US2775504A

US2775504A - Method of removing hair and wool from animal hides and skins

Info

Publication number: US2775504A
Application number: US221115A
Authority: US
Inventors: Haskiel Zalcman
Original assignee: Individual
Current assignee: Individual
Priority date: 1949-10-18
Filing date: 1951-04-14
Publication date: 1956-12-25
Anticipated expiration: 1973-12-25
Also published as: GB706746A; BE510678A; FR1070436A

Description

METHOD QF-REMOVINGHAJR'AND WOOL FROM RIDES-AND SKINS Haskiel Zalcman; Braybrook, Victoria, Australia No-Drawing, ApplicationApi-il1%1951;

Serial=No.= 22-1,11'5.

Genus-priority; ncafibn-Ausannoctwer-rs; 1949 6. Claims. (Cl1.. 8=--94-.1-6)

This invention relates to the dehai'ring or removal. ofhair or wool frlom aniinal' skins. us'i'ngthe paintihgprocr ess wherein a paint composition is applied to the. flesh. side of theskinso that direct contact with thehair or wo'o'l is avoided'so far as is" practiable.

The inventionis also particularly though not. excliisively concerned with the removal of wool from sheepskins.

In the known or existing painting processes. for. d ehairing or de-wooliiig skins, it is. customary'toibrush. or spray theflesh side of the skin with a Paint? consisting of a .miXture of sodium sulphide (Nazsj-"and/or sodium: hydrosulp'hide (NaHS) and lime (CaO). in, water in the. desired"concentration with or withoutlaninert filler toproduce the required consistency.

The presence ofv sodium salts in such paints? results in. a relatively high pH value which causes appreciable. damage to the hide substance in the peltor. skinanc'Lto the Wool or hair. Moreover in addition to theactuah destruction of hide substance caused by the high pH.

value, the reaction between. sodium ions and. hid e asubstance in such paints at pH values? above .1010. .results.

in 'plumping or swelling of the pelt or skin which. is.

the cause offurther permanent damage. Plumping also... has an. adverse effect on depil'ation. because .it con'strictsx the, opening, of the hair. or woolv follicle. so. that. even. though the root is sufiiciently loosenedit cannot be readily pulledunless the bulk ofthe root is. pulped'by more. drastic chemicaliaction.

For a considerable ti'meithas been generally. recogk nized that whenever sodium sulphide nazs or..sodi-um\ hydrosulphide (N aHS) is used as a basic constituentiha pai'nt,'d'amage to the skins and; where the. is. a.

1 the range o'fabout 28% to about 4% each by weightof' sheepskin to the wool as Well is unavoidable. Wooliso. pulled is.not to be comparedwith-vi'rgin Wool,

fibers becoming h'arshand' reduced in tensile strength and.

elasticity. They are thickened so. that a woolofjfor in:

stance a 58 count is reduced in count toapprbximatelY.

56. The reduction in tensile strengthresults inalower tear intop-making and the wool is discolored. and. wil1l not dye evenly. As a result ofithisdamage thewooll' is invariably graded into a lower grade than virginiwool.

of the same fineness and character.

The. object ofthe present invention isto achieve.satis.-' factory depilation at av pH so far. below theefiective minimum in the prior art asto reduce damageinlhepelt.

orhair or wool to a negligible quantity. This is achieved: by 1 (a) Eliminating the cause, of. excessive. plumping,.and.. so avoiding the adverse binding effect on. the. hair: on

wool root.

(b) By increasing thehydrosulphiderion concentration and (c) By controlling the pliildown to the minimum value necessary for depilation having regard to the depilation load being kept to. at minimumrand thehydrosui'phiderion concentration being; increased: to can. economic: maximum;

These objectives are attained broadly by using a--paihfl= fen-example, .kao'lint.

.2. that: isrsubstantially devoid of' sources "of. monovalent' metal ions; and Which: isr maintained; ata pH of less than about L2. The: paint. contains: in addition: to water a source.- of. hydroxyl ions, a source of sulphideor hydrosulphide ions;. and: may contain-a buflfer substance for controlling or repressing the hydrox-yl' ion concentration of. the paint, thereby tocontinuously-maintain:thepaint at relatively. low pH? as compared with paints newcommonly used. a

Theseobjecti'ves are attained more specifically, and

' preferably, by'sel'ecting :as the unhairing accelerator calcium hydrosulphide (.Ca(HS )2.). which. by reason ofitspropertyof depressing pI-Iwhile. .not causing any Vplumpe ing beyond that. caused. byihn'e' alone enables the hydro sulphide ion concentrationltor be heavily increased;

The paint composition preferably comprises calciumhydrosulphide (-Ca'('HS)2) andfllime (CaO) and water mixed in l proportion, the concentration of-calcium-hydro' sulphide. .(.Ca( HS-) 2-) being within the range of about 2%.-to-about 30%: and the concentration? of lime ((CaO) being-.withimthe. range ofabout 33%: to 'about "l'% each by" weight-oft. the: compositioni to' forrn a .paint." of suitable concentration for. applicationvtoi the: skins; the consistency of the. fpainti being adjusted as necessary by the-addition: of. am inert' filler; The inert filler' may be;

The: inventioni relatesbasically to the method oidewooling; sheepskins -andrdehairing Iski'ns' whichhcomprise's applyingrto the flesh sideofirtheislins a paint cornposi tion compnisingca'lcium .hydrosulphid'e (Ca'(HS)2)' and lime- CaO.) and water'mixed rinsproportiong the; concen proved method iss'a composition conipris'iiig calcium hy-- drosulphide: (GatHSQa )E.-and:limei:(a0)' and water mixed in proportion the concentraisiontoti 'eal'cium' hydrosulphid'e (Ca(HS.).2) being within the range of a-bout.-3 to about" l0'%,.and. the concentration o' f' lime (cao being within the composition to form a paint of suitable concentration for application to the skins the consistency of the painti bein g adjusted as necessary by the a'dditi'on ofan inemefillerii I-t 'will be untle'rstood th'atthe ihventionalso provides the: method of-jde-woolin'g sheepskins and d'e-,

hai'riirg skin's; as hereinbefore describedbut using the last&

mentioned'composition.

The 'comp'ositionis prepared simply by mixing the cal ciumrhydrosulphide': '(Ca'( HS'-)2.)[ and jlii'ne'" (-CaO") and? waterriniproportiomwithbr withont the inert filler'as i's necessary forth'e' adjustment of the consistency of the" compositions, to obtain paints ofsuitable' concentration for application t'o the' 'sk-iiis; as explained hereinafter; r

The p'aintfis applied' to the skin by brushing or spraying-i omit) the fl'esli 'side of- 'the latter which is then-left for a predetermined period before the hair or wool is subjected to "the-pulling or other removing operation; Generally; the composition isof "such concentration; with relation to the nature of the skin as hereinafter more fully explained; that i't achieves its object in accordance with: the invention, within a b'out 24 hours after application toith'esk'ins.

rm th'er treatment i of skins other than 'sheepsli ins and hides, the period of depilation is lengthened a's-neeessary-- Patented Dec; 25 01 956 or hide to be treated.

In the prior art it was generally acceptedthat depilation was for practical purposes impossible at a pH lower than 12.3-12.5 which view led to the conviction that depilation by painting with a composition containing a high concentration of calcium hydrosulphide (Ca(HS)z) was quite impossible by reason of the progressive reduction in pH as shown by the following table based on the applicants work- EFFECT OF CALCIUM HYDROSULPHIDE (Ca(HS)2) ON THE pH OF CALCIUM HYDROXIDE (Ca.(OH)2) SUS- PENSIONS But it has been found by experiment by the applicant that efiective depilation of sheepskins can be achieved by painting with a concentration of calcium hydrosulphide (Ca(HS)2) as high as 30% by weight of the composition with the resultant pH as low as 9.9. At this concentration it was found to be unnecessary to provide more lime (CaO) than 1% by weight of the composition. For economic reasons such a high concentration of calcium hydrosulphide (Ca(HS)z) can be regarded as extreme and only significant as indicating the lower limits of hydroxyl ion concentration at which depilation is possible.

Further experiments demonstrated that with a concentration of calcium hydrosulphide (Ca(HS)z), as low as 2% by weight of the composition could be used if the proportion of lime (CaO) were increased to 33% by weight of the composition.

The results of the last mentioned experiment indicated that the pH (in this case 12.07) was higher than the optimum because the wool though much superior to wool removed by the sodium sulphide process was damaged to some extent.

Within these two extremes it has been found in practice that it is preferable to observe the following narrow limits according to the kind and type and condition of the skin and particular working conditions.

Calcium hydrosulphide (Ca(HS)z) about 3% to about Lime (CaO) about 28% to about 4%.

The experiments above referred to and the relative proportions of calcium hydrosulphide (Ca(HS)2) and lime (CaO) used bring out a number of factors, the significance of which appear not to have been appreciated in the prior art. Without a proper appreciation of them it was almost inevitable that it would be assumed, as was done, that satisfactory depilation with high concentrations of calcium hydrosulphide (Ca(HS)z), or equivalent sources of hydrosulphide ions, is impracticable.

The factors referred to are:

1. That the plumping or swelling of a skin resulting from the presence of substantial quantities of monovalent cations in the conventional sources of hydrosulphide anions, that is, sodium sulphide (NazS) and sodium hydrosulphide (NaHS), required a pH value high enough to pulp the bulk of the hair or woolroot, due to the fact that the follicle of the root was constricted by theplumping action;

2. Thatif a source of hydrosulphide anions associated with polyvalent cations is used a very much lower pH value would loosen the hair or wool root sufliciently to enable it to be removed since the plumping action isisubstantially eliminated;

3. That despite the facts that the depressing of the pH value of a lime suspension, as by the presence of calcium ions, is caused by the depressing of the solubility of the lime (CaO) or other source of hydroxyl ions, and that hydroxyl ions react by combination with collagen and saponification of fat in a skin thus involving a reduction of hydroxyl ion concentration available to react on the keratin of the hair or wool root, it is still possible I to bring sufficient additional lime (CaO) or other source of hydroxyl ions into solution to replenish the loss of hydroxyl ion concentration even where the pH of the composition when applied is as low as 9.9. This is to be explained by the following further factors;

4. That the loss of hydroxyl ions due to reaction with collagen and fat varies with the concentration of the hydroxyl ions at various pH values, and appears to be relatively insignificant at low pH values as compared with that at high pH values. This would appear to follow from the fact that the concentration of hydroxyl ions at a pH of 11 is only one-tenth of that at a pH of 12, and onetwentieth of that at a pH of 12.3;

5. That at any given solubility of lime the rate at which undissolved calcium hydroxide (Ca(OH)2) in a composition can be brought into solution, can be increased by increasing its bulk, and, therefore, the surface of it exposed to solution.

Having regard to the last two foregoing factors, it has been found that a proportion of 1% lime (CaO) provides a sufficient surface of undissolved or unhydrolized hydroxide (Ca(OH)2) to provide the necessary replenishment of hydroxyl ions at a pH of 9.9, and that at a pH of 12.15 a considerably larger proportion of lime (CaO) is required.

solution. Each of these factors must be taken into account according to the anticipated loss of hydroxyl ions. If the skin to be treated is a thick and/or fatty skin increasing the surface of undissolved calcium hydroxide (Ca(OH)2) exposed to solution may not be suflicient without reducing the proportion of calcium hydrosulphide (Ca(HS)2) so as to reduce the depressing effect of the calcium ion concentration on the rate of solubility. Experience has led the applicant to believe that it is desirable in some instances to limit the proportion of lime "(CaO) and therefore the surface of lime (CaO) exposed to solution to that which is no more than suflicient to overtake towards the end of the selected period of skin treatment, the loss of hydroxyl ions due to reaction. If the proportion of lime (CaO) is not so limited depilation will still be achieved but both the skin and the Wool will sufier some damage indicating that the hydroxyl ion concentration at its full strength reacts for too long a period on the skin and wool roots. Hence the desirability, if the best results are to be secured where adjustment of consistency of a paint is called for, for the addition of an PRACTICAL EXAMPLES OF TREATMENT Example 1 A sheepskin with a wool count of 58 after being washed, soaked and deburred was painted with a pain con- About 7% calcium hydrosulphide (Ca(HS)z) About 14% lime (CaO) About 6% kaolin About 73% water.

' After painting the skin was folded in the middle and hung over a wooden pole for a period of 24 hours. The wool was then removed from the skin. Upon inspection it was found that the wool had a quality superior to that obtainable by treating a similar skin according to the practices hitherto followed in the art, whilst the skin likewise was in a superior condition.

The skin treated in the above example was of average condition, i. e., characterized by that'degree of thickness and fat content associated with the skin of a sheep grown under average conditions as to rainfall in a locality suitable for the growing of wool of 58 count. The skin of a sheep grown under drought conditions, is less thick and carries less fat than the average and conversely a sheep grown under conditions of heavy rainfall and overabundant feed is thicker and carries more fat than the average.

Sheepskins vary as to thickness and fat content according to type as-well as condition and for a similar reason. Classified as to type according to the count of wool they carry skins carrying wool of higher counts are less thick and fatty than skins carrying wool of lower counts for the reason that fine wools are grown in drier areas than are coarse wools. But this variation is not very material in the case of skins carrying Wool of counts above 58 first because the variation is relatively slight and next because it is offset by the occurrence of folds in the skins of sheep carrying fine wools or what is described as a ribby condition in its skin. I

The composition used in the above example was found by trial to be that most suited to the treatment of skins of the type (expressed in terms of wool count) of a 56-58 count and of average condition. Taking this composition as a norm the operator should increase the proportion of calcium hydrosulphide (Ca(HS)2) and decrease that oflime (CaO) Where the skins have the characteristic of a lesser thickness and fat content than a skin of 56-58 wool count of average condition whether that characteristic is due to variation in type or condition or both. Conversely, where the skins to be treated are characterized by greater thickness and fat content the operator should decrease the proportion of- -calcium hydrosulphide and increase that of lime.

Example 2 As an illustration of adjustments which shouldbe made, the example of a sheepskin of average condition and havinga wool count of 50 may be quoted. A skin of this type and condition after being washed, soaked and deburred was painted with a paint containing About 3% calcium hydrosulphide (Ca(HS)2) About 25% lime (CaO) About71% water.

After. painting the skin was folded in the middle and hung over a wooden pole for a period of 24 hours. The wool was then removed from the skin. As in the case of the previous example it was found on inspection that both the 'wool and the skin were of superior quality and condition type' may beitreated in-the same manner-as skins of the type of a wool count of 56-58 with 'similarvari'ations according to condition.

With every skin of whatever type or condition it is necessary to apply a paint of lower calcium hydrosulphide (Ca(HS)2) concentration and higher lime (CaO) concentration to theneck and butt portions of the skin where the skin is thicker than it is elsewhere. As an indication of the adjustment here called for it may be taken that where a paint as in Example 1 above is suitable for the main part of the skin a paint as in Example 2 would be used on the neck and butt.

The proportions in all the above examples are adjusted to a period of depilation of about 24 hours at normal room temperature, say 70 or F. This period is normal practice in the fellmongering art'and the tfactthat it is so, operates very much to the disadvantage of'the users of paints hitherto used in the art. Operating at a high pH, as has been so in the past, it is impossible to I leave skins painted over a weekend without seriously increasing the damage to both skin and wool. This further damage is either accepted or the wool is pulled during the weekend at increased labor cost. By the practice of this invention skins may be left over a weekend before pulling without serious increase in damage to either the skin or wool.

The treatment of hides and skins other than sheepskins follows the same principles, but the period of depilation varies from 24 hours to 96 hours or even longer according to the thickness type and condition of the skin or hide to be treated.

A salted calfskin of approximate. weight 5 lbs. green Was washed and soaked for about 12 hours and then fleshed and painted with a paint containing,

About 5% calcium hydrosulphide (Ca(I-IS)2) About 7% lime (CaO) About 88% water.

After painting the skin Was folded in the middle and laid on a barrow for a period of 24 hours.

The skin was then dehaired in a skudding machine and it was found that the hair was in a good condition and the skin Was in good condition.

The best results are achieved particularly with sheepskins characterized by thickness and excessive fat by previous soaking and the action of machine deburring also contributes to more effective depilation at a minimum pH. Though soaking of the skin is not essential it is fotmd that after soaking the'proportion of (Ca(HS)2) may be increased and the pH of the composition consequentially decreased beyond what is necessary where there is no previous soaking.

Although calcium hydrosulphide and lime in the proportions indicated have been found highly satisfactory in practice, there are other substances and modifications of the process that may be used to obtain the desired results. The first requirement is that the paint bedevoid, or substantially devoid, of sources of monovalent metal ions, and this is true whether calcium hydrosulphide is used, or some equivalent substance. The substantial elimination of the sources of monovalent metal ions substantially avoids plumping or swelling of the skin, and thereby makes possible the use of lower pH solutions for the depilation of the wool or hair. This concept itself is of great importance in the practice of the invention.

Broadly speaking, the invention contemplates a composition substantially devoid of sources of monovalent metal ions, and comprising any suitable polyvalent metal source of hydroxyl ions, as hereinafter defined a suitable source of sulphide or hydrosulphide ions, and, where nec-' essary, a bufier material for controlling the hydroxyl ion concentration in the composition, so that the composition has a pH value of about 12 or less. Although lime is obviously the most practical source of hydroxyl ions, other suitable bases such for example as barium hydrox ide (Ba(OH)2) or strontium hydroxide (Sr(OH)2) might" 7 also beused, and possibly also magnesium hydroxide )2)- The hydrosulphide ion which must be present in suitable quantities to eifect depilation may be provided in various ways. The most effective source is calcium hydrosulphide which should be in the proportion of 2 to in order to maintain the pH of the solution below about 12.

Instead of mixing calcium hydrosulphide with lime, the hydrosulphide ions may be provided by passing hydrogen sulphide @S) into a slurry of lime in water, thereby forming a mixture of calcium hydrosulphide and unchanged lime. Or, the hydrogen sulphide could be passed into a slurry of lime and calcium sulphide, in which case the hydrogen sulphide would be absorbed and the pH of the solution lowered.

Instead of using a calcium salt as a base for the hydrosulphide ion, other metal sulphides may be used so long as the metal is not monovalent and the metal sulphide is appreciablysoluble in lime water, or, if not soluble, then if the hydroxide of that metal is even more insoluble in water, so that the metal sulphide will act with calcium hydroxide to form calcium sulphide or hydrosulphide and an insoluble metal hydroxide.

Accordingly, sulphides of barium, strontium, magnesium, and aluminum may be used satisfactorily, although in some instances of high solubility a buffer material would have to be used in order to control the pH to below about 12, such bufier being a suitable acid or soluble calcium salt.

Calcium chloride or a soluble calcium salt may be used as a control by providing calcium ions which repress the solubility of the calcium hydroxide to thereby maintain the desired pH value of about 12 or less.

Instead of using a soluble calcium salt a suitable acid may be used provided such acid produces a calcium salt that is at least moderately soluble. Thus, hydrochloric acid, acetic acid, hydrobromic acid, formic acid, lactic acid, nitric acid, nitrous acid, tartaric acid, and citric acid, are common acids whose calcium salts are soluble, and which wouldnormally provide the soluble calcium salt needed to repress the solubility of calcium hydroxide.

Even some sulphides that would normally be deemed ineffective in a lime solution, because they form insoluble sulphides, may be made effective if used with some added substance that would cause them to dissolve. All that appears to be necessary is that the-sources of monovalent cations are substantially avoided, that there be a suitable source of hydroxyl and hydrosulphide ions, and that the pH is properlycontrolled by butter substances when necessary to a value of about 12 or less.

In this specification and the following claims the word paint hasthe meaningunderstood by those skilled in the art of de-Wooling sheepskins and dehairing skins; the

lime .(CaO') found to achieve depilation within agiven period with the most favorable results as regards the skins and in the case of sheepskins the wool as well having regard'to the thickness and fat content of the skins; and, the expression inert filler means a finely divided substance the primary purpose of which'as an additive to the composition is to thicken the'consistency of the composition.

While I have described particular embodiments of my invention, it will occur to those skilled in the art that various changes, modifications and equivalents may be made or used without departing from my invention, and I, therefore, intend, in the appended claims, to cover all such changes, modifications and equivalents as fall within the true spirit and scope of my invention.

This application isa-continua-tiou in part of-my earlier application-Serial No. 180,897, filed August 22, 1950, now abandoned;

I claim:

1. In the art of depilating lamb and sheep skins by applying a depilatory paint to the flesh side of the skins, the method of effecting depilation to obtain high quality wool while preserving the quality of the skin which consists in applying to the flesh side of the skin an aqueous composition which is substantially free of sources of monovalent metal cations and which comprises calcium hydrosulphide and lime, the calcium hydrosulphide being about 3 to 7% and the lime about 25 to 14%, each by weight of the composition, the proportion of calcium hydrosulphide decreasing and of lime increasing within the above ranges with the increasing thickness and fat content of the skin, the composition having a pH of not more than 12 and not less than about 11.7, and the source of hydroxyl ions being suflicient in quantity to provide an undissolved reserve thereof suspended in the composition; allowing the composition to remain on the skin until the wool is loosened, and then pulling the loosened wool from the skin.

2. In the art of depilating lamb and sheep skins by applying a depilatory paint to the flesh side of the skins, the method of effecting depilation to obtain high quality wool While preserving the quality of the skin which consists in applying to the flesh side of the skin an aqueous composition which is substantially free of sources of monovalent metal cations and which comprises calcium hydrosulphide and lime, the calcium hydrosulphide being about 3 to 7% and the lime about 25 to 14%, each by weight of the composition, the calcium hydrosulphide decreasing toward 3% and the lime increasing toward 25% to provide a lower ratio of calcium hydrosulphide to lime when the composition is applied to the neck and butt portions of the skin as compared with the ratio of calcium hydrosulphideand lime in the composition applied to other portions of the skin, whereby the proportion of calcium hydrosulphide decreases and of lime increases with the increasing thickness and fat content of the skin, the composition having a pH of not more than 12 and not less thanabout 11.7,-and the-source of hydroxyl ions being sufficient in quantity to provide an undissolved reserve thereof suspended in the composition; and allowing the composition to remain on the skin until the wool is loosened.

3. In the art of depilating lamb and sheep skins by applying a depilatory paint to the flesh side of the skins, the method of effecting depilation to obtain high quality wool while preserving the quality of the skin which consists in applying to the flesh side of the skin an aqueous composition which is substantially free of sources of monovalent metal cations and which comprises calcium hydrosulphide and lime, the calcium hydrosulphide being about 3 to 10% and the lime about 28to 4%, each by weight of the composition, the proportion of calcium hydrosulphide decreasing and of lime increasing within the above ranges with the increasing thickness and fat content of the skin, composition having a pH of not more than 12 and not less than about 11.6, and the source of hydroxyl ions being sufiicient in quantity to provide an-undissolved reserve thereof suspended in the composition; allowing the composition to remain on the skin until the wool is loosened, and then pulling the loosened wool from' the skin.

4. In the art of depilating lamb and sheep skins by applying a depilatorypaint to the flesh side of'the'skins,

hydrosulphide and lime, the calcium hydrosulphide being about 3- to 10%andthe lime about28 to 4%, each'by weight of the-composition, the calcium hydrosulphide decreasing toward*3-% and the lime increasing'toward 28% to provide a lower-ratio of calcium hydrosulphide to'lim'e 9 when the composition is applied to the neck and butt portions of the skin as compared with the ratio of cal- 1 cium hydrosulphide and lime in the composition applied to other portions of the skin whereby the proportion of set forth in claim 1 in which the aqueous composition includes an inert filler in such quantity as to give the composition the consistency required for application and adherence to the flesh side of the skins.

6. In the art of depilating lamb and sheep skins by applying a depilatory paint to the flesh side of the skins, the method of effecting depilation to obtain high quality wool while preserving the quality of the skin which consists in applying to the flesh side of the skin an aqueous composition which is substantially free of sources of monovalent metal cations and which comprises calcium hydrosulphide and lime, the calciumhydrosulphide being about 3% to 30% and the lime about 33% to 4%, each by weight of the composition, with the lime being at least 7% when the calcium hydrosulphide concentration is at about 3%, the proportion of calcium hydrosulphide decreasing and of lime increasing within the above ranges with the increasing thickness and fat content of the skin, the composition having a pH of not more than 12 and not less than about 9.9, and the source of hydroxyl ions being suflicient in quantity to provide an undissolved reserve thereof suspended in the composition; allowing the composition to remain on the skin until the wool is loosened, and then pulling the loosened wool from the skin.

References Cited in the file of this patent UNITED STATES PATENTS Re. 4,549 Siebel Sept. 12, 1871 1,041,897 Stone Oct. 22, 1912 2,169,148 Jaeger Aug. 8, 1939 2,487,558 Kamlet Nov. 8, 1949 OTHER REFERENCES Thies et al.: article in J. A. L. C. A., vol. 37, 1942, pages 93-102.

Progress in Leather Science 19201945, pages 176, 118 and 189, pub. 1948 by Printing Craft Ltd., Mansfield, England.

Moore, in J. A. L. C. A., vol. 22, 1933, pages 206- 216.

Tanning Processes, by Orthmann, publ. 1945 by Hide and Lea. Publ. 00., pages 1, 2, and 41. (Copy P. O. S. L.)

Progress in Leather Science 1920-1945, page 188, publ. 1948 by Printing Craft, Mansfield.

Circular to Fellmongers No. 8, 3 p., September 1949, pub. by Commonwealth Scientific & Ind. Res. Or. Div. of Ind. Chem., Melbourne, Australia.

Bowes et 211.: B. L. M. R. A. Lab. Report No. 25, part V, 1946, 8 pages.

Claims

1. IN THE ART OF DEPILATING LAMB AND SHEEP SKINS BY APPLYING A DEPILATORY PAINT TO THE FLESH SIDE OF THE SKINS, THE METHOD OF EFFECTING DEPILATION TO OBTAIN HIGH QUALITY WOOL WHILE PRESERVING THE QUALITY OF THE SKIN WHICH CONSISTS IN APPLYING TO THE FLESH SIDE OF THE SKIN AN AQUEOUS COMPOSITION WHICH IS SUBSTANTIALLY FREE OF SOURCES OF MONOVALENT METAL CATIONS AND WHICH COMPRISES CALCIUM HYDROSULPHIDE AND LIME, THE CALCIUM HYDROSULPHIDE BEING ABOUT 3 TO 7% AND THE LIME ABOUT 25 TO 14%, EACH BY WEIGHT OF THE COMPOSITION, THE PROPORTION OF CALCIUM HYDROSULPHIDE DECREASING AND OF LIME INCREASING WITHIN THE ABOVE RANGES WITH THE INCREASING THICKNESS AND FAT CONTENT OF THE SKIN, THE COMPOSITION HAVING A PH OF NOT MORE THAN 12 AND NOT LESS THAN ABOUT 11.7, AND THE SOURCE OF HYDROXYL IONS BEING SUFFICIENT IN QUANTITY TO PROVIDE AN UNDISSOLVED RESERVE THEREOF SUSPENDED IN THE COMPOSITION; ALLOWING THE COMPOSITION TO REMAIN ON THE SKIN UNTIL THE WOOL IS LOOSENED, AND THEN PULLING THE LOOSENED WOOL FROM THE SKIN.