TALBOT3824

44 Queen Ann S^{t 1}

Feb. 28^th

Dear Sir

As there appeared to be some little difference of opinion between us the other day respecting the iodide of silver, I enclose specimens ² of my manufacture. According to me there are 3 different things confounded together hitherto under that name; the first, ³ is very sensitive to light & is what you make use of in your experiments.

The second, ⁴ a pale yellow iodide, is insensible to light: but on the other hand, sensitive to heat. If you try this specimen before a hot fire, (an almost scorching heat is required) you will see it turn to a full & bright yellow, & then back again as soon as it is cold.

The third, ⁵ or white iodide, is insensible both to light, & heat. The specimen I send is not a good one since there is a patch of the yellow kind on it, which is sensitive to heat.

Believe me
Yours very truly

H. F. Talbot