Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/04—Mineral tanning
  • C14C3/06—Mineral tanning using chromium compounds

Definitions

• This invention relates totanning; and it comprises a method of converting hide into leather wherein a tanning bath is produced by the solution of an anhydrous chromium chlorid .in water, this chlorid being sometimes chromous chlorid but more frequently chromic chlorid in the presence of some chromous' chlorid or of a reducing body adapted to form chromous chlorid, such as ferrochrome, untanned hides being treated by such a bath; all as more fully hereinafterset forth and as claimed.
• Chromium has three states of oxidation, chromium trioxid,- ()rO (chromic acid); chromic oxid (sesquioxid) C50 and chromous oxid, CrO.
• the ratio of oxygen to chromium in the trioxid is twice as great as in chromic oxid; and that in chromous oxid is two-thirds that in chromic oxid.
• chrome iron stone it is usual to roast the ore in the presence of air'and alkali, thereby oxidizing the contained Cr O to form a chromate with the alkali present, this chromate being afterwards leached out. From the chromate other chromium compounds are prepared, if wanted.
• chrome tanning the active agent is Or o, which is taken up from slightly basic solutions by hide with the production of leather; the expression Cr Q, being used for convenience and without theory as to whether it is actually 013,0 or some hydrated form ofthe oxid in solution or colloidal suspension or forms a component of a basic salt. Not much is actually known as to this.
• Chrome tanning can be effected by the use of a.bichromate, usually sodium bichromate.
• the CF03 of the chromate is converted into C130, by reduction.
• glucose is sometimes added, together with sulfuric acid to combine with the base i of the .chromate.
• sodium bichromate In making chrometanning baths, sodium bichromate has the advantage of being a primary commercial material, other chromium comounds being usually made from it, and the urther advantage that it is a definite salt, not of a hygroscopic nature and is easily packaged, shipped and handled. But in the tan bath, it must undergo complex changes and the bath becomes loaded with inert products of reaction.
• a salt of chromium in the state of oxidation corresponding to chromic oxid invariably contains a salt of chromium in the state of oxidation corresponding to chromic oxid; this salt containing less of the negative radicle ((31,30 etc.) than corresponds to the normal salts, CrX
• a basic salt is present; this salt being usually considered CrX OH in which X denotes a negative radicle.
• dissolved chromic salts such as the sulfate and chlorid
• Cr,,() held in solution by the corresponding acid.
• tanning may be considered as a sort of competition between hide substance and acid for (lr o and the best tanning results are obtained from solutions in which the amount of acid is about two-thirds that theoretically required by the Or,(),; that is,
• chromates While the chromates have the advantage that they are relatively cheap, pure and easily obtainable, they present certain disadvantages in this relation.
• In use there is a necessary reduction of chromium trioxid to sesquioxid before tanning can be done; and an adjustment of base-and-acid relations.
• chromium chlorid is a more desirable body for making the tanning baths,'but unfortunately it has not been possible to obtain it readlly in a salt.
• Anhydrous chromic chlorid free from chromous chlorid, is a purple or violet crystalline mass which is insoluble in water and is readily stored, shipped and handled.v It is not in any way corrosive to metals and there is no difficulty in packaging it. In theserespects it has the advantage over any commercial hydrated form of chlorid. .In the presence of a little chromous chlorid,,anhydrous chromic chlorid becomes soluble in water; the proportion of chromous chlorid necessary to efi'ect this being extraordinarily little. In making chromic chlorid, it is practicable to turn out a product containing this small amount. Such a product while having all the other properties and advantages of the anhydrous purple chlorid just described, can
• Chromous chlorid is a yellow micaceous material soluble in water. Its solutions in water readily'oxidize to the chromic form and give a basic chromic chlorid containing two-thirds the chlorin necessary for normal chromic chlorid in other words, giving solutions at once adapted for tanning.
• these anhydrous chromium chlorids may be utilized in various ways in making standardized definite tanning baths without the necessity and nuisance of "the use of glucose and sulfuric acid.
• The'anhydrouspurple chromic chlorid in its insoluble form can be shipped and stored, as stated, without trouble and.
• Zinc can be readily brought into solution by the tanner by the use of a little reducing agent of any kind; something which will form chro- -mous chlorid.
• Zinc may be used.
• zinc as a reducing agent disposes of part of the chlorin and the solution formed is to that extent equivalent to an oxychlorid.
• the soluble form has practically the same advantages but requires no addition of reducing agent since it already contains some I (chromous chlorid).
• a very simple and efiicient way of making a tanning bath is to use a mixture of fine ground ferrochrome and anhydrous chromic in water. With -n'1ust be treated with alkali to obtain a basic chlorid. On treating this "mixture with hot itself is employed as a tanning bath.
• CrC-l quickly takes up oxygen and is converted into the equivalent of Cr Ol O, or 'a soluble basic chlorid.
• the preparations in question have the advantage of offering the tanner something which can be made of definite composition as regards chromium content and which is very rich in chromium.
• the Cr O equivalent of chromic chlorid is about the same as that of sodium bichromate, while that of chromous chlorid or of a mixture of chromic chlorid and ferrochrome is considerably higher.
• anhydrous chromous chlorid in the desired amount may be dissolved in hot water and the bath directly used.
• Basic chromic chlorid is formed as rapidly as hide will take up C130 Additions of soda are made from time to time after the first tanning action is complete.
• the anhydrous chromic chlorid may be aced in hot water with a little zinc or a ittle finely ground ferrochrome and the solution directly used as a tanning bath.
• Tanning may be done in the usual ways, by drumming, etc. In drumming the agita tion of the bath provides aeration. v
• What I claim is 1.
• tanning hides and skin the process which comprises exposing untanned hide to the action of a solution containing chromic and chromous chlorids.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)

Priority Applications (3)

Applications Claiming Priority (3)

Publications (1)

Family

ID=60201726

Family Applications (1)

Country Status (3)

Families Citing this family (1)

• 1925
  • 1925-08-13 US US50137A patent/US1723568A/en not_active Expired - Lifetime
• 1926
  • 1926-08-03 FR FR619777D patent/FR619777A/fr not_active Expired
  • 1926-08-12 GB GB19912/26A patent/GB256979A/en not_active Expired

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