Wells and Johnston — Ammonium-Lead Ilalides. 31 



termined double chloride can be readily prepared by dissolving 

 160 g of ammonium chloride and 25 g of lead chloride in suffi- 

 cient boiling water to make a volume of 400 ce , and allowing 

 the solution to cool slowly. The compound often forms in 

 such abundance as to completely fill the solution with a loose 

 mass of the very thin plates. 



Andrews other method of preparing his products was by dis- 

 solving lead monoxide in ammonium chloride and bromide 

 solutions. He describes only one complicated bromide, 

 PbBr,.6]^"H 4 Br.H 2 0, made in this way. "We have made a 

 number of experiments with ammonium bromide and lead ox- 

 ide without obtaining anything but our own salts and mixtures. 

 Since a number of his chlorides were made by dissolving lead 

 oxide in ammonium chloride solutions, we have made a very 

 careful study of the products obtained by this operation. 

 Andre sometimes indicates the length of time of boiling the 

 ammonium chloride solution with lead oxide, but is uncertain 

 how rapidly he boiled his solutions. We have therefore made 

 numerous experiments with wide variations in the amount of 

 ammonia boiled off. Among the various products that we 

 obtained, including the salts that we have described, we fre- 

 quently noticed a substance that appeared to be new. It was 

 deposited after the solutions had become cold or nearly so, 

 forming brilliant crystals, apparently nearly cubic in form, but 

 so much rounded as to have no distinct faces. These crystals 

 were often 1 or 2 mm in diameter. They formed upon the bot- 

 tom and sides of the beaker, adhering firmly to the glass, and 

 their quantity was sometimes such that the walls of the vessel 

 were thickly studded with them. This product evidently cor- 

 responded with one of Andre's, for he says of " PbCl 2 .18]^"H 4 

 C1.4H 2 " that it is a very hard crystalline deposit adhering to 

 the glass. We encountered considerable difficulties- in obtain- 

 ing the substance in a pure condition, for it was inclined to 

 deposit upon other things that had previously formed, and it 

 adhered to them as well as to the glass. The first crop analy- 

 zed (Xo. 1) was evidently not pure. Two other crops (2 and 3) 

 appeared better, but stillnot quite pure. At least, by decanting 

 a solution just before these crystals began to form, we obtained 

 a crop (No. 4), that seemed entirely satisfactory. The follow- 

 ing analyses of the four crops were made : 



Ammonium. Lead. Chlorine. 



No, 1, 28*28 13-44 58-05 = 99-77 



Xo. 2, 6-51 



No. 3, 6-74 



N.O. 4, 1-08 



The crystals of the last product had exactly the same appear- 

 ance as the others. It is evident that lead is not an essential 



