PART III. CHROME LEATHER 



SECTION I. THE NATURE OF CHROME 

 LEATHERS 



IN these days the manufacture of chrome leather has 

 attained a position hardly less in importance than that 

 occupied by the ancient method of tanning by means of 

 the vegetable tanning materials, and large quantities of 

 hides and skins are now " chrome- tanned " after pre- 

 paratory processes analogous to those described in con- 

 nection with vegetable tannages (Part II., Section II. ; 

 and Part II., Section I.). 



Chrome leathers are made by tanning pelts with the 

 salts of chromium, and are typical of what are known as 

 " mineral tannages," in which inorganic salts are the 

 tanning agents. Tannage with alum and salt (see Part 

 IV., Section I.) is one of the earliest mineral tannages, but 

 is now of relatively minor importance. Chrome tanning 

 was first investigated by Knapp (1858), who experimented 

 with chromic chloride made " basic " by adding alkali, 

 but his conclusions were unfavourable to the process. A 

 patent was taken out later by Cavallin in which skins were 

 to be tanned by treating with potassium dichromate and 

 then with ferrous sulphate which reduced the former to 

 chromic salts, being itself converted into ferric salt. The 

 product, which was a combination of iron-chrome tannage, 

 did not yield a satisfactory commercial leather. Another 

 patent, taken out in 1879 by Heinzerling, specified the use 

 of potassium dichromate and alum. This in effect was 

 a combination chrome- alumina tannage. The alum had 

 its own tanning action and the dichromate was reduced 



