THE LEATHER INDUSTRY. 
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Cuemistry or Vecerantre Tannine Process Stint Oxscurr. 
Vegetable tanning, as its name implies, consists in the conversion 
of hide into leather by means of material procured from plant life. 
The barks of trees, such as the hemlock and oak, the wood of quebracho, 
chestnut, &c., and the leaves and fruits of many plants contain matter 
which is soluble in water and capable of tanning hides. The hides 
upon coming from the beam-house are first suspended in vats containing 
very dilute solutions of these tanning materials, each day or two they 
are moved into stronger liquors, and are finally hauled out when the 
colour of the tan liquor has completely penetrated the hides as shown 
by examining a cutting in the thickest part of a hide. 3 
Simple though this process may seem, its chemistry is exceedingly 
complex. Many theories of the mechanism of the process have been 
propounded, and there is still no general agreement on any theory. The 
process is one in which the tanner finds he dare not deviate much from 
his daily practice. If the liquors become too strong or too acid, there 
is danger of the grain surface becoming rough or wrinkled to such an 
extent that it cannot later be made smooth and the value of the leather 
_is lessened considerably. If the liquors are not sufficiently acid, the 
tanning action is retarded and the liquors and leather become darker 
in colour through oxidation. aie 
Different kinds of tanning materials often ‘produce very different 
kinds of leather, but it is still a matter of some doubt as to whether such 
differences are due to differences in the active tanning principles which 
they contain or to differences in the content of foreign matter, such 
as acids and sugars or other fermentable substances. | Some evidence 
has been brought forth recently to show that astringent tanning ma- 
terials differ from milder ones chiefly in possessing less of non-tanning 
matters of acid character. Many difficulties that sometimes confront 
the tanner in the later processes are traceable to slight changes in the 
condition of the tanyards. 
VecerasLe Tannina Proprems Surrep ror Untversrry ResEarcu. 
Much of the research required on the subject of vegetable tanning 
is especially suited for university laboratories. Among the more im- 
portant problems in this connexion might be mentioned the chemistry 
of the tannins, the swelling of the collagen fibres by dilute acid solu- 
tions and the opposing action of the tannins, the diffusion of the con- 
stituents of a tan liquor into the substance of the hide fibres, the effect 
of change of acidity upon the tanning action, and the nature of the 
tanning action itself. It will be found convenient in university studies 
of these problems to use a standard hide powder which has been placed 
on the market by the Standard Manufacturing Co. of Ridgway, Pa., 
especially for use in tannin analysis. This powder is made up chiefly 
of purified collagen fibres containing about 12 per cént. water, 0.3 per 
cent. ash, and about 0.8 per cent. of fat. : 
Curome Tanninc. — 
Chrome tanning consists in treating the hides first with a solution 
of sulphuric acid and common salt, a process known as pickling, and 
then with a solution of basic ‘chromic sulphate corresponding roughly to 
(MENG Egan 
