Wells—Compounds containing Lead and extra Iodine. 25 
material at hand had been exhausted and no accurate determi- 
nation of water had been made. 
My thanks are due to Mr. Pratt for his valuable assistance 
in the investigation of the compound up to this point. When 
I subsequently obtained Gréger’s salt in a crystallized condi- 
tion it proved to have the same form and composition as the 
product mentioned above, so that a further study of the latter 
was deemed unnecessary. 7 
In order to obtain Gréger’s compound in a well crystallized 
condition, it is necessary to modify his method of preparation 
by using a small amount of acetic acid. It is also advanta- 
geous to use boiling water instead of cold water for the precipi- 
tation, and to use a somewhat larger volume of this than is 
recommended by him. [ have obtained the best results by the 
following method: Dissolve 10 g. iodine in 100° absolute alco- 
hol, then 50 g. crystallized lead acetate in 150° water, 3° glacial 
acetic acid and 300° absolute alcohol. Mix the two solutions, 
let stand 14 to 16 hours at the temperature of the room, filter 
to remove the small precipitate, then dilute with 1500° of boil- 
ing water. Let the wholestand until cold, when the compound 
sought will have erystallized out mixed with iodine. Pour off 
the liquid and wash the crystals with cold alcohol in small 
- quantities until the iodine is removed. Dry the product upon 
filter-paper, and then in the air at ordinary temperature. 
The product consists of very brilliant black crystals, usually 
0°5™™ or less in diameter. They form octahedrons, apparently 
of the tetragonal system, with faces that are much curved 
and otherwise distorted. The powder of the crystals is similar 
in color to Gréger’s precipitate, and it agrees with it in being 
practically stable in the air and scarcely acted upon by cold 
water or alcohol. 
Two separate crops of apparently perfect purity were ana- 
lyzed. Lead and iodine were determined by the methods 
described above under Johnson’s compound. Water was col- 
lected and weighed in a calcium chloride tube, the substance 
being ignited in a tube behind a layer of granulated sodium 
carbonate which held back the iodine completely. Free iodine 
was determined volumetrically by the use of sodium thiosul- 
phate solution. The results were as follows: 
Found. Calculated for 
il. PboI,(OH)s. 
jie (0 Ca 38°54 wore. 38°23 
Todime asa 2. 58°41 58°62 58°63 
Waterers Sa 1°83 1°82 1°66 
Oxygen (diff.) _... 1°42 1°34 1°48 
100°00 100°00 100°00 
“Hree” jodmerm.. 34°78 ees: I 35°18 
Loss by heating .. 36-43 36-43 I,+H,O 36-84 
