Wells and Johnston — Ammonium- Lead Halides. 33 



Experiments icith Ammonium Choride and Lead, Lodide. 



Poggiale* and Yolkelf have each described a mixed double 

 halide of ammonium and lead, neither of which agrees with 

 the tvpes of unmixed halides which we have described in this 

 article. Poggiale's formula is PbI 9 .4ETH 4 C1.2H a O, while 

 YolkeFs is PbI 2 .3XH 4 Cl. It is evident that the two investi- 

 gators obtained the same compound, for both made their 

 products in essentially the same way, and both describe them 

 as occurring in the form of silky needles. We have repeated 

 the experiment of dissolving lead iodide in ammonium chloride 

 solutions and have readily obtained the silky crystals. The 

 product resembles exactly the salt XH 4 PbI 3 .2H 2 0, except that 

 it is considerably paler in color than the latter. An analysis 

 of a pure product, carefully dried by pressing with paper, 

 showed that the formulae of both Poggiale and Yolkel are in- 

 correct, and that their products must have been contaminated 

 with ammonium chloride. The salt corresponds in type to our 

 double iodide. It loses one molecule of water on exposure to 

 the air for two or three days, becoming much darker in color ; 

 the second molecule of water goes off at 100°. 



Calculated for 

 Fgund. NH 4 Cl.PbI 2 .2H a O. 



Ammonium.- 3*33 3*27 



Lead 34-83-34-68 37*60 



Chlorine 5-11- 5-10 6'45 



Iodine 51-08-50-94 46*14 



Water 5'35 6*54 



The analysis indicates that the lead iodide and ammonium 

 chloride do not combine quite unchanged, and that the formula 

 XH 4 Pb(Cl,I) 3 .2H 2 possibly expresses the composition of the 

 product better than the one given above. In the course of our 

 experiments with ammonium chloride and lead iodide, we 

 obtained a crop of crystals which showed an almost complete 

 replacement of the iodine by chlorine. The salt was a 1 : 2 

 compound, a type which apparently does not exist among the 

 double iodides of lead. It gave the following analysis : 



Calculated for 

 Found. NH 4 Pb 2 Cl 5 



Ammonium 2-95 



Lead 66*82 67-93 



Chlorine 28*76 29*12 



Iodine 1-44 



The view that certain mixed lead double halides are to be 

 considered as variable mixtures of two isomorphous, unmixed 



♦Compt. Ttend., xx, 1180. f Pogg. Ann., Ixii, 252. 



Am. Jour. Scl— Third Series, Vol. XLYI, No. 271.— July, 1893. 

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