SECTION II. BYE-PRODUCTS OF THE 

 GELATINE AND GLUE TRADES 



FROM the skin gelatine and glue trades the most valuable 

 bye-product is the grease, which is obtained from the 

 " fleshings " of the adipose tissue. These fleshings are 

 themselves a bye-product of the leather trades. The 

 recovery and purification of this grease has been dealt with 

 previously (Part V., Section II., p. 227). In the skin glue 

 trade the only other bye-product is the residue from the 

 extraction process (Part V., Section III., p. 230). This 

 residue is known usually as glue " scutch," and is composed 

 of the proteins of the skin which are insoluble in hot water. 

 These insoluble portions are obtained from all layers of the 

 skin. There is much hair often in scutch, the hyaline or 

 glassy layer (grain), and the elastic fibres of the corium are 

 also insoluble, and a proportion is derived from the fibres 

 of the adipose tissue on the flesh side. All these portions 

 are fairly rich in nitrogen, and the scutch has, therefore, 

 considerable value to makers of fertilizers. It is liable to 

 contain also a percentage of grease, which is usually removed 

 by steaming under hydraulic pressure. This process recovers 

 a valuable bye-product and increases the manurial value of 

 the scutch. There is always left in scutch some of the 

 gelatinous skin substance which, strictly speaking, should 

 have been removed during extraction. There is, however, 

 a practical limit beyond which it does not pay to do this. 

 When this limit is reached the cost of steam in extracting, 

 and also in evaporating and drying, together with the loss 

 of time and labour involved by occupation of the plant, is 

 greater than the value of the possible product. 



From the bone-glue industry, the grease is similarly a 



