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A small quantity of these agents, however, may to produce black with oxide of iron, by restoi. sometimes form supercompounds with the stuff, ing this metal to the state of a black oxide, and and its color may be altered in that way. The by their assuming a dark color froin the action of oxides of metals produce in the coloring particles, oxygen. with which they unite, a degree of combustion 76. The notion of an astringent supposes, proportioned to the quantity of oxygen which moreover, the property of combining in a certain these particles can take from them. Therefore quantity with animal substances, giving them the colors, which the compounds of metallic thus solidity and incorruptibility ; because these oxides and coloring particles assume, are the two properties are most commonly united. These product of the color peculiar to the coloring again are derived from their large share of carparticles, and of that peculiar to the metallic ox- bon, a circumstance in their composition which ide: but the coloring particles and metallic ox- gives them increased tendency to solidity, and ides must be considered in that state to which greater stability. they have been reduced by the diminution of ox 77. On this ingenious theory of Berthollet, Dr. ygen in the oxide, and the diminution of hydro- Bancroft, an able writer on dyeing, has made gen in the particles that produce the color. It some remarks that deserve attention. In his follows from this, that the metallic oxides, to opinion M. Berthollet, in ascribing the decays which the oxygen is only slightly attached, are of vegetable and animal coloring matters in not fit to serve as intermedia for the coloring general, to effects or changes similar to those of particles, because they produce in them too combustion, has gone much farther than is wargreat a degree of combustion ; instances of this rantable by facts. It cannot, he thinks, be his kind are the oxides of silver, gold, and mercury. intention, that we should apply the term of The oxides which undergo considerable altera- combustion to alterations which result from a tions of color, by giving off more or less of their simple addition of oxygen to coloring matters, oxygen, are also bad intermedia, particularly for with a destruction or separation of any of their light shades, because they produce changeable component parts; though many of the decays colors; examples of this kind are the oxides of and extinctions of these colors evidently arise copper, of lead, and of bismuth. The oxides only from such simple additions of oxygen. The which strongly retain their oxygen, and undergo nitric, sulphuric, and other acids, containing very little change of color by the loss of a propor- oxygen, have the power not only of weakening, tion of it, are the most suitable for this pur- but of extinguishing, for a time, the colors of pose ; such is particularly the oxide of tin, which many tingent matters; not by any effect which quits its menstruum easily, which has a strong can properly he denominated a coinbustion, but affinity for the coloring particles, and which rather by a change in their several attractions for affords them a basis that is very white, and pro- particular rays of light; but none of their parts per for giving a brightness to their shades, without being destroyed, or carried away, the addition of altering them by the mixture of another color. an alkali, or of calcareous carbonate, will geThe oxide of zinc is possessed of some of these nerally undo such alteration, and restore the properties in a considerable degree.

original color, by decomposing and neutralising 75. To account for the colors, which proceed the acid or oxygen which had caused the alterafrom the union of the coloring particles with the tion. basis which a mordant gives them, we must at 78. Of this numerous instances might be given, tend to the proportion in which the coloring it being the case of almost all vegetable or aniparticles unite to that basis. Thus the solution mal coloring matters. It will be sufficient to of tin, which produces a very copious precipitate mention, that ink dropped into a glass of diluted with a solution of coloring particles, and which nitric, vitriolic, or other acid, will lose its color, thereby proves that the oxide of tin enters in a and that it may be again restored by adding a large proportion into the precipitate, has a much suitable portion of vegetable or fossil alkali; and greater influence on the color of the precipitate, that this may be done several times with the same by the whiteness of its basis, than the solution of ink, and therefore the change, or loss of color, zinc, or that of alum, which generally produce could not have been the effect of combustion. much less copious precipitates. The precipitates If, however, this ink had not been fixed by dyeproduced by these two last substances retain ing in the substance either of wool, silk, linen, very nearly the natural tint which the coloring or cotton, and the substance so dyed had been particles afforded. It is therefore necessary to dipped into a glass of diluted acid, a considerdistinguish, in the action of mordants, the com- able part of the coloring matter woulů have been binations that may take place by their means, be- dislodged, aud separated from the dyed subtween the coloring particles, the stuff, and the stance, by its affinity with the oxygen or acid; intermedium; the proportions of the coloring although no combustion had taken place, the substances and intermedium; the modifications color so separated and lost could not be again of color, which may arise from the mixture of restored without a second dyeing. This loss o the color of the coloring particles, and of that color would be similar to what frequently hapof the basis to which they are united ; and the pens to colors from exposure to the sun and air, changes which the coloring particles may suffer, by which they are gradually weakened, many of from the combustion that may be produced by them without any other change of tint than the the substance that is employed as an interme- simple diminution of their original quantity of dium. It is evident also, that astringents do not coloring matter; and this continuing in the more differ essentially from coloring particles; but the fugitive colors, particularly that of turmeric

, the 'atter take this vame, especially when employed cloth is soon left as white as before it had beeu

dyed, without any thing like combastion having 80. Dr. Bancroft is also of opinion, that the ever taken place in it, or in the matter with blue color of indigo depends upou a certain which it was dyed. It may also be presumed, portion of oxygen, for he has found that a soluthat colors are not generally impaired by any tion of indigo, by losing its oxygen, may become thing like combustion, from this fact, that there as pellucid, and, excepting a very slight yellowish are but few of them which the common muriatic tinge, as colorless as water, and afterwards acid does not injure, as much as either the nitric speedily return through all the shades of yellow or the sulphuric; and as there can be no combus- and green to its original deep blue, by exposure tion without oxygen, and as the common muriatic to atmospheric or vital air. Similar to this, bu acid either contains none, or what it does contain remarks, is the fact long since observed by the is confessedly combined with it by an affinity too abbè Nollet, of the tincture of archil employed powerful to be overcome by any known substance to color the spirit of wine used in thermometers, or means, it follows, that the oxygen (if it contain and which after some time loses its color, but any) cannot be liberated so as to act in the way of recovers it again upon being exposed to atmoscombustion upon any other matter; and therefore, pheric air. This also happens to the infusion when the common muriatic acid changes or de- of turnsole, and to syrup of violets, which lose stroys the colors, it changes or destroys the af- their colors when secluded from air, aud regain finities upon which they depend, by producing them when placed in contact with it. He has effects different from those of combustion; and also observed various animal and vegetable coas the changes which it produces on colors are lors, produced solely by the contact of atmosin most cases similar to those produced by the pheric air; and some others, which, when given nitric, sulphuric, and other acids known to con- by dyeing or callico-printing to wool, silk, cottain oxygen, ii is reasonable to conclude, that ton, &c., though unable to sustain a single day's these also act upon colors, by producing other exposure to the sun and air without manifest effects than those of combustion.

injury, were found to receive none from the 79. M. Sennebier exposed a great variety of action of strong nitric or sulphuric acids, but, woods to the action of the sun and air, and found on the contrary, were perceived by being wetted ail their colors very soon affected. The white with them, and even with oxygenated muriatic woods generally became brown, and the red and and sulphuric acids. But the same colors, if coviolet changed either to yellow or black. Guaia- vered with linseed oil, were found to decay more cum was rendered green; the oak and the cedar quickly from exposure to the sun and air, than were whitened, as were the brown woods gene- if uncovered. These colors, therefore, he conrally; effects which certainly do not resemble tends, could not owe their decay to the contact those of combustion, any more than the bleaching or combination of oxygen, because they were of wax or tallow by exposure to the air. It is not only unhurt, but benefited by its concentrated therefore evident, argues Dr. Bancroft, that the powers in the nitric, the oxygenated muriatic, and color of each particular substance depends on sulphuric acids; and also because they were its constitution, producing in it a particular at soonest impaired when defended from the access traction for certain rays of light; and a disposi- of oxygen, by being covered with linseed oil. tion to reflect or transmit certain other rays; and Probably the decays of these colors were occain this respect it may doubtless suffer very con- sioned hy a loss of at least some part of the siderable changes from the action or combination oxygen which was necessary to their existence, of oxygen, without any effects similar to those and which the linseed oil assisted in depriving of combustion. And, indeed, the changes of them of, hy the strong affinity it has with oxygen. color which arise from the access of atmospheric 81. Dr. Bancroft further observes, that, in air, seldom resemble those which the mere pre- forming systems, we are apt to draw general dominance of blackness (the supposed natural conclusions from only a partial view of facts. color of carbon) would produce; though this This M. Berthollet seems to have done, not may have been the case with the coloring matter only in ascribing the decays of vegetable and of brown or unbleached linen, upon which the animal colors, exclusively to effects similar to experiments of M. Berthollet seem principally to those of combustion, but also in representing have been made. But whether the action of the oxygenated muriatic acid, as an accurate test vital air, or its basis, in promoting the decays and for anticipating, in a fe v minutes, the changes colors, ought to be denominated a combustion or which these colors are liable to suffer by long exnot, Dr. Bancroft is confident, that at least some posure to the action of sun and air; for, says he, of them are liable to be impaired, not so much though it is true, that the oxygenated muriatic by an accession of oxygen, as by the loss of it. acid, in weakening or destroying colors, gives The difference of color in arterial and venous up to them more or less of the oxygen which it blood had been long noticed, and numerous ex had received by distillation from manganese; periments have shown that the fine vermilion co- and that, by this new combination of oxygen, lor of the former is produced solely by vital air, those affinities for particular rays of light, upon which it is capable of acquiring through bladders, which their colors depend, are liable to be dethe coats of blood-vessels, &c. And Mr. Hlassen- stroyed; it is nevertheless true, that the changes fratz seems to have proved, that, as this fine red of color so produced are no certain indication color is gained hy a dissolution of oxygen in the of those, which the combined influence of light arterial blood, so it is lost, and the dark color of and air will occasion upon colors in general ; the venous blood restored, by a separation of there being several colors which are very speedily the oxygen, in consequence of its forming a new destroyed by the latter of these causes, though combination with the hydrogen und carbon of they resist the strongest action of the oxygenated the same.

muriatic acid, without suffering any degree of

injury or hurt. The Dr. adds, that M. The first two, independently of the azote, pos Berthollet well knows, since nobody has con sess a marked difference of composition, from tributed more to ascertain, how much the pro- their excess of carbon and deficiency of oxygen. perties of oxygen are diversified by each par 85. In consequence of this composition, ticular basis to which it unites; and that it does animal substances, when set on fire, produce a not, therefore, seem warranta'le to imagine, that bright Aame, which breaks out at the beginning, its action will not be modified by a basis so but is soon stified by the charcoal which is powerful as that of the common muriatic acid, formed, and which has peculiar properties; their or that the united properties of both should re combustion is accompanied with a penetrating present or resemble those of atmospheric air odor, owing to the ammoniac and oil which upon colors, any more than they do in the lungs escape unconsumed ; they are liable to putreby respiration; where, instead of supporting faction, in which process ammoniac is produced, life, they would instantly put an end to it. as well as in their distillation, by a more intimate

82. These observations were made in reference union of the azote and hydrogen ; while vegeto the manner in which M. Berthollet had ex table substances, on the contrary, undergo the pressed himself on the subject in his Elemens vinous and acetous fermentation. It is evident, de l'Art de la Teinture, published in 1791. A that, as animal substances contain a considerable new edition of this work was published about quantity of principles disposed to assume an the year 1804, in which the author has fully elastic form, they have less cohesive force among noticed Dr. Bancroft's arguments; refuted some their particles than vegetables, and a greater disof them; admitted the force of others in part; position to combine with other substances; hence and, in some respects, has availed himself of they are more liable to be destroyed by different the important improvements of Dr. Bancroft. agents, and are more disposed to combine with

coloring particles. OF THE DIFFERENCES BETWEEN ANIMAL AND

86. The consequence of this action on animal VEGETABLE SUBSTANCES.

substances is, that they cannot bear lies, and 83. Before we proceed to treat of the practice that alkalis should be used with great caution in of dyeing, it will be necessary to consider some the processes employed for dyeing them; whereof the leading differences that exist between as no danger is to be apprehended from the use several of the substances to be dyed, and to of alkalis with substances of the vegetable kind. point out the processes through which they must Nitric and sulphuric acids have also a consi pass before they will receive the colors required. derable action on animal substances : the former The following is the substance of M. Berthollet's decomposes them, extricates the azote, separates opinion relative to this subject :— It is now known, the fatty matter, and forms carbonic acid or that the composition of animal substances is fixed air, and oxalic acid or the acid of sugar distinguished from that of vegetables, by their with a part of the hydrogen and a part of the abounding in a particular principle called azote, charcoal; the latter extricates the inflammable which is found only in small quantities in vege- gas, probably azotic gas, and reduces the other tables, as well as by their containing much more principles to the state of carbon. Silk bears hydrogen, or base of inflammable air, than is some resemblance to vegetable substances, from found in the other. From these two causes, the its being less disposed to combine with coloring differences observed in the distillation of animal particles, and by resisting the action of alkalis and vegetable substances proceed: the former and acids more powerfully; which may arise yield a large quantity of ammoniac or volatile either from the same principles being more intialkali; the latter afford very little, and some- mately combined in it than in wool, or, more times yield an acid: the former yield a great probably, from its containing less azo:e and deal of vil, the predominant principle in which hydrogen. But, though the action of alkalis and is hydrogen, which is very volatile and disposed acids upon silk be weaker than upon wool, they to fly off by a small increase of temperature; should still be employed with great caution, bewhile the latter sometimes do not yield it in the cause the brightness of color required in silk least sensible quantity.

appears to depend upon the smoothness of its 84. Dr. Ure in a note, p. 151, vol. I. of his surface, which should, on that account, be pretranslation of Berthollet's treatise, has the fol- served unimpaired, with every possible attention. lowing remarks on this theory. Modern re- Cotton withstands the action of acids much betsearches do not justify this position of M. Ber- ter than flax or hemp. Even the nitric acid does thollet. Sugar and starch, by the analyses of not destroy it without great difficulty. M.M. Gay Lussac and Berzelius, contain about

OF Wool. as much hydrogen as fibrin does, and very little less than gelatin and albumen; while, by my

87. The value of wool, and its fitness for the analyses, wool and silk contain less hydrogen different kinds of manufacture, depend upon the than cotton and fax. See Phil. Trans. for length and fineness of its filaments. Wool is 1822.

naturally covered with a kind of grease, which I subjoin the results of my analytical experi- preserves it from moths ; so that it is not scoured ments on the four principal subjects of dyeing.

until it is about to be dyed, or formed into yarn.

To scour wool, it is generally put for about a Carbon. Hydrogen. Oxygen. Azote. quarter of an hour into a kettle, containing a Wool 53.70 2.80

sufficient quantity of water, mixed with oneSilk 50.69 3.94 34:04 11:33 fourth of putrid urine, heated to such a degree Cotton 42:11 5.06 52.83

as the hand can just bear, and it must be stirred Flax 42.81 5:50 51.70

from time to time with sticks. It is then taken

31.20

12.30

cesses.

out, put to drain, and carried in a large basket and they be rubbed against each other in the to a running water, where it is moved about longitudinal direction of the hair, it acquires a until the grease is entirely separated, and no progressive motion towards the root. This eflonger renders the water turbid; it is afterwards fect depends not on the nature of the skin of the taken out, and left to drain. It sometimes loses finger, or on its texture, for if the hair be turned in this operation more than a fifth of its weight. and the point placed where the root formerly This operation should be conducted with much was, the motion is reversed, that is, it will still care, since the more correctly it is performed, be towards the root. the better is the wool fitted to receive the dye. 90. On this peculiarity of structure, which In this process the ammonia or volatile alkali was observed by M. Monge, depend the prowhich exists in the urine, readily combines with cesses of felting and fulling of hair and wool the oil of the woul, and forms a soap, which, for different purposes. In the process of felting, being soluble in water, is dissolved and carried the flocculi of wool are struck with the string of off.

the bow, by which the filaments are detached, 88. Wool is dyed in the fleece before it is and dispersed in the air. These filaments fall spun, when it is intended to form cloths of mixed back on each other in all directions, and, when a colors; it is .dyed after being spun, when in- layer of a certain thickness is formed, they are tended principally for tapestry: but it is most covered with a cloth, on which the workman generally dyed after having been manufactured presses with his hands in all parts. By this into cloth. If wool be dyed in the fleece, its pressure the filaments are brought nearer to each filaments, from being separate, absorb a larger other; the points of contact are multiplied; the quantity of the coloring particles than when it progressive motion towards the root is produced is spun; for the same reason, woollen yarn takes by the agitation; the filaments entangle each ap more than cloth: but cloths themselves vary other; and the laminæ of each taking hold of considerably in this respect, according to their those of the others, which are in an opposite degree of fineness, or the closeness of their tex- direction, the whole is retained in a state of close ture. Besides, the variety in their dimensions, contexture. the different qualities of the ingredients employed 91. Connected with this operation is that of in dyeing, and a difference of circumstances in fulling. The roughness on the surface of the the process, prevent us from relying 'upon the filaments of wool, and their tendency to acquire precise quantities recommended for the pro a progressive motion towards the root, produce

This ought in all dyes to be attended to. great inconvenience in the operations of spinning It is a fact well known to dyers and others, that and weaving. This inconvenience is obviated the coarse wool from the thighs and tails of by covering the filaments with a coat of oil, some sheep receives the coloring particles with which fills up the pores, and renders the asperities great difficulty. The finest cloth is never fully less sensible. When these operations are finished, penetrated with the scarlet dye, hence the in- the stuff must be freed from the oil, which would terior of the cloth appears always of a lighter prevent it from taking the color with which it is shade when cut, and sometimes almost white. to be dyed. For this purpose it is taken to the For the generality of colors, wool requires to be fulling-mill, where it is beaten with large beetles, prepared by a bath, in which it is boiled with in a trough of water, through which clay has saline substances, principally with alum and been diffused. The clay unites with the oil, tartar ; but there are some dyes for which the which, being thus rendered soluble in water, is wool does not require such a preparation; then carried off by fresh portions of water, conveyed it must be well washed in warm water, and to it. In this way the stuff is scoured; but this wrung out, or left to drain.

is not the sole object of the operation. By the 89. The surface of the filaments of wool or alternate pressure of the beetles, an effect similar hair is not quite smooth; for, although no rough- to that of the bands of the work man, in the ness or inequality can be discovered, yet they operation of felting, is produced. The filaments seem to be formed of fine laminæ placed over composing a thread of warp or woof, acquire a each other in a slanting direction, from the root progressive motion ; are entangled with the of the filament towards the point, resembling the filaments of the adjoining threads; those of the arrangement of the scales of a fish, which cover latter into the next, and so on, till the whole beeach other from the head of the animal to its come felted together. The stuff is now con'ail. This peculiarity of structure is proved by tracted in all its dimensions, and, participating a simple experiment. If a hair be held by the both of the nature of cloth and of felt, may be root in one hand, and drawn between the fingers cut without being subjected to ravel ; and, when of the other hand, from the root towards the employed to make a garment, requires no hempoint. hardly any friction is perceived, and no ming. In a common woollen stocking web, poise is heard ; but if it be seized by the point, after this operation, the stitches are no longer and passed in the same manner between the subject to run, and, the threads of the warp and Singers from the point towards the root, a re woof being less distinct from each other, the sistance is felt, and a tremulous motion is per- whole stuff is thickened, and forms a warmer ceptible to the touch, while the ear perceives a covering slight noise. Thus it appears, that the texture

OF SILK. is not the same from the root towards the point, as it is from the point towards the root. This is 92. Silk in its natural state is coated over farther confirmed by another experiment. If a with a substance which has generally been conhair be held between the thumb and fore-finger, sidered as a kind of gum or varnish. To this

substance the silk is supposed to owe its elasticity silk that degree of brightness which is necessary, and stiffness. Besides this varnish, the silk when it is to be employed in the manufacture of usually met with in Europe is impregnated with white stuffs. For this purpose it must undergo a substance of a yellow color, and, for most the process of sulphuration, in which the silk is of the purposes for which silk is required, exposed to the vapor of sulphur. But before it is necessary to free it from both the varnish the silk which has been thus treated is fit for reand the coloring matter. To effect this, the ceiving colors, and retaining them in their full silk is subjected to the operation of scouring; lustre, the sulphur which adheres to it must be but it is very obvious that when the silk is to be separated by immersion and agitation for some dyed, the scouring need not be carried so far time in warm water, otherwise the colors are as is required where it is to remain white. Dif- tarnished and greatly injured. ferent colors, also, will require different degrees 97. It has long been an object of considerof scouring; 'and this difference is generally able importance, to deprive silk of its coloring regulated by the quantity of soap employed : matter, without destroying the gum, on which 105 pounds of silk boiled in a solution of its stiffness and elasticity depend. A process twenty pounds of soap, for three or four hours, for this purpose was discovered by Beaume, but, supplying a little water occasionally because of as it was not made public, others have been led the evaporation, will be sufficiently prepared to to it hy conjecture and experiment. The followreceive the common colors. For blue colors the ing account, given by Berthollet, is all that has proportion of soap must be greater; and scarlet, transpired concerning this process. A mixture cherry color, &c., require a still greater propor- is made with a small quantity of muriatic acid lion, because for those colors the ground must be and alcohol. The muriatic acid should be in a whiter.

state of purity, and entirely free from uitric 93. When silk is to be employed white, it acid, which would give the silk a yellow color. must undergo three operations. The first con In the mixture thus prepared, the silk is to be sists in keeping the hanks of silk in a solution immersed. of thirty pounds of soap to 100 of silk: this 98. One of the most difficult parts of the solution ought to be very hot, but not boil- process, especially when large quantities are ing; when any part of the hanks immersed is operated upon, is to produce a uniform whiteentirely free from its gum, which is known by ness. In dyeing the whitened silk, there is also the whiteness it acquires, the banks are to be some difficulty in preventing its curling; hence, shaken over, as the dyers term it, so that the it is recommended to keep it constantly stretched part which was not before immersed, may during the drying. The muriatic acid seems to undergo the same process. They are then taken be useful in this process, by softening the gum, out and wrung, as the process is finished. and assisting the alcohol to dissolve the coloring

94. In the second operation the silk is put particles which are combined with it. The alinto bags of coarse cloth, each bag containing cohol which has been impregnated with the from twenty-five to thirty pounds. A solution coloring matter may be again separated from it of soap is prepared as in the former case, but and purified, and may thus serve in future opewith a smaller proportion of soap. In this the rations, and render the process more economical. bags are boiled for an hour and a half; and that This may be effected by distillation with a mothey may not receive too much heat by resting derate heat, in glass or stone-ware vessels. on the bultom of the vessel, they must be con The preparation with alum is a very important stantly stirred during the operation.

preliminary operation in the dyeing of silk. 95. The third operation is to communicate without this process, few colors would have to the silk different shades, that the white may either beauty or durability. Forty or fifty pounds be rendered more pleasing. These shades are of alum, dissolved in warm water, are mixed in known by different names, as China-white, silver a vat, with forty or fifty pails of water; and, to white, azure-white, or thread-white. For this prevent the crystallisation of the salt, the solution purpose a solution of soap is also prepared, of must be carefully stirred during the mixture. which the proper degree of strength is ascer- The silk being previously washed and beerled, tained by its manner of frothing by agitation. to separate any remains of soap, is immersed in For the China-white, which is required to have this alum liquor, and after eight or nine hours is a slight tinge of red, a small quantity of anatto wrung out, and washed in a stream of water : 150 is added, and the silk is shaken over in it till it pounds of silk may be prepared in the above has acquired the shade required. In other quantity of liquor; but when it begins to grow whites, a blue tinge is given by adding a little weak, which may be known by the taste, twenty blue to the solution of soap. The azure-white or twenty-five pounds of alum are to be added, is produced by means of indigo. To prepare and the addition repeated till the liquor acquires the azure, fine indigo is well washed in mode- an offensive smell. It may then be employed in rately warm water, after which boiling water is the preparation of silk intended for darker colors, poured upon it. It is then left to settle, and the till its whole strength is dissipated. This prepaliquid part only, which contains the finer and ration of silk with alum must be made in the more soluble parts, is employed.

cold; for when the liquor is employed hot, the 96. Some use no soap in the third operation, lustre is impaired. but, when the second is completed, they wash

OF COTTON. the silks, fumigate with sulphur, and azure them with river water, which should be very pure. 99. Cotion is the down or wool obtained from But all these operations are not sufficient to give the pods of the gossipiun, a shrubby plant which

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