In a former Letter I expressed a doubt, whether the Barilla of Spain, were the Same Plant as the Soda or Kali: but have Since found that it is.

In the Dictionaire Æconomique, under the Word Barille, I find it described as The herb from the Ashes of which are extracted the best Salt of Alicante, which for that reason they call "Salt of Barilla.[”] "(Soude de Barille)," and which is precious for the manufactures of glass and Soap. The Salt of Barilla, is considered as the best for the fabrick of the finest Mirrors.

I have translated the French word "Soude" by the English word "Salt," though in the French it Seems to be an appropriate technical term, to Signify the Salts extracted from vegetables chiefly marine, by combustion. Yet the French Writers are not Steady in the Use of it. They Sometimes apply it to the Plant "Soda," but most commonly and correctly to the Salt of Soda. The English have no other word than "Salt" that I know to express the Sense of "Soude."

In Dr Michells communication to our Academy, a great deal was Said about "Soda" as the most power full antiseptic in Nature. Whether he was acquainted with the natural history of the Kali or Soda I know not. In Sir John Pringles Works, which unfortunately I have not, you may probably find much information on this subject.

All Vegetables are Said to contain more or less of these Salts, which may be extracted from their Ashes, Mustard, Cresses, Onions, Cabbages, Celeri, Sage, Wormwood especially: flowers of Camomile, roots of Gentian, green tea, root of Valerian, Jesuits Bark &c. But do We know how they operate on the human Body, any better than We know how manures operate on Land?

Nature keeps her Secrets with great Care, especially from your Friend