Bourne Archive: Muspratt: Hide Preparation               Latest edit 27 Dec 2010


The Bourne Archive


Muspratt’s Chemistry, Theoretical, Practical & Analytical (ca. 1859)

Extracts Concerning Leather, 6: Preparation of the Hides.

The web pages linked from this introduction are from an article on tanning, under the heading ‘Leather’. The original article is presented here in several web pages, respectively dealing: 1, with leather; 2, with tanning materials; 3, Sources of tannin; 4, crushing mills; 5, varieties of skin; 6, hide preparation; 7, the common tanning process; 8, finishing processes; 9, fancy and speciality leathers.

Vol. 2. pp. 511-516

Preparation of the Hides.—The tanner, previous to submitting the hides, skins, of kips, to the true tanning process, is under the necessity of subjecting them to one or more preliminary operations, with the view of removing dirt, particles of flesh, and in most cases the hair and epidermis; and the manner in which these are effected is of great importance, as much of the success of the subsequent process, and, consequently, of the quality of the leather, depends upon it

Cleansing.—The hides which have been recently taken from the carcass of the animal require but very little labor to purify them from any filth which may remain attached to them, unless, indeed, as is said to be sometimes the case, they are wantonly saturated with such matters in order that they may weigh heavier. Sometimes, however, such green or fresh hides, as they are called, when they cannot be immediately disposed of to the tanner, or when the latter does not intend to submit them at once to the processes by which they may be made into leather, are salted to prevent putrefaction 1. When the hide has to remain for a period of a week, four or five pounds of coarse salt are used to preserve it; if a month, double this quantity is deemed requisite. Foreign hides—such as those from South America—receive more than the above quantity; in some instances as much as twenty pounds of salt per hide are used, according to their size and season, but the average for foreign hides is about fifteen. All these matters must be separated by steeping and washing; and hence one of the absolute requirements of a tannery is a profusion of water. Green hides are steeped in water during a period of one to twelve hours, according to the quantity of blood and dirt they hold, at the end of which time they must be thoroughly rinsed before removal. In many cases much greater pains must be taken, such as repeated scrapings of the hide with a blunt tool on the beam or support, trampings 2 in the water buckings 3, et cetera. If a current of water is available, much labor is spared by fastening the hides to a rack fixed to the face of the stream, for the friction of the water will detach the impurities without the aid of much mechanical labor. When dried hides, or such as are salted and dried, are treated, the difficulties are much greater, since a longer period of time is required to soften and bring them into the condition of fresh ones. With these soakings, trampings with the feet, handlings
that is, the removal from the water or steep—and scrapings are multiplied before they attain the softness and purity of clean fresh ones. In large establishments the mechanical labor required is executed by a kind of mill, similar to that for fulling cloth, wherein the hides are exposed to the continued action of two heavy stocks 4, which squeeze out the slimy matter and dirt that might induce a putrefactive fermentation. The immersion and handling even in this case require to be alternated with the action of the machine; and it is necessary to remark that where vats or tanks are used, the water should be frequently renewed, otherwise, if the contents happen to get stale or overcharged with the slimy extract from the hides, and the time of submersion be prolonged, there is danger of putrefaction, and, therefore, of injury to the skins. Where only water is employed for the above purpose, it is necessary to keep in view the quality of this liquid, irrespective of the change which it undergoes by saturation with the nitrogenous matters, dirt, et cetera, from the hides. When very calcareous, its cleansing qualities are less effective than when the water is soft; but, independently of this, it is believed that hard water affects the hides in another way, by which their softness and porosity are injured owning to the fatty and other matters which may be in an incipient state of decomposition, forming combinations with the earthy bases which fix themselves to the skin 5.

In many parts of France and Belgium, they employ a weak solution of lime to assist in cleansing and freshening the hides, with the view, at the same time, of rendering the succeeding operations of depilation and tanning more easy and efficacious.

Depilation.—After the thorough softening and cleansing of the hides, they are next submitted to a further immersion in baths or tanks with compounds which effect the solution of the cellular matter in which the hair is rooted, or are otherwise exposed to the action of agents which operate towards the same end. A variety of methods are practised by tanners for the solution or softening of the matter which binds the epidermis and hair to the true cutis, or that portion of the skin that enters into the formation of leather, with the view to their removal. The most important of these are the lime process, the sweating or fermentative process, the rhusma and gas lime process; and latterly, in America, the cold sweating mode has been introduced with success.

By Liming 6.—Of these processes the liming is by far the oldest, and is still very extensively adopted, but with greater caution than in former times. In its action it is not so quick as certain other agents, necessitates much future labor, and frequently is the cause of injury to the leather; still, probably from its cheapness and the effect of custom, it is more resorted to than any other. Generally speaking, it is now used in the form of a semi-liquid or milk, formed by agitating a certain quantity of it with a given body of water—about eight bushels to one hundred and fifty gallons. The liming is carried on in a series of pits or tanks, sunk in the floor of the liming house; these are built of bricks or masonry, and well cemented, and have an outlet at the bottom for the purpose of drawing off the fluid contents when necessary. Their dimensions vary according to the requirements of the establishment, and the number of skins to be operated upon at once. In some parts of France and Belgium, well bound wooden tubs are preferred. The number of these varies from five to twelve, and the solution in them is so arranged, that there is a regular increasing graduation of density from the first to the last, even where the larger number is taken advantage of. The first of these, called usually the dead vat, contains very little caustic lime, and this is the one to which the hides after washing are exposed, in commencing the operation. Here they remain for one, two, or three days, according to circumstances, and during this period they receive a handling at regular intervals, some twice, and others three times a-day. This handling merely consists in taking the skins out of the pit or tub, and laying them on a plank or inclined board near the tank, and introducing them again. Before the re-introduction, the contents of the tank are well agitated, with a view to distribute any undissolved quick-lime throughout the liquid, so that there is no partial or undue effect experienced on the skins. The workmen likewise contrive to spread out the latter in the vat as much as possible, and so every part has the same exposure to the lime. In the dead vat, however, there is left very little if any quick-lime undissolved. After spending the allotted time in the first vat, they are transferred to the second, which contains a stronger liquid, or more lime, and left in this, with occasional overhauling, for a few days, after which they are put into the third, and so on till the hides ultimately arrive at the last vat, which contains the fresh lime. In operating in this rotation the dead vat of one batch of hides becomes the live one of the next, and so on in succession. The time which the skins take for thorough liming, varies according to their weight and texture. Thus the lighter skins, as of the sheep, are sufficiently acted upon in three to five days, but ox hides, kips, and calf skins, require two to three weeks, according to the season. Formerly the process of depilation extended over a period of three to fifteen months, and even eighteen, the hides being steeped in the weak lime vats a considerable part of this time, but such procedure is now entirely relinquished. In many parts of the Continent, however, the operations preparatory and conducive to the depilation last two and three months; but in these cases the skins are partly swelled, so that, for this special treatment, they do not require so much attention in the succeeding stages. The quantity of lime which is used by the different tanners is somewhat various, and dependent upon the size of the hides, but the average is from eighteen to twenty-four gallons of Fig. 347. The Beamfreshly-burned fat lime—three to four cubic feet measure—for a hundred hides of average size. The lime is permitted to slack in the strong or live vat, and afterwards stirred about with a wooden spatula, to distribute it equally in the liquid.

Fig. 348. The Scraping KnifeWhen the epidermis is sufficiently softened it is detached, together with the hair on the beam. This is an arched wooden or stone bench—Fig. 347—upon which the hide is laid, with the flesh side inwards, and the hair removed by the scraping knife, shown in Fig. 348. After the separation of the hair and epidermis, the loose fragments of skin are pared off, as likewise the flesh and fatty matters adhering to the reverse side—such fleshings being economized in the preparation of glue 7. The implement used for the latter purpose is a long, straight knife, having a sharp edge. This is called the fleshing knife, and is Fig. 349. The Fleshing Kniferepresented in Fig. 349. After the last operation, it is necessary to submit the hides to thorough rinsing in the stream or vats, in order to remove all uncleanness, lime, et cetera, as much as possible. It often happens that the hides present inequalities as to thickness and the like, and to reduce them to average homogeneity, they are treated with the smoothing or polishing stone, represented in Fig. 350. Fig. 350. The Smoothing Stone.This tool is of sandstone, interiorly moulded, so as to lie parallel upon the beam, fixed to a piece of wood, and furnished with handles, with which the hide is rubbed, to bring the part to an equal thickness as nearly as possible. This operation is not so much practised by English as by continental tanners. By repeated scrapings in this way with the knives and stone, alternated with steepings and washings, the dirt, hair, fleshy parts, and lime are removed as effectually as possible, previous to the true tanning operation. In the large English tanneries the scraping and fleshing of the hides are executed by mechanical contrivances, and so the manual labour is greatly diminished. Machines for this and other purposes have been constructed by several, among others by Poole, Plant, and Woodworth.

Bating 8.—With respect to the removal of lime from the skin, it has been found that no amount of scraping and rinsing is capable of making a perfect separation, a portion of the earth being retained in the pores of the skin, combined with, perhaps, some of the decomposing tissue, and with the grease and fat of the hide, as a lime soap. These combinations, if not altered and removed, obstruct the union of the tannic acid with the gelatinous fibre of the skin, and not only this, but they communicate a rigidity to the leather which excludes it from such applications as require a soft, tough, and pliable material. Several plans are employed to remedy this defect. The old method is that which is known as bate, or grainer, that is, a menstruum prepared by macerating the excrements of pigeons, pen-fowls, and of dogs, in water, and immersing the scraped and clean skins in it for a certain period, when, it is stated, the lime is separated by a chemical decomposition that takes place and renders it soluble. The proportions employed are from ten to twelve gallons of fresh dung to one hundred, or less if they are large skins; and the time of steeping stretches over ten days in ordinary weather, but less time is required if the liquid be warmer. In this treatment, likewise, the repeated handling and scraping on the beam are resorted to. Investigation has shown that the above matters contain an ammoniacal chloride that parts with its chlorine on coming into contact with the lime, and so gives rise to a soluble combination of this base—chloride of calcium—that may be readily abstracted by water. That this disgusting method should still continue to be so extensively practised is disgraceful to modern science. It is stated, that in London alone not less than five thousand pounds are annually expended in collecting and purchasing the above materials, for the sole use of the tanners of the capital and its suburbs.

Although this method of bating the hides is tolerably effective, yet it is well known to be attended with serious disadvantages, not the least of which is the putrefaction of the bate that is going on during the steeping, and which injures the hides by acting upon the tissue of the skin, reducing its weight in the first instance, and in the second, rendering it incapable of yielding the quality of leather it would doubtless produce, did the above change not occur. Taking the hint from the action of the alkaline chloride in this case, some tanners have attempted to prevent the putrefaction induced by the bating with excrements by avoiding its use altogether, using hydrochloric acid in a diluted state as a substitute. The innovation has not yet become very general in England, although many tanners, especially in Paris, are reported to have practised it successfully, the object of the expulsion of the lime being satisfactorily gained by it, and in addition to this, the swelling of the hides also. Sulphuric acid has likewise been proposed as a substitute of the bat, but the effect of this is not so powerful as that of the acid already mentioned, since it constitutes with the lime a very insoluble compound. The acid is, however, almost always resorted to for raising or swelling the skins, preparatory to submitting them to the tan-pits. MacBride in 1774 was the first who showed that it possessed this property. Turnbull introduced the use of saccharine liquids 9 for removing the last portions of lime from the hides, as well as for softening the hair and cuticle. Four or five pounds of coarse sugar or treacle dissolved in sixty to seventy gallons of water, constitute the bath. The sugar in this process forms a soluble saccharate of lime 10, which is removed by soaking and rinsings. A new process, in connection with others, for the purpose of facilitating tanning and improving the leather, was patented in 1841 by Warington. It consists in employing carbonate of ammonia instead of the usual bate for the graining of the skins; but although this salt converts the lime into a neutral compound, it does not remove it, and consequently, the flexibility and softness of the leather must suffer.

Depilation 11 by Acids.—Besides these methods, by which the influence of the lime on the skin is counteracted, others are employed which dispense with it in the first instance. Acid liquors have long been known to operate upon the roots of the hair and epidermis, so as to detach them from the skin. The Calmuck-Tartars employed a bath of sour-milk for this purpose, and in Paris the same agent is adopted at the present time. Another menstruum, obtained by the fermentation of barley or rye meal, was once very extensively used as a steep for hides for separating the hair. Here, together with the fermentation, the active body was acetic acid resulting from the latter. This, in common with other acids, such as sulphuric, hydrochloric, oxalic, et cetera, operate so as to soften the epidermis and hair, to an extent sufficient to enable the scraping process to cleanse the skin from them. Tanners urge, however, that by their use the skins are swelled to such an undue extent as almost to render it impossible to prepare good compact leather from them. The weak vegetal acids, however, are not excluded from practice, more especially in France, Belgium, and parts of Germany. Many of the Paris tanners submit the hides, after they have been soaked in water, washed, and fleshed, to a number of acid vats, in a way analogous to the liming. Generally, the series of baths consists of five, which from the first to the last increase in power and efficacy; the first is usually intended to cleanse the hides, the second to soften the hair and epidermis for the depilation, and the other three to swell and give body to the skins. This operation, which is called the white dressing, requires a period of five weeks in the summer and six in the winter season. The quantity of farinaceous matter which is taken varies at different establishments; in some cases one hundred and forty-five pounds of barley-meal, and in others, one hundred and fifty or sixty are employed. The dressing is generally made by leavening one-tenth of one-fifteenth for the bulk till it becomes sufficiently sour; It is then softened with hot water, and after the whole has become a thick homogenous fluid, free from lumps, it is added to the remaining quantity of the meal in the vat, and tepid water in sufficient quantity poured in to fill the vessel. In some cases yeast is added to quicken the fermentation. Eight or nine hides are worked in each vat, and as in the lime process, the weak or first vat passes in succession from one to the other in rotation. The final vat is composed with sixty pounds of meal leavened and thinned with water, and left to develope acetic acid for fifteen days. In all of these operations the handling and working the hides on the beam at regular intervals are indispensable.

By Sweating.—The depilation is effected at the present day by many English and continental tanners, more especially the latter, by what is known as the sweating process. Various means are adopted, but the principle common to all is the softening or the epidermis, by fermentation, or putrefaction. In Paris and other parts of France, one-half the hide is sprinkled with some chloride of sodium and the other half lapped over it, with the view of arresting the effect of the putrefaction which succeeds from injuring the tissue of the skin. Several hides are then piled one upon another in a pit or other convenient place, and left till the incipient odor of ammonia is observed. This is a sign that putrefaction has commenced, and therefore, that the hides are approaching a state in which they readily part with the hair. As the fermentation thus excited would be very deleterious to the leather-making portion of the hide, too great caution cannot be exercised in order to arrest the action as soon as the hair is softened. With this view, the hides should be examined once or twice a day, refolded and piled again, till it is discovered that the hair will readily yield. The same result is attained, without the precaution of adding salt, in Germany and some parts of Great Britain, by simply piling the hides upon one another in a pit. The moisture and circulation of the air acting upon the nitrogenous matters—blood, sweat, and other impurities—readily augment the heat of the whole mass; and incipient putrefaction, recognizable by the evolution of ammonia, follows. It is necessary to examine the hides frequently, lest the action should prove injurious. In many instances they are piled between layers of stable dung in a heap, and the whole covered with the same material, till the hair becomes detached, care being taken, however, to examine the hides every twenty-four hours or less.

Steam and heated vapors have also been tried as agents for removing the hair from the skin. M. Dellut was the first to suggest the use of steam, and his method was carried into effect in several French tanneries. The hides are suspended in an airtight chamber of suitable dimensions, and which is furnished with a perforated, false, or second flooring. Steam is introduced beneath the perforated flooring, and ascends among the hides, through the small orifices, so as to keep the interior of the chamber at 68° to 80°,12 but not beyond this; for, in the event of the temperature becoming elevated, the gelatinous matter of the skins would more or less enter into solution with the condensed steam on them, and consequently, would afford a less weighty leather. When due attention has been paid to the operation, the hair and epidermis becomes sufficiently softened in twenty-four hours to be removed with the hairing knife. Compared with the putrefactive sweating process, this method is a decided improvement, as the liability to injury is very much diminished.

Bg 13 Cold Sweating.—In America, especially in New York, New Hampshire, and in many parts of the Northern division of Pennsylvania, a process is in general use, called the cold sweating, by which the hair can be removed, and a yield of leather estimated at seventy to eighty per cent. acquired; whilst, by other means employed, such as by steam and lime depilation, not more than thirty to forty per cent. of the dry hides are retained as leather. Besides this very material gain, and other advantage follows, namely, that the laborious cleansing and fulling required in the other modes, is unnecessary; and consequently, the hides retain their natural density, a condition which very much improves the quality of the leather. The operations by which this is effected, are thus stated in a foreign journal:—

First, a vault should be prepared for the reception of the hides; this, for convenience sake, should be twelve feet long, the same in depth, and ten feet wide. The walls may be of stone, brick, or a planked frame. There should be one alley or vestibule for entrance, not less than six feet long, having a door at each end, the outer being made double and filled in with tan, to prevent the communication of warm dry air from without. A ventiduct made of plank, ten or twelve inches square, should extend from the bottom of the vault to the distance of three or four rods, and should be fixed not less than three or four feet below the surface of the ground. This channel serves both as a drain for discharging the water of the vault, and for admitting cold damp air to supply the place of that which has become rarified, so that a current is thus kept up through the ventilator at the top of the vault. The ridge of the roof may be on a level with the ground, and on it, extending its whole length, are set up edgeways two planks two inches apart. The space between these is to be left open, but the remainder of the roof may be covered with earth to the depth of a yard. Such covering is intended to preserve a low temperature in the pit, so that the hides may unhair without tainting. Spring water should be conducted, either in pipes of logs, around the angles formed by the ceiling with the walls of the vault; and from these conduits the fluid should be allowed to flow in minute jets, so as to form a spray, or else to raise a mist of vapour, so as to saturate the atmosphere of the vault with watery vapour. This arrangement keeps the temperature of the vault much under that of spring water itself, which usually stands at 50°, owing to the heat rendered latent by the evaporation. Three bars furnished with iron hooks, at intervals of three inches, are laid longitudinally and equidistant near the ceiling, and upon them the hides are suspended. Before hanging up the hides, they are soaked as for breaking, and then suspended form the butts in a way that they remain fully open. In the course of a few days, when the hair begins to loosen on the upper parts, they are taken down, and the middle bar being raised, they are again suspended by the other end, and left so till the hair easily separated. The hides should not be broken till they are ready to unhair. In a good vault, where the heat is maintained between 44° and 56°, above which it should never be allowed to rise, and where there is a free circulation of damp air, the hides generally require from six to twelve days. If the temperature falls below 44°, the ventilator should be partially closed; but if it rises above 56°, cold damp air must be forced in, or a larger volume of spring water thrown into the pit.

Morfit states, that the hides carried carefully through this process are, when received by the tanner from the beamsman’s hands, free from extraneous matter, and retain all their gelatine, albumen, and fibrin in an unimpaired state; and that it is not a fermentative change that produces the unhairing, because there is no ammonia generated. The effect is owing to the softening action of the absorbed vapour upon the epidermis, in conjunction with a swelling or distention of the roots of the hair, and tissue of the skin immediately underlaying them. Should these advantages be found, upon trial, attendant upon this simple and quite feasible method, it would undoubtedly be for the interest of tanners to adopt it, as not only does it require less labor, but the requirements in the shape of pits and water are still less than for the systems practised on this side of the Atlantic, leaving the consideration of the great gain in the amount of leather out of the question; and which, of course is its most powerful recommendation.

By Rhusma.—Warington recommends a solution of carbonate of soda for unhairing the hides, but the effect is not so rapid as when the alkali is in the caustic state. The same chemist, in attempting to depilate hides by the use of rhusma, the long-known mixture of caustic lime and orpiment, or tersulphide 14 of arsenic, discovered that the active agent was sulphide of calcium, formed by the decomposition of the arsenical compound in the presence of that base, and that the arsenic was without effect in the operation. He therefore tried the action of sulphide of calcium per se, and found that it acted so promptly, that only from twenty-four to thirty-six hours were required to soften the epidermis, and loosen the hair.

Raising or Swelling.—After the removal of the hair and epidermis, and the bating, in case of hides intended as upper 15 or pliable leather, it is necessary, to submit the pelt, as the depurated 16 unhaired skin is commonly called, to a further operation, in order to distend its cellular organs, with a view of enabling it the more readily to combine with the tannin. In England, sulphuric acid, in the ratio of one part of acid to a thousand of water, is the agent usually employed for this purpose; but in some cases immersion for a limited period in the spent tan-liquor, wherein a certain quantity of gallic and other acids have been developed, is substituted, and even this treatment is abandoned by may, a weak tanning liquor being preferred. This is especially the case in France, where a prejudice exists against the use of sulphuric acid, founded on the opinion that it destroys many of the good qualities of leather. When sulphuric acid is used, the swelling or raising is sufficiently executed by twenty-four hours’ immersion in the bath. When kips and skins are under operation, the raising is done partly during the liming and partly by bating, to which they are afterwards submitted. Allusion has already been made to the mode practised with excrements; but besides this, the same end—the removal of any residuary lime—is attained by the employment of barley meal, made into a sour liquor. For one hundred pounds of dry skin, fifty pounds of coarsely-ground barley meal, and five or six pounds of soured dough are taken, the whole being intimately distributed in the water. Lactic fermentation follows, and the acids generated form soluble salts with the lime in the skins, when the latter are immersed in the liquor, and the succeeding washing removes them. This bath is termed the white bate, to distinguish it from the red bate, or the aqueous washings of old used bark or tan. With this reddish brown liquid a number of vats are filled, the solution in the first being diluted so as to give them a gradation of strength. Before submitting the washed and unhaired skins to the series, they are steeped for a few days in summer, but a longer time—four or five days—in winter, in clean water, which is renewed every day, whilst the skins are left to drain for two or three hours. After this they are submitted to the first and weakest vat of red bate, and after spending some time in it, they are transferred to the next and so on, till they come to the last. During these operations the practice is to handle the skins morning and evening, leaving them to drain about three hours, whilst they are passing through the weak baths; but once a-day when the arrive at the stronger ones. Sometimes, in this way of working, the final bath are a solution of fresh tan, more or less concentrated, according to the views of the tanner. When the baths are rather concentrated, the period occupied in swelling by this method varies from a fortnight to three weeks.

The finishing of the raising is effected occasionally with strong tan-juice, which has been mixed by agitation with about four pounds of sulphuric acid. Eight or ten hides being submitted to this bath, they are taken out the first day twice, and permitted to soak of drain for two hours, the second day once, the same time being allowed for draining. In the morning of the third day they are transferred to another, composed of the densest tan-liquor, mixed with the same quantity of sulphuric acid as the foregoing. Whilst here, the hides are handled once a day, being allowed to drain at each handling one hour. About three days suffice to give them the necessary finish.

The red bate is regarded as being by far the best means in use, notwithstanding it is much slower in its effects than some of the others adopted in practice. This may arise from the fact, that the combination of the gelatinous tissue of the skin with the tannin is slowly going on from the immersion in the first vat of the series, at the same time that the lime is being removed, and, consequently, that the finished leather is more compact, and tougher, than if the swelling were made with acids in a shorter time.

Next Page: the Tanning Process.


1. ^    This is one of the uses to which the output of the salt-makers of the Lincolnshire coast in the Roman and Mediaeval periods will have been put.

2. ^   It is tempting to see this as a form of the French tremper, to soak but it will mean, in origin at least, walking on a vat full of soaking skins, in the manner of a mediaeval fuller, on cloth. The personal name, Walker comes from this latter trade.

3. ^   Fullers would buck cloth by steeping it in alkaline lye in the process of buck-washing, of bleaching (OED).

4. ^   A stock is a tree trunk or post. Again, the process is similar to that of fulling. The stocks would be repeatedly raised by power from such as a water wheel then allowed to fall, so strongly agitating the contents of the vat.

5. ^   This would be a problem in Bourne, where the water comes from the limestone aquifer.

6. ^   In Bourne, lime was produced in the vicinity of Bedehouse bank. For its production see Brees or Muspratt.

7. ^   In Bourne, T.W.Mays had two businesses. One, alongside the former navigation basin, included fellmongery, the preparation of sheep skins. The other, by the South Fen Slype, was a knackery, producing among other things, glue.

8. ^   This word is associated with beating. Here, the quantity of lime is beaten down or abated. (OED)

9. ^   Sugars dissolved in water.

10. ^ A salt of saccharic acid.

11. ^  The action of stripping of hair (OED).

12. ^ Muspratt never specifies his temperature scale but it will be Fahrenheit.

13. ^  This looks like a compositor’s error. It is not a mistake which is readily made in typing but an italic g would readily find its way into the type case with the y’s. It is a reminder of the enormity of the task of composing a work of well over 2,000 pages, letter by letter.

14. ^ Trisulphide. See Arsenic trisuphide.

15. ^  Suited to use in the upper parts of shoes.

16. ^ Made free from impurities (OED).

Link to the Berkeley Laboratory for a modern view of the interaction between a protein and a salt.

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