SECTION IV. FORMALDEHYDE TANNAGE 



THE use of formalin for hardening gelatin has long been 

 known, but it was left for Payne and Pullman to devise a 

 commercial process for tanning pelt into leather by means 

 of formaldehyde (H.CHO) solutions. Their process, which 

 was patented, specified the use of alkalies in conjunction 

 with formaldehyde or other aldehydes. The function of 

 the alkalies is not very obvious, for it has been shown that 

 formaldehyde will tan also in neutral and in acid solution. 

 The precise action of the aldehydes is also as yet somewhat 

 obscure, but it is noteworthy that very small proportions 

 of formalin will give a complete tannage. It is probable 

 that the action of formaldehyde is not perfectly analogous 

 with that of its homologues, for it is a most reactive substance, 

 and will certainly with proteids undergo reactions which 

 are not analogous to those with other aldehydes. The 

 leather obtained by tanning with formalin is quite white 

 and resembles buff leather, but has advantages over the 

 latter in that no bleaching is necessary. 



According to the patent specifications the pelt should be 

 drummed in water and the tanning liquor a solution of 

 formalin and sodium carbonate added gradually at 15- 

 minute intervals. Up to 6 hours for light skins, and up to 

 48 hours for heavy hides, are required for complete tannage. 

 The temperature is raised during the process from 100 to 

 118 F. The tanning liquor may be made from 16 Ibs. of 

 commercial formalin (36 per cent, formaldehyde) and 32 Ibs. 

 soda (80 per cent. Na 2 CO 3 ) in 10-15 gallons of water. This 

 should be added, one gallon at a time, to 4 cwt. pelt in 100- 

 120 gallons of water. After tannage is complete the goods 

 should be paddled with a i J per cent, solution of ammonium 

 sulphate to remove the soda, and " nourished " in a solution 



