24 Wells—Compounds containing Lead and extra Lodine. 
Johnson’s analysis differs chiefly from the new ones in its 
higher iodine and consequently lower oxygen as determined by 
difference. His oxygen is considerably too low for the amount 
required to give CH,CO, with the carbon and hydrogen, and 
this was evidently the main cause of his inability to arrive at 
a rational formula. It seems probable that there was an error 
in his determination of iodine. 
Gréger’s salt.—A compound has been described by Max 
Gréger* as corresponding to the remarkable formula, PbO. 
PbI,.I,. As he prepared it, it was an amorphous precipitate 
which had been washed with water, and exposed to the air for 
a long time in order to allow iodine with which it was mixed 
to evaporate, and, consequently, there seemed to be room for 
doubt as to its freedom from decomposition after it bad under- 
gone these operations, even if it could be supposed to have 
been a pure substance when it was precipitated. 
I have undertaken a reinvestigation of this salt, and have 
succeeded in preparing it in a beautifully crystalline condition 
in which there was no doubt abont its purity, and have found 
that Groger really analyzed a pure compound, but that he over- 
looked some water that it contained. With the addition of 
one molecule of water his formula becomes correct, but this 
formula, Pb,I,O.H,O, or as it may be written Pb,I,(OH),, is 
no less remarkable than the one which Gréger advanced. 
This substance, in a crystallized condition, had been observed 
in this laboratory a short time before Gréger’s work was 
known here. At my suggestion, Mr. J. H. Pratt had made 
some experiments with the dark colored precipitate produced 
by mixing strong aqueous solutions of lead acetate and potas- 
slum triiodide. Such precipitates were collected upon filters, 
treated while still moist with boiling alcohol and the resulting 
liquid, after filtration, was evaporated over sulphuric acid, with 
the result that small, brilliant, black crystals were sometimes 
‘obtained. Several partial analyses of this substance showed 
that it contained lead and iodine in the ratio 2:5, and were as 
follows: 
Ratio of | Calculated for 
i. II. LU: average. Pb.I;0.H20 
heads 2) S7.a4. ere 37°32 2°00 . 38°23 
Todine .._ 57°66 58°71 58°62 5°07 58°63 
The yield of this product was very small, and it was difi- 
cult to obtain it in a pure condition since it was often mixed 
with the well-known compound PbIOH and with other sub- 
stances which were not identified. The presence of water in 
the salt was established, but the cireumstances were such that 
the investigation was interrupted at a point where the pure 
* Monatshefte fiir Chemie, xiii, 510, 1892. 
