THE TECHNOLOGIST. [Oct. 1, 1864. 



104 ON CHEMISTRY APPLIED TO THE ARTS. 



the fluid through the skins into the vessels below. Mr. Turnbull's pro- 

 cess, being an imitation of that used for tanning morocco leather, need 

 not be described. Attempts have been made from time to time to mine- 

 ralize, that is to say, to substitute for tanning, mineral salts, as will be 

 described in my next lecture, when speaking of the art of tanning skins. 

 The processes which have attracted most notice in this branch of the art 

 of preparing leather are those of Messrs. D'Arcet and Ashton, M. Bordier, 

 and M. Cavalier. M. Bordier's plan is that of dipping hides in a solution 

 of sesqui-sulphate of iron, when the animal matters of the hide 

 gradually combine with a basic sesqui-sulphate of iron, rendering the 

 hide imputrescible, and converting it into leather. M. Cavalier's method 

 is to dip hides first into a solution ol proto-sidphate of iron, and then 

 into one containing alum and bichromate of potash. A chemical action 

 ensues by which the proto-sulphate of iron is converted into a persul- 

 phate, combining with the animal matter, and by its preservative action, 

 together with that of some of the alum, the hide is converted into 

 leather. I think, however, that I shall bz able to satisfy you, from the 

 results of many examinations of leather and hides which I have made, 

 that there are good and sufficient reasons why most of these processes 

 have necessarily failed. Inventors have been led to believe, by the state- 

 ments of many eminent physiologists (as can be proved by reading some of 

 the most recent works on that science), that skin is composed of blood- 

 vessels, glands, &c, plus gelatine, and that if by any mechanical con- 

 trivance the tanning liquor could be brought into contact Avith this 

 gelatine, the leather would be tanned ; and many ingenious schemes 

 have been devised, and much money expended, to obtain that result. 

 The fact, however, is that there is no gelatine in skin, for if there were, 

 when hides were placed in water, the gelatine would be dissolved and 

 washed away. But what is supposed to be gelatine in the hides is in 

 reality the isomeric substance called osseine, or one greatly resembling 

 it. The great discovery to be made in the art of tanniug, therefore, is 

 that of a chemical or fermentative process, by which the isomeric change 

 (that of the osseine into gelatine) may be rapidly produced, instead of 

 by the slow putrefactive process which occurs in the old method of 

 tanning. Further, I would observe, that to convert a hide into leather 

 it is not sufficient that the whole of its animal matter be combined with 

 tannin, for the leather thus obtained would present two great defects : 

 1st, the hide would not have increased in weight, and the tanner's profits 

 therefore would suffer ; 2ndly, the leather would be so porous as to be 

 useless for many of the pnrposes for which leather is required. The 

 reason of this is, that when, after a period of several months, the osseine 

 has been converter] into gelatine, and this has become thoroughly com- 

 bined with tannin, a second series of reactions is necessary to render the 

 leather more solid and less permeable to water, ancl to increase mate- 

 rially its weight. These reactions constitute what is called feeding the 

 hide, and are brought about by leaving it to steep in more concentrated 



