82 farmers' and mechanics' journal. 



for many months ; but on a small scale, the whole tan may be re- 

 moved from an ooze in a few hours. For this purpose, the astrin- 

 gent matter beiug ground to powder, 1000 grains are to be infused 

 in water at about 100*, and after the whole of the tan seems dis- 

 solved, the fluid must be strained, and the insoluble matter, wash- 

 ed, till the water passes through tasteless. A certain quantity of 

 this, say one-tenth, is to be placed in a bottle, along with some 

 pieces of skin, previously washed with warm water, to dissolve the 

 lime, employed in taking oif the hair, and to remove the loose gela- 

 tin ; the skin being dried by exposure to air, and weighed before 

 being put into the bottle. Leaving them there for a few hours, 

 turning them frequently, the whole of the tari will unite with the 

 gelatin, and thus convert the skin into leather, so that, by drying 

 it, and weighing, we find the quantity of tan that existed in the in- 

 fusion, of course of 100 grains of the astringent matter. 



The best skins for this purpose, are the fresh curriers' shavings 

 from the strong hides, intended for harness, or ox-hides split very 

 thin. They must, after being treated as above mentioned, and 

 weighed, be put into tepid water, and handled for a few minutes, 

 to open the pores, and allow them to imbibe the tan." 



There are a great variety of vegetables, which abound in tan- 

 nin ; probably many, which have never been used for the purpose 

 of tanning skins. An artificial tannin has been made by Mr. 

 Hatchett, " by the action of heated diluted nitric acid on charcoal, 

 and evaporation of the mixture to dryness. From 100 grains of 

 charcoal, Mr. Hatchett obtained 120 grains of artificial tannin 

 which like natural tannin, possessed the property of rendering skin 

 insoluble in water. 



" Both natural and artificial tannin form compounds with the 

 alkalies and the alkaline earths ; and these compounds are not de- 

 composable by skin. The attempts that have been made to ren- 

 der oak bark more efficient as a tanning material by infusion in 

 lime-water, are consequently founded on erroneous principles. 

 Lime forms with tannin, a compound not • luble in water." 



The quantity of tannin varies, in the same substance or bark, 

 according to the time of vear in which it is cut, and also according 

 to the temperature in different seasons. " When the spring has 

 teen cold," says Davy, " the quantity is smallest. On an a crage, 

 4 or 5 lbs. of good oak bark are required to form 1 lb. of leather. 

 The inner cortical layers in all barks, contain the largest quantity 

 of tannin. Barks contain the greatest proportion of tannin at the 

 time the buds begin to open — the smallest quantity in winter." 



Some very good remarks upon tanning different kinds of leather, 

 have appeared in the Technical Repository/, which we shall copy in 



