From E. A. Darwin [24 January 1825]1
I want you to try an experiment for me, & you remember you promised to do any I asked you & moreover to do them immediately. In a french book on physiology that I am reading it says that the affinity of saliva is so great for oxygen, that if gold leaf be triturated with it, it becomes oxidated. Now this I doubt, & I want you to try the fact wether it is so or no, & save you trouble I will write the experiment down
A. Triturate a small bit of gold leaf in pure water, & if that has no effect add a little gum.
B. Triturate it with saliva (give this a fair trial)
C If in either case it turns brown or yellow, in order to determine whether it is an oxide or simply in a state of fine division, the simplest way will I think be to digest it in Nitric Acid wh. will dissolve the oxide, & not the metal.
D. In order to be sure about the solubility of ox. of Gold in Nitric Ad., precipitate the N— Mur. of Gold with Lime water, & after washing the precip on a filter digest it in Nitric Ad.
Just try also whether the precip: after being heated red-hot in Spt Lamp in a glass tube for a few minutes is then soluble in Nitric Acid.—
I here send you a very correct picture of a curious stone I got out of the fire. There is another piece wh. exactly corresponds. In taking it out of the fire it dropped on the hearth, & divided so as to shew the impressions wh. I have represented, most probably vegetable remains. It appears to be quartz, & towards A is most beautifully coloured apparently with iron for towards B in the interi〈or〉 is a dingy red. Between A & B it is striated The 〈da〉rk blotch lower down appears to be carbona〈 〉 matter, & this together with the vegetable remain〈s〉 I thought never were found in quartz. It is not quartz I now see, but a kind of micaceous slate. The glistening deceived me.
Good Bye. yours truly. E. D.
P.S. If any body at home wants a copy of Bewicks Quadrupeds,2 there is a very decent copy at Deightons 2nd Hand for 17s. Demy 8vo.
P.S. 2nd. | I want you also to try if the per-oxide of iron is attracted by ye magnet, as also the sulphate.
I told you about the iron found in the tea by Price, I to-day tried the proportion & found it to be 13 per cent. Is not this an enormous imposition?
P.S. 3rd| I kept this open to wait for your letter which has just arrived, & for wh. many thanks.
It takes an additional night to go thro’ Cambridge.
I should conceive ye genera to be nil nisi fumus
There is no mineral seller here now
If you will send me the size of bottle I’ll get it, but if you go to London you can do it better at Newman’s.
Let me hear more about your school-plans. I should vote for your staying on till at least 18 years
Asks CD to do an experiment for him.
Has found a curious stone in his fire.
Price’s iron in tea measured 13 per cent.
Please cite as
Darwin Correspondence Project, “Letter no. 11,” accessed on 28 August 2016, http://www.darwinproject.ac.uk/DCP-LETT-11