212 Mr. Warington on the Biniodide of Mercury. 
his claim No. 5 is incorrect. With respect to the claim No. 7, 
my observations regarding the effects of polarized light apply 
to the last set of experiments on the precipitated iodide while 
suspended in the mixed solutions, and therefore Mr. Talbot’s 
remarks, referring as they do to the sublimed crystals, cannot 
in the slightest degree interfere with them. As to the quoted 
expression, “ the field of view appears scattered with the most 
brilliant assemblages of (rubies, topazes, emeralds and other) 
highly coloured gems,” &c., the names of which, inclosed in 
the parenthesis, have, inadvertently I presume, been omitted 
in the quotation, the only similar word that I can find which 
occurs in my own description of these appearances is the word 
‘ gems,’ and if the use of that expression, applied as it is to 
the precipitated biniodide of mercury, is to be considered as 
implying a piracy on Mr. Talbot’s application of it in viewing 
the crystals of sulphate of copper by polarized light, I can 
only plead the poverty of the English language, as I had never 
seen Mr. Talbot’s paper (Phil. Mag. vol. v. p. 324) until he 
publicly drew my attention to it. 
In the concluding paragraph of Mr. Talbot’s letter he first 
states that “the second part of my paper, however, contains 
a fact both new and important,” and then immediately after- 
wards proves that it is not new at all, for that he described in 
1836 a phenomenon of the same kind previously unexampled, 
and that this is only a second example. Now surely these 
statements are perfectly contradictory. Observed facts can- 
not be new and old. But let us examine in what respects 
these phzenomena are alike. Mr. Talbot takes iodide of 
lead, prepared through the medium of the acetate of that 
metal and iodide of potassium, while fresh, he does not say 
whether it was washed to remove the acetate of potash or not, 
and warms it over a spirit-lamp, when certain beautiful changes 
are observed. My own observations are on the precipitated 
biniodide of mercury, which is known to be first precipitated 
yellow, then gradually to deepen in tint, and ultimately to be- 
come scarlet ; under the microscope the first precipitate 1s in mi- 
nute crystals of the rhombic form, similar to the yellow sublimed 
salt, and these slowly and spontaneously become disintegrated, 
dissolve and are replaced by the octohedron with the square 
base like those obtained by the more cautious sublimation. I 
am at a loss to imagine where the similarity between them ex- 
ists. It would take up too much space to go further into this 
matter, and I must content myself with leaving it to the study 
of any of your readers who may wish further to analyse this 
subject. Again apologizing for thus occupying so much room 
in your Journal, I remain, Gentlemen, Yours, &c., 
Apothecaries’ Hall, 0 
Wet.) 1248. Rospert WARRINGTON. 
