192 H. L. Wells — Halides of Potassium and Lead. 



KI Pbl 2 I Volume. 





A 



450^ 



30§ 





15s 





? 





B 



425 





30 





50 





450 cc 









445 





40 





70 





470 





D 



445 





40 





100 





470 





E 



445 





40 





150 





460 





F 



200 





15 





15 





200 



gave the following results 



> on an 



lalysif 



s: 







K 





Pb 





I 





H 2 





A 



9-31 





22-03 





64-00 





4-69 



= 100-03 



B 



9-25 





22-30 











4-81 





C 



9-07 





22-03 





63-98 





4-89 



= 99-97 



D 



9-21 





21-98 





64-09 





4-71 



= 99-99 



£ 



9'20 





22-13 





64-17 











F 



9-27 





22-02 





63-84 











In these analyses and those which follow, water was deter- 

 mined by weighing it directly in a calcium chloride tube. The 

 other determinations were made according to the methods 

 mentioned in the preceding article on the double salts of lead 

 tetra-chloride. 



The above analyses correspond closely to the formula 

 K 9 Pb 4 I 19 .10H 2 O, but it will be shown beyond that the proba- 

 ble formula of the pure compound is K 9 Pb a l 8 .4H 4 0. This 

 requires K=7'25, Pb=25'56, 1 = 6274 and H Q = 4'45. If 

 this is the true composition, it must be assumed that all of the 

 analyzed products were contaminated with about 16'5 per cent 

 of potassium iodide, and that an excess of water was present, 

 possibly on account of the hygroscopic properties of that salt. 



It is to be noticed that the products were prepared under great 

 variations in the amount of iodine present, and it can be safely 

 assumed, from the care with which the products were examined, 

 that they were not contaminated with the salt KPbI 3 .2H a O nor 

 any similar compound. The amount of lead iodide in the solu- 

 tions was comparatively small, and a large part of it was used 

 in forming the salt under consideration, so that any contamina- 

 tion must have been chiefly potassium iodide. It is therefore 

 evident, since the salt is not decomposed on exposure, and 

 since the analyses show a constant amount of extra iodine in 

 spite of the variations of this ingredient in the solutions, that 

 the analyses must show the true ratio between the lead iodide 

 and the extra iodine in the pure compound. This ratio is 

 2PbI 2 :I in both K 9 PbJ 19 and K 8 PbJ 8 . 



The Bromide, K z Pb^Br % AJET^O : — This compound forms 

 dark brown, prismatic crystals which are solid and definitely 

 terminated, so that they do not have the tendency to hold in- 

 closed mother-liquor which the iodide has. The salt is easily 



