 

 sufficient digestion, nitric acid was added, and when the pre- 

 cipitate had settled properly it was collected and weighed on 

 a Gooch filter. Water was determined by the loss at 100°, or 

 sometimes at a somewhat higher temperature. 



1:1 Ammonium-Lead Chloride, SNB^PhClyHfi :— This 

 is formed by dissolving lead chloride in hot concentrated solu- 

 tions of ammonium chloride and cooling. Sample A was made 

 by dissolving 25 g of PbCl 2 in 700 cc of an ammonium chloride 

 solution which was more than saturated when cold. The' 

 double salt was deposited in the form of colorless, transparent, 

 prismatic crystals while the solution was still somewhat warm. 

 Some of the crystals were removed from the warm solution, 

 quickly pressed between smooth filter-papers and air-dried for 

 analysis. On cooling the solution, ammonium chloride crystal- 

 lized upon the double salt. Sample B was obtained by dissolv- 



*Am. Chera. Jour., xv, 11. 



