I am very sorry that I missed you the day before I set out on my journey. You will have learnt from your solicitor that I signed the articles. I still think I shall return before any powder will be made, at least if you do not make it till December, for our present intention is to be in town early in that month. I sent to you an imperfect copy of my book,[99] in which there were no engravings, and in which one cancel was not inserted, thinking that you would prefer a copy sent in that way: the cancelled leaf, which you have not, contains a correction for the quantity of nitrous acid gas and water to form the crystalline compound, which is the base of oil of vitriol. Three parts nitrous acid gas condense four parts sulphurous gas. I have my little apparatus, which will enable me to pursue my experiments on gunpowder. There is one conclusion very obvious resulting from the new facts,--a _perfect_ gunpowder ought to contain no more charcoal than is necessary to convert the oxygen of the nitre into carbonic acid. Sulphur forms from nitre just as much elastic fluid as charcoal, _i. e._ if similar quantities of nitre be entirely decomposed, one by charcoal, and one by sulphur, and if the sulphurous gas and the carbonic acid gas be compared, their volumes will be equal. The advantage of forming carbonic acid gas is, that it is more readily disengaged from the alkali. Now it is a question, whether sulphur will decompose _sulphate_ of potash,--it will decompose the carbonate; of this we are sure. There ought, then, to be just as much sulphur as will form sulphuret of potash with the potash: 191 of nitre, 28·5 of charcoal, and 30 of sulphur, are the true proportions for forming nothing but sulphuret of potash and elastic matter. Pray send me some cards to circulate; address to me, Post Office, Edinburgh. I hope you got Cavendish's balance. I have been here for two days:--it is a very magnificent place: good fishing for pike, trout, and grayling. Lady D. desires her kind remembrances. I am, my dear friend, Most affectionately yours, H. DAVY. [99] "Elements of Chemical Philosophy," to be presently noticed. TO THE SAME. Dunrobin Castle, near Golspie, August 21. MY DEAR FRIEND, I hope you are making progress in our manufactory. I shall expect, on my return, to find your powder the best and strongest, and to make trial of it. I wish I had some of it here, the black-cock and grouse would feel its efficacy. I have been expecting a letter from you every day. This house is so delightful, the scenery so grand, and the field-sports so perfect, that I think we shall not quit it for a fortnight.