My dear M^r. Darwin

I am quite ashamed of myself for not having answered your letters,¹ but the fact is that they followed me about Europe for several weeks before I received them, & then I had no books to refer to.

The phosphate of ammonia which you obtained from Messrs Hopkin & Williams would be, I imagine, the Diammonic Phosphate the sp. gr. of which is 1^.678.²

The nitrogenous substances produced during the putrefaction of animal matters have been little if at all investigated & I am unaware of any material which occupies such a relation as urea to the original substance. The decay of flesh skin &c. in contact with air & water is attended with the rapid production of nitrate & carbonate of ammonia.³

I fear this information comes too late to be of any use. I have just returned to England after an absence of 3 months.

Yours very sincerely | E. Frankland