SOURCE OF THE CARBON AND NITROGEN OF PLANTS. Produce of Carbon in Forests and Meadows supplied only with mineral aliments prove it to be from the atmosphere. Relations between Mineral constituents, and Carbon and Nitrogen. Effects of the Carbonic Acid and Ammonia of Manures. Necessity of inorganic constituents to the formation of aliments, of blood, and therefore of nutrition. NECESSITY OF INQUIRIES by ANALYSIS to advance AGRICULTURE. LETTER XVI RESULTS OF THE AUTHOR'S LATEST INQUIRIES. Superlative importance of the PHOSPHATES OF LIME and ALKALIES to the cultivation of the CEREALIA. Sources of a SUPPLY of these MATERIALS. LETTERS ON CHEMISTRY LETTER I My dear Sir, The influence which the science of chemistry exercises upon human industry, agriculture, and commerce; upon physiology, medicine, and other sciences, is now so interesting a topic of conversation everywhere, that it may be no unacceptable present to you if I trace in a few familiar letters some of the relations it bears to these various sciences, and exhibit for you its actual effect upon the present social condition of mankind. In speaking of the present state of chemistry, its rise and progress, I shall need no apology if, as a preliminary step, I call your attention to the implements which the chemist employs--the means which are indispensable to his labours and to his success. These consist, generally, of materials furnished to us by nature, endowed with many most remarkable properties fitting them for our purposes; if one of them is a production of art, yet its adaptation to the use of mankind,--the qualities which render it available to us,--must be referred to the same source as those derived immediately from nature. Cork, Platinum, Glass, and Caoutchouc, are the substances to which I allude, and which minister so essentially to modern chemical investigations. Without them, indeed, we might have made some progress, but it would have been slow; we might have accomplished much, but it would have been far less than has been done with their aid. Some persons, by the employment of expensive substances, might have successfully pursued the science; but incalculably fewer minds would have been engaged in its advancement. These materials have only been duly appreciated and fully adopted within a very recent period. In the time of Lavoisier, the rich alone could make chemical researches; the necessary apparatus could only be procured at a very great expense.