TANNING MATERIALS AND TANNERIES 165 



IV. Quickness in filling orders and amount of investment required. 



V. Cheapness of manufacture. The best leather is produced slowly only by use of materials rather 

 poor in tannin. 



(G) STATISTICAL NOTES: — 



I. One ton (2,240 pounds) of hemlock bark will tan 300 pounds of sole leather or 400 pounds of 

 upper leather; 4 to 5 pounds of good oak bark are required to produce 1 pound of sole leather. 



One acre of hemlock forest is said to yield about 7 cords of bark, and 1,500 board feet of timber 

 are said to carry, on an average, 1 cord of bark. 



One acre of hardwood forest will yield, on an average, not to exceed one-half cord of chestnut oak bark. 

 The form height for chestnut oak bark ranges between 0"10 and 0'18. 



II. One hundred pounds of dry hides yield 150 to 185 pounds of leather; 100 pounds of green hides 

 yield 60 to 80 pounds of leather. The cost of the hide amounts to from 50 to 75 per cent of the cost 

 of production. 



III. The number of tanneries in (he United States has greatly decreased from the year 1880 (5,628 plants) 

 to the year 1910 (597 plants). The small tanneries using old fashioned and wasteful methods have been 

 outclassed by the large and intelligently conducted modern plants. The leather trust controls over 100 of 

 the largest plants. The tendency of the tanneries is a gradual shifting towards the waterfront. 



IV. "Hides" are obtained from oxen, cows, and horses; "kips" from yearling cattle; "skins" from 

 calves, sheep, goats, and pigs. 



Calf skin is used for upper leathers of shoes; sheep skin for cheap shoes, linings and gloves; goat 

 skin for fine upper leathers and gloves. 



Hides are often split, and the so-called grain and flesh splits are used in place of goat and calf skins. 

 The best and strongest leather is obtained from the back of the animal close to the spine. 



(H) MANUFACTURE. The old fashioned methods used from time immemorial consisted of rinsing 

 the skins; scraping-off the flesh; treating the hair with lime; placing alternating layers of crushed oak bark 

 and of skins in rough vats. The time consumed in this process of manufacture frequently exceeded a year. 

 The best leather, however, is produced in this way. 



The modern process in manufacturing sole, belt, and harness leather is: — 



I. Soak in soft water (heated to less than 70 degrees F.) to remove salt and blood and to restore 

 the original softness and pliability of the skin. Remove blood, dirt, flesh, and fat from inner side of hide. 



II. Loosen hair either by liming green hides in milk of lime for three to six days or by sweating dry 

 hides at 70 degrees in a closed room, inviting a partial decomposition of the hair sheath. The sweating 

 is preferred for acid hemlock tannage. 



III. Remove on the "beam," by hand or machine, the hair and the lime. 



IV. Prepare the liquors in the leech house. Cold water extracts only part of the tannin from either 

 bark or wood. Very hot water may extract all, extracting with it, however, undesirable coloring matters 

 and killing the fermenting microbes. Aside from the mechanical imbedding of molecules by impregnation, 

 a chemical action (fermentation) is supposed to take place in the case of bark tannage, due to the presence 

 of microbes in the bark, chemically binding the tannin to the albumen and gelatine of the skin. 



V. The tannage itself is either "acid hemlock tannage," or "non-acid hemlock, oak, and union tannage." 

 (a) Acid hemlock tannage consists of:- 



1. Coloring in a dilute solution of tannin. 



2. Placing skin for 2 to 4 days in a sulphuric or lactic bath (of 10 to 30 per cent) by which the 

 hide is swelled to a great thickness. 



3. Placing the hide in a strong, concentrated solution of tannin. 



