After the leather has been thoroughly tanned and rinsed, or scrubbed by a brush-machine or broom, it will tend very much to improve its color and pliability to stack it up in piles, and allow it to sweat until it becomes a little slippery from a kind of mucus that collects upon its surface. A little oil added at this stage of the process, or just before rolling, is found to be very useful. Great caution is necessary in the admission of air, in drying when first hung up to dry. No more air than is sufficient to keep the sides from moulding, should be allowed. Too much air, or in other words, if dried too rapidly, in a current of air, will injure the color, giving a darker hue and rendering the leather harsh and brittle. * * * * The average time of tanning in 1842, was five months and seventeen days; of 1843, five months and twenty-two days; 1844, six months; 1845, six months and eleven days; average of the whole time, five months and twenty-seven days. The average weight of the leather was over eighteen and one-half pounds per side. This, according to the best authorities we have, is considerably below the time employed in England. There, it is no uncommon thing for eight or ten months to be employed in tanning a stock of leather, and some of the heaviest leather, it is said, takes fourteen and eighteen months. Such deliberation undoubtedly insures a fine quality of leather, but it may be questioned whether there is not a great loss of weight—a loss of interest on capital, and in consequence an unnecessary enhancement of price, which does not suit the American market. The tanning of leather, more than almost any other manufacture, is a chemical process, the success of which depends almost wholly upon the skill and judgment with which its complicated manipulations are conducted. To attain the requisite skill in the laboratory of the chemist, is evidently impossible; it can only be acquired in tanning itself, by long and careful attention and observation. The labor in the loft and peeling bark during the above five years was 8820 days. One man will work through the beam-house, in one year, 6260 sides. One man will tan and finish 2228 sides. One cord of bark tans 196 pounds. The question has been frequently asked me, how long does it take to tan sole leather. I answer, from four to six months, according to the strength of the liquor and the number of sides in the vats; and the quicker tanned the better. If the hides are fresh, they are capable of being properly softened, and, if so, the process of tanning may be completed much sooner than in the case of old and hard hides, that cannot be softened with the same facility. If the hides have sufficient room in the vats, so as not to lay crowded, they will tan much faster. As the tanning advances, the liquor should be renewed seasonably, and its strength increased in a ratio proportionate to each stage of tanning.