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Native Patagonian Salt.—I see that the salt procured from the "Salinas" or salt lakes and plains of the interior of South America, is spoken of by Mr. Darwin as being objected to on account of its extreme purity, which appears to me a very strange objection to a chemical substance, although I recollect hearing some time ago, in a discussion about copper sheathing for ships, that copper of a certain degree of impurity was more durable as sheathing than that which approached nearer to the standard of absolute purity. The two cases, however, I imagine to be widely different. The salt from the "Salinas" is brought to market and used just in the state in which it is collected from the borders of those lakes, whose retiring waters leave, in the dry season, a saline incrustation upon the soil. When this has attained a sufficient thickness—say two or three inches, it is broken up with hand-spikes and crowbars, and carried to market either by mules to the mines or in ox-carts to Buenos Ayres. It undergoes no purification either by solution and crystallisation, or by any other method; but whether it be for the use of the Saladeros on the coast, for the amalgamation of silver ores in the districts of the mines, or as a condiment to the food of the inhabitants, it is consumed in its crude unprepared state, and of course from the mode of its deposition and collection, is necessarily greatly mixed with earthy impurities, although this varies much with the seasons. Indeed, the fault of excessive purity seems a very strange one to find with an article used in its natural and unprepared state, and one which neither its appearance nor its taste would have led me to suspect. I never heard the miners find any fault with it at all except as to comparative value as to the quantity of earth in it. The country people will sometimes apologise for the strange colour of the compound when called upon to set some before an Englishman; and the conductors of Saladeros (or establishments for the manufacture of oxen into cured hides, jerked beef, &c.), who were obliged to use a good deal of it during the blockade of the river by the Brazilians, object to its use from a far different cause. The cakes or pieces into which the salt crust is broken up, present no distinct crystals; but appear as an amorphous mass, which when broken down for use become almost a soft powder, and when applied to the meat dissolves with great rapidity, so that a much larger quantity is consumed in curing the beef, than when the rough, strongly crystallised salt of the Cape de Verd Islands is made use of. The beef is made much salter, which deteriorates its quality, and every atom of salt used is gone almost as soon as it is thrown on the beef; whereas, when Cape de Verd salt has been used, and the beef has lain in a good heap, and been turned and drained, and is sufficiently impregnated with salt, a large quantity may still be shaken from the surface of their slices as they are taken from the heap to hang upon the frames to dry; and as this spare salt is in rough sharp crystals, it is just as good as fresh salt for using another time; and from this mechanical difference principally the salt of the Salinas is, no doubt, 50 per cent. less valuable than that of the Cape de Verd to the conductor of a Buenos Ayrean Saladero. In fact, it is contrary to reason and experience, to suppose that any native salt found in amorphous masses, or in a finely divided state, intermingled with earthy matter, can be more pure than a kind which presents a hard, large, and clearly defined crystal. Still I believe that for a native product, the Patagonian salt is remarkably pure.—W. B. N.