The analyses show a striking resemblance to those of the soda deposits of Wyoming, given by Dr. Attfield,[17] except that their percentage of sodium carbonate is smaller, which is quite intelligible in the light of Mr. Brunner’s abstract on the ‘Probable origin of natural deposits of sodium carbonate,’[18] which supports the view that the sodium carbonate is derived from sodium sulphate by the reducing and carbonating action of low organisms. [17] Journ. Soc. Ch. Ind., 1895, p. 4. [18] Ibid., 1893, p. 116. It may be noted here that the preservative properties of sodium sulphate are well known, and the anhydrous sulphate has been recommended as a substitute for common salt (see p. 23). Drying is a very common method of preserving hides as well as other putrescible matters. It has no effect in killing bacteria, but putrefaction can only go on in presence of a considerable amount of moisture. As applied to hides, it is, to the tanner, one of the least satisfactory modes of cure, involving very considerable difficulties in bringing hides back to the moist and swollen condition which is necessary at the outset of his operations, but it is the only practical method in districts far from the coast and with primitive modes of transit, both on account of the cost of salt, and the lessened weight of the dried hide. Great differences are found in the ease with which dried hides soften, according to the way in which the drying has been accomplished, the difficulty being greater the higher the temperature which has been used (see p. 111). The best mode of drying is to hang in the shade in a good draught of cool air, with the flesh side out. Hides or skins dried in a tropical sun are not only difficult to soften, but are liable to damaged portions, which either refuse to soften, or blister and go to pieces in liming, owing to the structure of the hide being destroyed by heat, the outer surface drying first and forming an impervious layer which hinders evaporation from the inside, so that the moist interior becomes melted, while the outside appears quite sound. Such injuries are often only to be discovered by soaking and liming. Very similar damage may occur from putrefaction of the interior after the outside has become dry, and to get good results, the drying must be gradual, but rapid, especially in hot climates. South American hides are mostly dried in the sun, suspended by head and tail from stakes, with the hair side out.