SCIENCE AND INDUSTRY. 
The Utilization of Leather Waste.” 
BY A. HARVEY. 
The profitable utilization of scrap leather is a problem which has 
often occupied the minds of tanners, and has been the subject of a 
large number of patent specifications in this country and abroad. In 
the majority of cases such specifications deal with the manufacture of 
leather substitutes or “recovered” leather from such scrap, but it 
must be remembered that there are other outlets which can be, and 
are, sometimes considered, viz. :— 
1. Detanning and preparation of glue. 
2. Manufacture of leather boards. 
3. Manufacture of fertilizers. 
DrranNING AND GLUE-MAKING. 
One of the best known of the earlier patents on this subject is by 
Trotman, in which the finely divided leather is soaked in dilute acids 
or lime water, and then treated with sodium peroxide or some other 
oxidizing agent capable of liberating hydrogen peroxide. In the case of 
chrome leather, such treatment converts the chromic oxide into alkali 
chromate, which can be recovered, while the residual skin or hide: 
substance can be treated in the usual manner for glue manufacture. 
Stripal in English Patent 3437/1910 detans chrome leather by 
heating the material, previously cut in small pieces, with a } per cent. 
solution of either hydrochloric or sulphuric acid to a temperature of 
50-100° C., whereby it is claimed the leather is detanned almost 
immediately. An ingenious idea is embodied in an American patent 
by Holloran. . The leather is put into a vat containing a solution of 
common salt, through which an electric current is passed, after which 
it is washed in a bath of chlorine water, and again in clean water. 
This effects detannization, and from the hide is prepared a glue 
by the ordinary processes. As a by-product, sodium hypochlorite 
ean be made by mixing the electrolyzed solution with chlorine liquor, 
when precipitation of the tannin matter also takes place. Another 
process for chrome-tanned waste is by Sadlon. Here the leather is 
soaked in caustic soda solution until it becomes pulpy. The mass is 
afterwards neutralized with acid and washed with water, when it can 
be converted into glue by merely gently warming, and not boiling, as 
is usually the custom, with water. 
The most modern process for dealing with chrome leather is that 
worked out by Lamb, and is given in English Patent 182,864/1920, In 
this case use is made of organic acids containing two or more hydroxyl 
groups, such as lactic, tartaric, malonic, and oxalic acid. ‘The leather 
waste is soaked in this acid solution until detannization is complete. 
From the liquor is recovered the chromium and the detanned material 
used for the making of glue. The present writer has seen some good 
elue stock made by this method. 
* Extract. from The Leather World. 
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