378 M. C. Lea—Laboratory Notes. 
chromate was added. A red precipitate that did not redissolve 
was produced. 
7. To a similar strong solution of sodic citrate, citric acid 
was added, and the experiment repeated under these condi- 
tions. The first drop of chromic solution did not produce a 
precipitate ; a little more produced a precipitate not redissolving 
"8. To a strong solution of sodic citrate with silver, as in (6), 
oxalic acid was added. The first drop troubled the liquid; a 
little more produced a heavy precipitate. 
In the first four of these trials, silver solution was added to 
one of sodic citrate, containing the oxalic, tartaric, &c., acids. 
In the three in paragraph (5), the solution of sodic citrate was 
charged with as much silver as it would take up, and this was 
added by degrees to the solution of chromate, oxalic acid, &c. ; 
in (6), (7) and (8), this was reversed and the precipitating solu- 
tion was added by degrees to a very large excess of the solution 
of silver in sodic citrate. Thus the trial was varied in every 
possible way and in every case precipitates were obtained, often 
with extremely small and always with small quantities of the 
precipitant. 
IL. Molecular conditions of certain Lodides. 
If mercuric iodide be dissolved in a quantity of boiling 
water and the solution be poured out, one-half into a cold por- 
celain basin and the other into a beaker of cold water, the 
iodide quickly separates in both cases, but in the former wit 
a bright scarlet color, in the latter with a pale yellow, and only 
after some hours’ standing recovers its normal scar. 
When nickel iodide (obtained by dissolving nickel carbonate 
in aqueous hydriodic acid) is evaporated in a basin, an the 
sides of the basin above the liquid become hotter than 212°, 
the adhering nickel iodide turns black. Paper dipped in the 
solution and heated turns intensely black. Nickel chloride 
shows the same result, but at a ete, temperature. Potassi¢ 
bromide dissolved with the nickel chloride lowers the tempera 
ture at which the blackness comes. j 
is blackening is permanent and the paper itself is acted 
upon. The change takes place far below the temperature at 
which paper chars. 
Ill. Criticisms on some results of M. S. Bottone. 
In the December number of this Journal appears an abstract 
of some experiments of M. S. Bottone, directed to prove that 
the hardness of any element is as the specific gravity divid 
by the atomic weight. The hardness of each element, caleu- 
