30 Wells and Johnston — Ammonium- Lead Halides. 



solving lead chloride in ammonium chloride solutions and by 

 the use of the corresponding bromides. On repeating his ex- 

 periments with the bromides, we have not observed anything 

 which did not correspond to the salts which we have described, 

 or to mixtures of these with ammonium bromide. He de- 

 scribes his product 4PbCl 2 .22NH 4 C1.7H 2 as an abundant pre- 

 cipitate of very brilliant plates with a pearly luster. We have 

 often observed this beautiful precipitate, but, after many 

 attempts, we have been unable to determine its composition 

 with certainty. It apparently forms only in warm solutions 

 which are almost saturated with ammonium chloride. The 

 prismatic salt NH 4 Pb 2 Cl 5 is usually deposited just before the 

 plates begin to form, and it often forms with them. Large 

 amounts of ammonium chloride often crystallized out when 

 attempts were made to separate the precipitate from the mother- 

 liquor. This happened often even when the solution with the 

 suspended precipitate was poured upon a large mass of filter- 

 paper, so as to soak up the liquid as quickly as possible. Such 

 a crop, which was granular and showed little evidence of being 

 composed of plates, gave 30 50 per cent of lead. By collecting 

 the precipitates, in the manner just described, at an earlier 

 period in the process of their formation, we succeeded in obtain- 

 ing crops that were apparently pure, but the plates were so 

 exceedingly thin and small, and the mother-liquor was so con- 

 centrated, that we had little confidence in the purity of these 

 products. Two such crops gave 51*13 and 53*69 per cent of 

 lead. The formula (NH 4 ) 2 PbCl 4 requires 53*77, and it is pos- 

 sible that this may be the true formula for the substance. It 

 is certain that these two products were practically free from 

 the prismatic salt NH 4 Pb 2 Cl 5 , so that it can be positively stated 

 that the ratio of ammonium to lead cannot be greater than 2 : 1 

 in this compound. Andre's formula is, therefore, very far from 

 correct. He must have analyzed a mixture of the plates with 

 ammonium chloride. We have found all such mixtures to be 

 anhydrous after being dried in the air for a short time, hence 

 the water in Andre's formula is remarkable. 



A number of attempts were made to obtain the compound 

 in a purer state by warming the solutions and by diluting them 

 slightly, after the precipitates had formed, but these operations 

 left the products open to suspicion, since it was found that 

 further dilution completely decomposed the plates. Several 

 crops, made in this way, gave 59-01, 57*64, 53*69 and 57*80 per 

 cent of lead, which is an insufficient amount for the 1 : 1 anhy- 

 drous salt, requiring 624. This may be its composition, but 

 it is possible also that it is a dimorphous form of NH 4 Pb 2 Cl 6 , 

 for the plates, in being square with diagonal markings, resemble 

 the salt KPb 2 Br 5 and other bromides of this type. The unde- 



