AN ESSAY ©N THE THEORY AND PRACTICE OF WHEREIN THE SULPHURET OF LIME IS RECOMMENDED AS A SUBSTITUTE FOR POT-ASH. By william HIGGINS, m.r.i.a, JROFESSOR OF CHEMISTRY AND MINERALOGY AT THE REPOSITORY OF THE DUBLIN SOCIETY. lonlKm: PRINTED FOR THE AUTHOR; , AND SOLD BY ■ , VERNOR AND HOOD; NO. 31, POULTRY. 1799. rmcE TWO shillings. \ ■ 4 -A TO THE RIGHT HONORABLE and HONORABLE THE LINEN BOARD, THE FOLLOWING '■ E S S A T IS INSCRIBED BY THElk MUCH OBLIGED, ANP VERY HUMBLE SERVANT, THE AUTHOR . r V ”> *■> f': iA A, ^ , I . atic acidy and on the methods of pre^ . paring it - - , - 34 SECTION IV. On the fulphiiret of lime^ as a fubjlitute for poUaJh - .33 SECTION V. ■ On bleaching with the fulphuret of lime 6 o 1 * PREFACE, Soon after I fent in a report on the fulphuret of lime to the' tinen Board, they requefted' to have fome experi- ments made upon it in their prefence, at the Elaboratory of the Dublin Society in Hawkins’s-ftreetj which led to a leftiire upon the general principles of bleaching, illuftrated with fuitable experinaents. At that time, I had no idea of pub- lifhing any thing upon the fubjefl j but finding. that it was the with of the ^t. Hpn. John Foft^r, Speaker of the Houle • Vlll PREFACE. Houfe of Commons, and of the Rt. Hon. Ifaac Corry, who were prefen t, ' to have it printed for the ufe of the bleachers, I readily affented, feeling great fatisfaftion in having it in my power to comply with the wi/hes of hefe gentlemen, but particularly with the wifh of the man ^ who has fo ma- terially contributed to the prefent profperous Rate of the Linen Manu- facture of this kingdom, and who fo. difmtereftedly makes it his ftudy to forward every other manufacture and inftitution likely to be productive q( national good. I alfo undertook the talk with fame degree of alacrity, when I confidered that any treatife likely to throw light upon the principles of this art, muft not only be acceptable^, but ultimately of infinite . * The Rt. the Speaker. PREFACE. ix infinite fervice to the bleacher, whbfe procefsis truly chemical in allitsftages; When I firft fat down to write, I intended to confine myfelf to the mere bleaching of the cloth by means of the oxygenated muriate of lime, and the fulphuret of lime \ but I afterwards con- ceived, that it would be much better to give a full narrative and theory of the whole procefs in the old and new me- thod, and alfo, to commence with the green flax fo as to begin at the right end of the chain, and to avoid chafms, to take it up link after link, according to the pofition or arrangement which the finger of nature feemed to point out to me. In fo fliort an eflay confined to the one obje<5i:, this could be no difficult talk j however, I will obferve, that in b all X PREFACE. allfcientifi'c works, much depends upon good arrangement, for without it, there can be no peripicuity j and as chemiftry embraces fuch a vaff field, indeed I may fay, all the materials of this globe, and moft of the phcenomena which come within our reach, in no one branch of fcience is arrangement mpre neceflary, or more difficult to be ac- complifhed. As the following effay was written for the ufe of the bleachers only, and as the majority of them are not well acquainted with the theory of cheniif- try, I have endeavoured to write it in as fimpleand familiar a ftile as the nature of the fubje6l would admit : I have overlooked minutiae altogether unne- cefsary to the bleacher, which, I fhould hope, the man of fcience will excufe. " The PREFACE. XI The few technical terms, which I was obliged to ufe, areexplained at .the bot- tom of the page, which I confidered more convenient to the reader than to have them fet apart by themfelves. I now beg. leave to fay a few words to my philofophical friends. Nine years have elapfedfmce laddrefled them laft^ at that time, when I publifhed my Comparative View^ the controverfy ran very high between the Phlogijiians and the AntiphlogiJUans. For a confiderable- time have I flood alone in England, where I then refided, being the firft who adopted the antiphlogiftic doc- trine, and the only man who had ex- prefsly written in favour of it in the Englifli language. During this interval, nothing worthy of notice has appeared for or againfl' either PREFACE. XU either do6lrine, and now, the antiphlo-s giftic theory is received by all the phi- lofophers of Europe, at leaft, by thqfe who deferve the name, of philofophers. I have fe^n, with pleafure, that,fince the controverfy was laid afide, and the true theory of chemiftry adopted and fixed upon a firm bafis, moft chemical philofophers have applied their know- ledge and talents to the improvement of the arts andmanufaflures, which is the ultimate andgrandobjefl of thefcience. I have feen alfo, with great aftonifli7 ment, that fome experiments which I made and publiflied, were a confiderr able time afterwards adduced as new, difcoveries on the contine:nt. Firft, Monfieur Fourcroy the year 1791*, as a new difcovery, the * Set Medecin tclaire par Its fciencts phijiques Tom, 2d. pag. 321. No. X i. PREFACE. Xlll the prefence of bile in the blood ; or rather, the converfion of fome of the principles of the blood into a fubftance refemblingbile: This I had done fome years before him by the mediation of the nitrous acid. For the truth of what I affert, fee pages 162 and 163 of my Comparative View, publifhed in the year 1789. Secondly, Monjieur Vanquilin has publifhed as his difcovery, in the "Jour- nal des Mines a new method oj de-^ termining the quantity of carbon contained in feeli' See the extra6l from it in the Annaks de Chemie for the year 1797, This new method is by means of the volatile fulphurequs acid, and for the " - difcovery I will refer to my Comparative View, pages 49, 50 and 51, where the juftice of my claim will evidently ap- pear. I by XIV PREFACE. I by no means impeach the above philofophers with plagiarifm ; I 'have too much refpeft for the liigh charac- ter they have acquired in the fcientific world to fufped: them of fuch condu6l> , but that' it has been, at lead, an over- fight, muft be allowed. ‘The chemical properties of the ful- phureous acid were very, little known, if at all, when I publidied my experi- ments upon the fubjecV. It firft drew my attention with a view folely of in- veftigating the truth of th^antiphlogi/lic theory, and it furnilhed me with mcon^ trovertible arguments in favor of that do6lrine. Amongft its various proper-, ties, that of diffolving iron without the produElion of hydrogen gas, at the fame time that the ^hole of the carbon and fulphur contained in the iron were left behind,. PREFACE. XV behind, impreffedme mofr, by pointing out the importance of it as a rnenjlriium • for the analyfis of iron or fteel in an eafy, fimple, and certain way. The celebrated Bergman laboured hard to ‘analyfe the different kinds of iron and fteel, and made the moft of the menftrua which the chemiftry of his days afforded : Heafcertainedonly the prefence of thofe fubftances con- tained in iron \ nor was it poflible to find out their proportion by any means hitherto difcoVered, until the happy ^ application of the fulphureous acid in that way. Sulphuric acid confifts of one.part of fulphur, and two of oxygen chemically united. When iron is introduced into this acid diluted with four or five times ' its bulk of water, it is diffolved, and ' hydrogen XVI PREFACE. hydrogen gas Is copioufly produced, which Is now allowed to come from the water. The fulphureous acid contains but equal parts of oxygen and fulphur*, that is, one half the quantity of oxygen which the fulphuric acid contains, and yet it'diffolves the iron without the 1 decompofition of water. Thefe two faffs contrafted, opened to my view quite a new theory, which I have al- ready fubmitted to the opinion of the fcientific w orld, and as an explanation of it would be too long for my prefent liniits, 1 will refer to my Comparative F/Vto, from page 36 to page 6 1. Let us now confider how far the French method of accounting for the decompofition of water may be recon- ciled to the above faffs. The *■ This I have fliewn by experiment. See my Comparative, Vicw^ pages 80 and 81. PREFACE. XVll The French philofophers fuppofe, from the attra6lIon of fulpuric acid for an oxyd of iron, that this metal decompofes the water in order to oxygenate itfelf, at the inftant of its union to the acid, and thus liberates its hydrogen : This, they tell us, takes place, by virtue of a predifpofing affi- nity: that fuch an affinity exifts, I know by experience 5 but it does not prevail here^, for the fulphureous acid, as containing kfs oxygen, and confe- quently having ftronger affinity to me- tallic oxyds, fliould, upon the above principle, be a more powerful agent In decom- * The brilliant experiment of Mr. Tennant, of Cambridge, by which he decompofed carbonic acid gas, by palTing the vapour of phofphorus through heated carbonate of lime, the oxygena- tion of iron pyrites, and the formation of nitrous acid, from the union of the azote and oxygen of the atmofphere by calcareous matter, are all llriking inftances of this kind of affinity. C Xviii PREFACE. deconipofing water than the fulphuric add. Other theorifts again tell us, that the fulphuric acid unites firft to the iron, and that the, compound decom- pofes the water. But fhould not the compound refulting from iron and ful- phureous acid, as containing one half lefs oxygen, produce the fame effeft?, Even a man who is not a chemift-muft fee the inconfiftency of fuch a doftrine. It would be impoffible to deteft the fallacy of the above theory without the aid of the experiment of the fulphu- reous acid, which {hews that abftracled reafoning, be it ever fo plaufible, is not to be relied upon. The phcenomena of day and night might appear equally well explained by fuppofing the fun to revolve round the earth, as the earth to turn round upon its own axis, every twenty-four hours; were PREFACE. XIX were our knowledge of aftronomy con- fined to thofe circumftances alone 5 but it is by extending our views to the mo- tion and harmony of the whole plane- tary fyftem, that the delufion of fuch a dodlrine can only be detefted. It is juft fo with chemiftry; the concatenating a few fafts here and there, is not fufficient to eftablifh a doftrine^ it is neceflary the theorift fhould traverfe the whole field, accurately examine all the fadls upon record, find out their proper po- fitidn and relation to each other, and fee the arrangement, harmony, and fymmetry of the whole fuperftrudlure at'one'viewj for that dodlrine muft be falfe which contradicts itfelf in any one fingle point. The theory of the decompofition of water during the aftion of acids upon the XX PREFACE. the metals, is not the only inftance in which I differ from the French che- mifts; I only adduce it as being con- ne6led with the difcovery of the ful- phureous acid, as* a menftruum for the analyfis of fteeL ' Indeed, except that alone of the nonentity of phlogifton, our, mode of reafoning is very different. They have ajferted the truth I will allow, but that in an abftrafted and unconnefted man- ner, without fufficient conviftion, for all the phoenomena or fafts adduced feemed equally well explained upon the phlogiftic principle. I have conned:ed the whole, and re- duced it to a fyffem, and made ufe of demonffrations, which in my opinion are not to be invalidated or contra- di 6ted, until the order of natural things affume a different afpedl. ' Some PREFACE. XXI Some of my readers may probably fuppofe, before they enquire Into this fubjedl, that I exaggerate in my own behalf: But affumed modefty upon fuch an occafion as this, would be weaknefs indeed, and affefled diffi- dence downright folly. Every man who writes fhould deli- berately weigh his opinions In the fcale ' of his own underflanding, and be con- vinced according to his judgment that he is right, before he prefents them to the public. Every liberal minded man fliould alfo be open to conviftion, and feel apleafure in having his errors cor- rected : but until this happens, con- fidence and firmnefs are juftifiable. I will now conclude by obferving, that one modification of the antiphlo- giftic doctrine efcaped the French theo- rifts XXII PREFACE. rifts altogether; viz. the decompafitioit and recompofition of water during the oxygenation of metals, and I may add, other inflammable bodies, in the com- mon temperature of the atmofphere. This I have fhewn by experiment, with a view^, principally, of proving the conftituent principles of water, which were dlfputed at the time. I fhall give the following fliort extrad of it from / my Comparatiye View^ psge 13. “Iron moiftened with water, and confined by mercury in a glafs cylinder, v/ill yield inflammable air ; iron, . treated in the fame manner, and confined with de- phlogifticated air, will produce no in- flarnmable air, but the air will be di- minifhed. Iron will yield no inflam- mable air if it be confined in very dry dephlogifticafed air, neither will the ' air PREFACE. XXIII air be diminifhed, nor will the iron tarnifh, in any length of time; hence it appears, that iron has no effeft on air in a common temperature, but that it is the water which is decompofed, and that the dephlogifticated air and the inflammable air of the water unite at the very inftant of the liberation of the latter, and recompofe water.^” From the. foregoing data, it is evi- dent that the decompofition of water does not take place here, in confe- quence of a double affinity occafioned by the oxygen gas, as the iron alone decompofes it, and liberates its hydro- gen in a gaffeous {fate. That a metal fhould take oxygen , from hydrogen with more facility than from . * When the above extraft was pubjifhed, the new nomenclature was net adop.ed. XXIV^ PR E FAC t. from caloric, which retains it with lefs force, proceeds from two concurring and oppofite caufes, viz. the aggregate a'ttradlion of the ultimate particles of the metal to each other on the one fide, and on the other, partly from the affi- nity of oxygen to caloric, but princi- pally from the dlftance by which the atmofpheres of caloric round each par- ticle of oxygen keep them from the furface of the metal, in a word, they are by thefe means kept beyond the ftriking diftance of their mutual at- traftion. By way of analogy, I will adduce a fingle faft to illuftrate this point. — It is well known, that marine acid has very ftrong affinity to cal- careous earth, and yet perfedlly pure and dry calcareous earth will not con- denfe dry marine acid gas, when both are confined in a glafs cylinder over mercury. P3.EFACE. XXV mercury, but as foon as a fmall quan- tity of water is introduced, the gas is condenfed, and then unites to the cal- careous earth. ^ Although water Condenfes the ma- rine acid gas, it has lefs affinity tOL it by much than the calcareous earth, for firi6lly fpeaking, water and marine acid gas do not form a chemical union. I am inclined to believe that the affinity, or rather the capacity of water for caloric, and its attradlion to the gravitating. matter of the marine gas at the fame time, although very weak, co-operate with each other in producing the effecl. I alfo fufpe6t, that a predifpofed affinity of water for a portion of the caloric of the oxygen gas, affifts the hydrogen, in its nafcent ftate, to condenfe it fo as to conftitute water, d The XXVI PREFACE. The rapid and eafy condensation of. oxygen gas by nitrous gas, (which have but a weak attraftion to each other) in the common temperature of the atmofphere, takes place upon the ■ fame principle, and is a ftriking in- ftance of this kind of affinity proceed- ing from caloric, for the compound (jiitrous acid) retains .the whole of the caloric of the oxygen gas in its con- denfed ftate. I am confident the agency of caloric in this way, isr more general than chemifts are aware of. ' From the above flatement, the cir- cumftances which oppofe the union of metals to oxygen gas are very ob- vious : But that metals, when the ag- gregate influence of their particles upon each other, (being the principal obftacle) is removed by caloric, are capable PREFACE. xxvii capable of decompofing oxygen gas, and uniting direftly to its bafe or gra- vitating matter, might be proved by a variety of well connected fafts, were it confidered necefiary. About four years ago, a very ingeni- ous pamphlet appeared in the name of a Mrs. Fulhame, in which this dodtrine of mine refpedling the decompofition and recompofition of water has been adduced and extended to every fpecies of oxygenation, and even to the de- oxydation of metals in every degree of heat. I did not think myfelf warranted when I had written, and much lefs fo now, upon a more mature delibera- tion, to apply it in that general way. Had this fair author read my book, and indeed I fuppofe (he did not, (hav- ing quoted every other treatife upon the XXviii PREFACE. the fabjeft,) no doubt flie would have been candid enough to do me the juftice of excepting 7 ne from the reft of my co-operators in fcience, when flie told them they erred for having over-, looked this modification of their doc- trine, and alfo when fhe adduced it as an original idea of her own. ■ As to the ' reduftion of metals, I have faid fo much already upon it, I have fcarcely any thing to add, for I have confidered the fubjeft in every poffible, point of view, not excepting the agency of hydrogen in its nafcent ftate, when water is decompofed in contaft with thofe oxyds which retain the oxygen with lefs force than hydro- gen attracts it, as the following para- graph^, taken from my Co7nparative View, page 280, will fhew. “ But PREFACE. XXIX But as water is prefent, a portioii “ of it is alfo decompofed, by which means we obtain inflammable air. “ Whether the inflammable air itfelf at the inftant that' it is deprived of “ its dephlogifticated air, may not con- “ tribute to the redu6lion of the mer- cury, by uniting to its dephlogifti- cated air, and reproducing water, is ‘‘ what I cannot pretend to determine; ‘‘ although from the attradlion of the matter of light inflarnmable air to “ fire, together with the interference “ of the Pruflian acid, I am rather in- dined to fuppofe it does not.”^ Although I do not agree with Mrs. Fulhame, as to the decompbfition of water ^ This relates to the reclu£Hon of the oxyd of rpercury, held in folution by the prufTic acid, when iron filings and fulphuric acid are intro- duced. XXX PREFACE. water during the reduftlon of metals, yet I confider her experiments very in- terefling, and well worthy the attention of chemical philofophers. It appears from thofe ingenious experiments, that the different metallic falts, that is, all the metallic oxyds faturated with acids, depofited into the interftices of filk in a ftate of folution in water, were re- duced by hydrogen gas in the ordinary temperature of the atmofphere. The hydrogen of the gas,” fays Ihe, unites to the oxygen of the wa- ‘‘ ter, while the hydrogen of the latter unites in its nafcent ftate to the oxy- “ gen of the metal, reduces it, and ‘‘ forms water.” She alfo fuppofes, when charcoal is ufed, even in the high temperatures, that water is de- compofed, its oxygen uniting to the , carbon, PREFACE. XXXI carbon, while its hydrogen unites to ' the oxygen of the metal and reduces it. I would obferve, that the pure oxyds of metals, (thofe of the noble metals excepted) free from acids, or acid bafes, and depofited in filk, linen, or calico, and moiftened with water, will not be reduced by hydrogen in a common temperature, and fome of them not completely fo in any degree of heat ; hence it follows, that the acid bafis it- felf a£ts a part here, which Mrs. Ful- hame was not aware of; befides, were hydrogen capable of reducing all the metals, its affinity to oxygen mull; be fuperior to any of them, which a va- , riety of well attefted fa 61 :s will refute. And again, if hydrogen were the re- ducer of all metallic oxyds, the differ- ent metals would not only precipitate each XXXll PREFACE. tach Other indifcriminately without any order or nlarked affinity, froiri their folution in acids, but iron would precipitate iron in its metallic ftate* copper would precipitate copper^ and fp with tin and zhic and all other metals. It isj perhaps needlefs to enter more largely into this fubjeft, therefore I will drop it here. I now beg leave to affiire Mrs. F. before we part, that I read her book with great pleafure, and heartily wifli her laudable example may be followed by the reft of her fex ; particularly by thofe who pofTefs talents and means for making chemical experiments. ESSAY ESSAY O N BLEACHING. SECTION I, On Flax. Ripe Flax when pulled out of the ground, is compofed of four diftinft fubftances, .viz. a thin cortex, a green fap, the fibrous or flaxy part and the ligneous matter. The fap or fucculent part is again compofed of an extraftive matter and water, to feparate thefe different fub- ftances'from the flaxy part, it muft firfl be fubmitted to the following B procefs. 2 ON bleaching. procefs. As foon as pulled it is to be fteeped in foft water until the putre- faflive fermentation takes place. This degree of fermentation com- mences with the fucculent part as being more fufceptible of decompo- fition than the reft, for the fermen- tation of animal or vegetable mat- ter is a decompofition of their confti- tuent parts. Were the flax to be continued long in this ftate, the whole fubftance of it would be decompofed or deftro3^ed upon the fame principle that malt is injured by too long fteeping, or that wort lofes its fu bftance by too long a fermentation It muft therefore be taken out of the water while as yet green, and before the whole of its fap is feparated ; but by fpreading it thin upon the ground, and expofing it to ON BLEACHING. J the air, the remainder (being already on the wing of decompofition) is foon carried off or bleached out by the agency of the oxygenous part of the atmofphere. Hard waters, which generally con- tain but a fmall portion of felenite (fulphat of lime) fometimes common fait and muriate of lime, injures the flax, for it foon rots when fteeped in fuch water. This circumftance feems difficult of folution. — We know very well that thefe faline fubftances are ftrong feptics in fmall quantities, but particularly the fulphat of lime which poflefles this property in a higher de- gree than any other faline body, as obferved by Madame D. Arconville^ who, * The wife of a prefident of Parliament at Bourdeaux^ ' ' , ' 4 ON BLEACHING. who, it feems, has made a variety of experiments on the feptic powers of different faline fubftances. I will alfo enumerate by way of analogy, the following ftriking fa6fs, viz. that a fmall quantity of common fait will promote .the putrefaftion of flefh or fifli, while a larger quantity will preferve them — that a fmall quantity of fait taken with our ali- ment will promote digeftion, while an over dofe will produce the contrary effeft — that a fmall portion of fait mixed with vegetable com pofts, will help to fertilife, although a large quantity will render the foil fterile — and laftly, that fea water which con- tains fait but fpaiingly, will produce fimilar effedl, with hard waters, upon dead ON BLEACHING. 5 dead animal and vegetable matter, but in *a more eminent degree. From thefe data one is led to be- lieve, that hard waters aft too power- fully on the flax, by extending the putrefaftive procefs or decompofition to the fibrous, as well as the fucculent part, pretty much about thefafne time. But to return, the flax when in a fit ftate to be taken off the ground, is of a greyifh white colour, very flexible and tenacious, and wholly free from the extra ft ive matter or fap. Nothing, now remains but the wood and flax. The wood is an hollow little tube covered over very compa6tly with the flax ^ to feparate the wood it muft be kiln-dryed, in order to render it frangible or brittle, but care muft be taken not to apply too much heat for fear of injuring the flax. It is next to be 6 ON BLEACHING. be beat or broke, by which means the flax is not only divided into fmall fibres, but moft of the wood is fepa- rated, and the part which adheres, is reduced to fmall fragments. To fepa- rate thefe again, the flax is to be fcutched in fmall parcels at a time, either by manual ' labour or mills con- trived for the purpofe. Hackling is the laft procefs, which is nothing more than drawing, or if I may be allowed theexprefllon, comb- ing the flax in fmall parcels at a time, through a pile or group of polifhed and Iharp iron fpikes placed firmly in wood thro’ an iron plate. The fpikes are placed pretty clofe together ; the firft hackle (for different hackles miift be ufed) is coarfe, the fecond finer, and the third finer again. The ON BLEACHING. 7 The procefs of hackling anfwers a double or triple purpofe ; firft, it di- vides the fibres of the flax, as much as this can be effefted by mechanical means i ad, it feparates the minute fragments of wood which efcaped the procefs of fcutching; and laflly, it feparates the fhort coarfe flax, com- monly called tow. Spinning and weaving are too well known to need defcription, and alfo the preparation which the yarn re- quires previous to its being fet in the loom. SECTION 8 ON BLEACHING. SECTION II. . On bleaching in the old method^ with ge^ 7ieral obfervations on the alkalies. The linen as it comes from the loom is charged with what is called the weaver’s dreffing, which is a pafte of flour boiled in water, and as this is bruflied into the yarn of the warp, before it is wove, it is fomewhat diffi- cult to feparate it when dry. To difcharge this paffe, the linen muff: be fteeped in water for about forty eight hours, when this extraneous fubftance undergoes a kind of fermentation which' does not extend to the fub- ilance of the linen itfelf, upon the fame principle that the green fap is difengaged from the flax without in-" jury to its texture. When ON BLEACHING. g ’When the linen is well walhed after this laftprocefsj it contains nothing that water can feparate^ it is of a greyifli white colour, although the fibres of which it is compofed, when divefted of every adventitious fubftance, are natu- rally very white. • The matter which thus colours the linen, is of a refinous nature, infoluble in water, and from its intimate union or diffemination through the very fibres - of the flax is difficult of feparation, even by thofe fubftances which have a folvent power over it. To difengageit however, in as cheap and expeditious a manner as poflible, without injuring the texture of the fa- brick, is the foie objed: of the procefs of bleaching. Pot-afli c 10 ON BLEACHING. Pot~afh is thefirft menftruum which fhould beufedin bleaching; but perhaps it may not beamifs to makefome obfer- vations on its nature and general pro- perties, before we apply it in this way. All vegetable fubftances, from the fmalleft weed up to the oak, afford more or lefs aflies when burned in open air; which afhes contain different kinds of earths, neutral falts, and a fmall portion of pot-afh or alkali. A given quantity of weeds yields more pot-afh than woods^ as Mr. Kir- wan has obferved in his excellent paper on alkalies, in the tranfaftions of the Royal Irifh Academy for 1789.. I underftand the Irifh farmers burn their weeds (being in every other refpecS ufelefs) every year, in order to obtain the alkali ; hence it is needlefs to fay any ON BLEACHING. II any thing upon this head, only to ob- ferve, that pot-alh is the fame in what- ever climate, or from whatever vege- table it is obtained. The learned Dr. Watfon, formerly profeffor of chemiftry at theUniverfity of Cambridge, and now bifhop of Lan- daff, has jfhewn that 1300 tons of dry oak yield 15 tons of afhes ; and that thefe afhes again afford only one ton of pot-afh 5 hence it appears that we cannot expeft any great fupply in this country, but that we muft ever look up to foreign nations, which abound with forefls for this ufeful article. T o feparate the pot-afh or alkali from the other ingredients in the afhes, they mufi: be put into ten or twelve times their weight of boiling water, .or ac- . cording to chemical language, . in 12 ON BLEACHING. . in water. By this means the pot-afh, (from its great folubility) togetherwith the other fallne fubftances, arediflblved, while the earthy part, being nearly in- foluble, is left behind. The folution or lixivium is to be drawn off clear from the dregs, and evaporated to drynefs in iron pots, and hence it is called pot-afh. Pot-afh is far from being a pure fait j it contains from 20 to 25 per cent, of impurities, confifting principally of fulphat of pot»afh%nd carbonic matter. To free the pot-afh from carbon •f' or any otherinflarrimable matteritmay contain, it is expofed to the joint adion of * Sulphat of pot-afh is a neutral fait, compo- fed of pure pot-afh and oil of vitriol, now called fulphuric acid. + The term carbon is derived from caibo, the latin word for charcoal. ON BLEACHING. 13 of air, and a moderate red heat, upon the bed of a reverberating furnace.^ Thus, the inflammable matter being burned out, the pot-afli, from being of a darkifli grey colour, acquires a pearly white; it is hence called pearl-alh. Pearl-afli contains from loto 12 per cent, of impurities, moftly fulphat of pot-afh, and fometimes a fmall portion of muriate^ of pot-afh. Thefe falts muft have been yielded by the wood, and diflblved by the large quantity of water neceffary to feparate the pot-afh from the afhes. I more than once obtained near 20 per cent, of fulphat of pot-afh from the pearl-afh imported here ; this great portion of fulphat of pot-afh could have never I * Muriate of pot-afli, a neutral fait, confiftin^ of marine acid and pure pot-afh. ON BLEACHING. 14 ‘ never been a natural produft, but muffc have been an artificial adulteration j and indeed, circumftances have con- vinced me that it miift be fo. During a mineralogical excurfion through England in the fummer and autumn of the year 178 5, the different manufactures which fell in my way, were not paffed over. Upon enquiring of the diflillers of aquafortis ( nitrous acid) how they difpofed of the large refiduum left in the ftill (when the acid was carried over) which is fulphat of pot-afn, and which is of little or no ufe in the arts, they informed me it was bought up by the Irifh merchants. Sulphat of pot-af]i, when ground down, cannot readily be diftinguiflied as to its external appearance from pearl- afh, and being fo much cheaper than the . ON BLEACHING. 1 5 the latter, is well calculated for the above fraudulent purpofe. By no means do I intimate that this is a common praftic.e, as from expe- rience I know the contrary. However, to pafs it over in filence would be unpardonable, when it is confidered that the bleacher is at the ex- pence of an article of no ufe whatever in bleaching, and that, by the adulte- ' ration, the proportion bell: known by experience to anfwer his purpofe is va- ried; by which means his procefs, al- though not altogether fruftrated, muft be materially retarded. Sulphat of pot-afh is only foluble in about fixteen times its weight of water, in the temperature of 6o^, while realpbt-afh is foluble in its own weight of water, in the fame temperature ; hence ^6 .ON BLEACHING. hence they are eafily feparated in the following fimple manner,, viz. three pounds of pearl-alh and two quarts of water fhould boil together for a few minutes, then be removed from the fire and fuffered to ftand for twenty-four hours, when the clearJiquor is to be decanted off. Half a pint more of cold water is to be poured upon the dregs, and this again drawn off when clear : The infoliible fait is afterwards to be well dried and weighed, w^hich, being a foreign fait, will give pretty nearly the quantity of impurities in the pot-afli. I would recommend the above mode of analyfis to the bleachers before they purchafe or ufe their pot-afh. Common pot-afh when freed from earthy, inflammable, and foreign faline matter is ftill impure, being chemical- ON BLEACHING. ^7 ly united to carbonic acid gas (fixable air*.) This combination does not al- together deprive it of its detergent property. To obtain pot-afti perfeftly pure, if muft be deprived of the carbonic acid : This is effefted by quick lime, which has greater affinity to the acid than the pot-afh has. The lime is to be flaked and fifted, and thepot-aflidiffolved in water; then mixed and boiled'f-, and laflly, (trained or filtered, or fuffered to fubfide. The clear liquor is a folution of pure pot-afh, ' and fhould not contain a particle of D lime, * Called carbonic acid, as the matter of char- coal is one of its conftituent principles. , + Upon a large fcale there is no neceflity for boiling the mixture, but to fuffer it to ftand for a few days before the pot-afh is drawn oflF. The mixture fhould be ftirred pretty often. ON BLEACHING. i8 lime. This is what is commonly called foap-lyej the alkali requiring this treatment before it can make Ibap. Pure pot-afh, according to our pre- fent knowledge of chemiftry, is a lim- ple elementary fubftance, and in this ftate, being uncombined or uninflu- enced by any body whatfoever, its at- traftion is much encreafed for thofe fubftances to which it has affinity i fuch as fuet, oil, refms, gums, and in fhort, all animal and vegetable in- flammable matter. Its attraction to animal matter is fuch, that it inflant- ' ly corrodes or diflblves the Ikin and flefh of animals when brought into, contaft with them.; hence it is called catcftic lye or caujiic alkali while the carbonated pot-afh from being much weaker, is termed mild alkali. It ON BLEACHING. 19 It IS upon the foregoing principle that foaps are made, which confitt of animal or vegetable fats and pure al- kaline lye. Soaps, although compofed of lye and oils, or greafe, or fats, are ftill poffefled of a detergent pro- perty, that is to fay, they are capable . of combining with more greafe or in- flammable matter, and diflblving a large portion of it by the afliftance of heat. This comprehends the whole the- ory of wafliing or cleanfing of linen* Mild pot-^ap (the lye united to car- bonic acid gas) is a more powerful de- tergent than foap j fp much fo, that its frequent ufe in the wafhing'of linen would deftroy its texture, and wear it down too foon. Cauftic lye or pure pot-alh has a fimilar effefl with the mild, but in a higher 20 ON BLEACHING. higher extreme; I would however fup-^ pofe, that it might, when reduced, or fufficiently diluted with water, be ad^ vantageoufly fubftituted for foap in the cleanfing of coarfe linens, particu- larly in hofpitals. ' Cauftic, or pure pot-afh, fhould ever be ufed by the bleachers, as having a greater folvent power over the colour- ing matter of the linen than the mild; befides, a given quantity of the for- mer* will go farther than the farne quantity of the latter. The immediate application of lime to the linen, either by itfelf, or mixed with pot-afh, fhould be avoided; for al- though it has the property of bleach- ing, it deflroys the texture of the cloth. 1 have tried it in Various ways and proportions, and don’t hefitate to for- bid the ufe of it. The ON BLEACHING. 2 \ The cauftic lye, it is true, unlefs properly diluted, is capable of injuring the cloth; and fo is fblphuric acid (oil of vitriol) which is knov/n to be ufed with great fafety as a fouring. Marine plants afford by incineration afubftance poffefling the fame property with pot-afh, particularly fo far as relates to bleaching and foap-making. This fubftance, being perhaps originally ob- tained from a marine plant called kali, hence derived the name alkali, which is now the common name for both fub- ftances; for hitherto, only two fixed alkalies, and one volatile hav« been difcovered, and perhaps in nature there are no more. The latter alkali Jis the produdlof the animal kingdom, and being remarkably volatile, is ne- yer ufed in bleaching. 22 ^ ON BLEACHING. The two fixed alkaMes are diftln- guiflied from each other by the names vegetable alkali aiid mineral alkali^ the latter being found in.great abundance in the mineral kingdom, united to mu- riatic acid in the ftate of common fait. It is found native, united only to car- bonic acid gas, in hot climates, parti- cularly in Egypt, and many other parts of the Eaft, in a ftate of efflorefcenee upon the furface of the ground. It is alfo found native in cold countries, par- ticularly in Ruffia. Moft of what is ufed in England and Ireland is extract- ed from the allies of marine plants. Thofe which come from Alicant, and many countries bordering on the Me- diterranean, are the richeft. The plants called foza, faiicornia, gazulla, and barilha, afford moft alkali^ particu- larly ON BLEACHING. 23 lariy the former and the latter; hence the aflies, which are a greyifh or bluifh black fufed mafs, go by the name of barilha ; and the alkaline fait, when feparated from foreign impurities, is called foda. The marine plants of our own fhores afford foda in very fmall proportions. Their allies, which in external appear- ance cannot be readily diftinguifhed from barilha, are called kelp. The lat- t ter contains more foreign falts than the former, particularly fea fait. Thefe two fubftances are often mixed with each other, a fpecies of impolition not eafily detefted but by analyfis. This is effeded by boiling the aflies, firft reduced to powder, in thrice their weight of water, and then filtering the liquor. The refiduum on the filter is again to be boiled with half the quan- - . tlty- 24 ON BLEACHING/ tity of water, and filtered or ftrained. The clear liquors are to be mixed while hot, and fet by to cryftallize. Moft of thefodawhen extradted from . either barilha or kelp, is cauftic, and will not cryftallize in that ftate; therefore the folution muft ftand five or fix days expofed to the air, in order to imbibe carbonic acid gas from the furrounding atmofphere, which contains more or lefs of this gas in every fituation. If the barilha be not good, it will not af- ford any cryftals in the above quantity of water; in this cafe it muft be eva- porated down one- third, and fet by again*. When cryflallized, themother- water * I frequently failed in the cryftallization of foda in every degree of ftrength in the liquor, until evaporated down to perfe£f drynefs, and redilTolved again in frefh water, when it readily cryflallized; but whenever this happened, th^ barilha was not of the bell kind. ON BLEACHINGi 25 water is to be decanted off, and eva- porated down one half; daring this fecond evaporation, if it contain much fea-falt, that fait will make its appear- ance, and cryftallize in the hot liquor; being no more foluble in hot water than in cold; this is feparated by ftraining the folution while hot. The liquor on cooling will depofit a fecond crop of cryftals of foda, at the fame time that the common fait will remain in folution. This procefs muff be repeated, every fubfequent mother liquor being partly evaporated, until as much as poffible of the foda is obtained'^ . This kind of treatment is fufficient for the bleacher's purpofe, the quantity of alkali being his only object. For a E ^ . more * Good barilha contains from fifteen to fixteen per cent, of cryftaliized foda more than kelp. 26 ON BLEACHING, more accurate analyfis of the different materials contained in the barilha, fee Kirwan on alkaline fiibftances. Irijh tranfaBions for 1789. ,pThe bleachers, when they ufe foda, avoid the expence and trouble of ex- trafting it from the afhes ^ they charge the barilha in powder into a coarfe linen bag, and boil it with the cloth, thus the alkaline part is extradted by the water, while the infoluble dregs remain behind in the bag, which ftiould be of thick canvas, and being already pretty nearly in a cauftic ftate, the media- tion of quick-lime is unneceffary. From the foregoing outlines of the general properties of alkalies, particu- larly thofe of pot-afh, which is the alkali moft frequently ufed, it is eafy to conceive what part it adls in the bleaching of linen. The ON BLEACHING. V The pot-afli or alkali, from its fol- vent power over the colouring matter, diffoives and feparates the part imme- diately expofed to its aftion ^ that is to fay, the part of it which refts fuperfici- ally upon the fibres of the flax or thread ; I fay fuperficially, for it requires ten or twelve repeated boilings at leaft, with the alternate agency of the atmofphere, to feparate the whole of the refin. It might be afked, why fuch an ac^ tive folvent as pot-afh fhould not carry away the entire of the refin at once, or at leaft as much as it alone could in any way feparate. — This requires an explanation. What appears to us to be a Angle ultimate fibre of flax in grey linen, is com^.ofed of a bundle of minute fila- ments, clofely cemented or agglutinat- ed 28 ON BLEACHING. ed .together by the refmous matter ; therefore the pot-alh firft ufed only afts upon the refin of the external cociting of filaments, by which means they are loofened or feparated, and ex- pofed to the further aftion of the air. The fecond boiling in pot-afh opens a fecond layer, and thus fucceffively layer after layer until the entire is di- vided or opened to the centre. Were the folution of pot-afh fufH- ciently ftrong to force its way at once to the centre, it would aft upon the filaments themfelves and deflroy the texture of the cloth. Each filament, after the procefs of pot afh, retains an impregnation of co- louring matter, fo intimately united as to refift the further aft ion of it. This can only be removed by the flow and gradual influence of the atmofphere. Bu^ ON BLEACHING. 29 But upon what principle does at- mofpheric air aft ? To underftand this clearly, a previous knowledge of the nature and properties of it, is abfolutely neceffary. The atmofphere in which we are immerfed, and which furrounds this globe we inhabit, preffes upon every fquare inch of its furface with about the weight of fourteen pounds. It is ' compofed of two fluids or airs, me- chanically mixed or diffufed through each other (to compare denfer bodies to rarer) like fpirits and water, or fu- gar and water. One hundred parts of this air contain only twenty-feven, ca- pable of fupporting combuftion or ani- mal life ; hence called vital air ; the other feventy- three parts are the re- yerfe of it in both thefe refpefts, and are 3^ • ON BLEACHING. are called azotic gas*. By burning a body in the air, or by the refpiration of animals, the vital part (now called oxygen gas-f-) is abforbed and fepara- ted.from the azotic gas which is left behind, and which extinguifhes bo- dies in combuftion, and kills animals. Thus by combuftion and refpiration, an analyfis of the atmofphere is ef- fected. Moft inflammable bodies refift the attraction of the oxygenous part of the atmofphere in a' common, or even in a much higher temperature. This pro- ceeds * Azot is derived from the Greek privative, particle a and vUa from its quality of killing animals in the aft of breathing it. + Called oxygen gas, as being one of the conhituent principles of all acids, and it is fupr pofed that an acid cannot exHl without its pre- fftice. It is derived from the Greek o^vsy aadu?n^ and gignor. Hence a compound word fignii'ying the acid-getting principle. ON BLEACHING. 3 I ceeds from two caufes, which co- operate with each other : The one, from the attra6liqn of caloric^ (the matter of heat) to*the gravitating or folid matter of oxygen gas. The other proceeds from the attraftion of aggre- gation, or that' influence which the moft minute or ultimate particles of all folid bodies exert upon -each other In a higher or lefs degree. Thus, for example, Carbon or fulphur, although both highly inflammable, will not burn in contadl with air, until this in- fluence is in a great meafure done away ; This is effe6ted by an high temperature, or in other words, by caloric, whkh pe- netrates between their particles. B y this means they are removed beyond each others * Caloric, the matter of heat, derived, from, - ^Alor the latin for heat. 32 ON BLEACHING. I Others mutual influence, and confe- quently are left at liberty to direft the whole of their attraftion towards the oxygenous part of the atmofphere. ^ The fire or caloric evolved during the aft of combuftion, comes from the air; the burning body, from fupe- rior affinity to its oxygen, only liber- ating the caloric from its chemical union with it : for caloric chemically united, is not felt, nor does it aft as caloric ; — juft as cryftallized falts which contain half their weight of water, will not wet or feel moift to the hand, or as fulphuric or nitrous acid, when united to an alkali, will not corrode. From the above ftatement of the properties of oxygen gas and pot-afh, their modus operandi is very obvious. The pot-afli diflblves in each boiling, a certain on BLEACHING. 33 a certain quantity of the colouring matter, and partly divides the fila- ments of each fibre of the flax ; the oxygen gas, in its turn, unites to the . portion {till adhering to thofe fila- ments that eluded the a6lion of pot- afli, with which it forms carbonic acid gas*. The carbonic acid gas, from its volatility, flies'off and mixes with the atmofphefe. Thus alternately, the one diflblving and the other burning out (for bleach- ing is flow combuflion) the linen is whitened. * Water is alfo formed in proportion to the c^iiantity of hydrogen the refm contains. ' F SECTION ON BLEACHING, 34 - Section hi.- On hie aching, ’with the oxygenated muriatic actd, and on the methods of preparing it. As atmofphcric air is the molt tardy menftruum in bleaching, requiring as many days and nights upon the green, as hours in pot-afli, it has ever been confidered a great dbjeft to accelerate its combination with the colouring matter. To promote the fpeedy adtion of at- mofpheric air, or rather the oxygenous part of it, in its ordinary elaftic ftate, is well known to be impoffible. ■The prefent advanced ftate of chemif- try, however, has enabled us indiredlly to ON BLEACHING. 35 to obviate thofe obftacles. Firft, by condenfing or combining the oxygen of the atmofphere, with fubftances to \vhich it has great affinity ; adly, by transferring it again from thofe fub- ftances, to others to which it has lefs affinity, but fufficient attraftion to re- tain it in a concentrated ftate 5 and laftly, by fteeping the linen in this laft compound, which readily imparts its oxygen to the colouring matter. In order to be more explicit, I will obferve, that mofl: metallic bodies have ftrong attraction to oxygen gas ; for ' inftance, lead when melted, or pene- trated by a fufficiency of the matter of heat, fo.as to remove its aggregate in- fluence, will drink in,"if I may be al- lowed the expreffion, one twelfth of its own weight of oxygen. , - Ey ON BLEACHING. By this union, the lead lofes its me- tallic brilliancy and cohefion, and af- fumes a loofe earthy appearance and reddifh colour, hence called red-lead, W hen fulphiiric acid (^oil of vitriol) is poured upon red-lead, part of its oxygen is expelled in an aeriform date, that is, combined with caloric. All metals thus united to oxygen, are called oxyds, diftinguifhed from each other by the name of their re- jfpedlive metals; as for inftancq, oxyd' of lead, of iron, of tin, of copper, &c. Hence it appears, that metals, being in themfelves fixed bodies, are the fitted: fubftances to withdraw oxygen gas from the atmofphere, and to fix and concentrate it. Some metals, but particularly a black femi -metallic fubffance called manganefejj I ON BLEACHING. 37 manganefe, are found in the ftate of oxyds in the bowels of the earth. Manganefe, from its great affinity to " oxygen, is never found in any other ftate. Manganefe, as well as the reft of the oxyds, will not impart its oxygen to the colouring matter of the linen even in a boiling heat, when diffufed in water, or in any temperature fhort of that which would deftroy the tex- ture of the cloth. The oxygen therefore, thus col- lefted, and attached to the metal muft, as obferved above, be transferred to another fubftance which retains it with lefs force, and confequently imparts it more freely to the furface of the linen. To effedl this, the following are the materials and proportion ufed, viz. the oxyd of manganefe lixty pounds, com- - " ‘ mon ■ . \ ON BLEACHING. mon fait fixty pounds, and fulphuric acid fifty pounds* diluted with its own bulk of water-p. The manganefe is to be finely ground and well mixed with the fait, and charged into a leaden Hill, fufficiently capacious to hold forty gallons of wa- ter, in order to allow fpace for the fwelling of the ingredients during their chemical a£lion upon each other, v/hich, at the commencement of the procefs, is very confiderable. The ftill ftiould be rather of a coni- cal form, that is, fomewhat progref- fively widening from the bottom to nearly * Called fulphuric acid, fulphur being the bafis, and oxygen the other principle. i 'Forty-five pounds of good fulphuric acid, of fuch fpecific gravity that a pint will weigh twenty-nine ounces, will be found fulfil cient, when inftead of plain wrater, the acidulous liquor in the middle receiver is added, which, will hereafter be deferibed. ON BLEACHING. 3^ nearly the upper part. The mouth or aperture of this apparatus is to be fit- ted with a flat or conical leaden cover, ■ which is to refl: in a groove, and the junftures are to be luted with well tempered blue clay. An iron rod or upright, covered over with lead, is to be fixed in the centre of the cover as tight as poffible, ' without impeding a rotatory motion. — It fhould reach to the bottom of the flill with prongs or. wings to that part which enters the charge, in order, oc- cafionally, to mix the materials, and to bring all their parts to a6l upon each other. A leaden funnel fhould alfo be in- ferted, air tight, into another part of the cover, with a long flem which fhould curve upright a few inches un- derneath it. This will prevent the efcape 46 ON BLEACHINGi efcape of the elaftic fluids, dlferigaged, during the charging of the fulphuric acid upon the materials, which would be highly injurious to the workmen. It is, I fhould fuppofe, unneteflary to explain the principle upon which the curved funnel a£ts, fuffice it then to fay, that two columns of fulphu- ric acid of equal weight, the one in the curved part, and the other in the perpendicular, reft in the flem of the funnel, which balance each other, and which, by their gravity, prefs againfl: the expanfive force of the internal elaf- tic fluid. — Were the ftem of the fun- nel ftraight, the elaflic fluids would fometimes make their efcape, even .againfl the current of the fulphuric acid pafling through it. A leaden ON BLEACHING. 4I . A leaden tube, three inches dlame- , ter in the bore, and of convenient length, fhould communicate from the cover to a leaden receiver large enough to hold about eight gallons. This is to contain water only, and fhould be two-thirds filled with it; ano- ther tube of the fame diameter with the former fhould pafs from this receiver, above the level of the water, to the upper part of a veflel, or cafk fuffi- ciently capacious to hold eight hundred gallons of water, and eighty pounds of well-flated and fifted quick-lime. As the lime, from its fuperior fpecific gravity to water, would fink in it and- fall to the. bottom of the receiver, it is neceflary to ufe fome means of keeping it fufpended. For this purpofe, an up- right agitator, fuch as was recommend- G ed 42. ON BLEACHING. edfor the leaden fHIl, fliould be adopted here; but the latter is to be of wood. By this contrivance a rotatory motion may be communicated to the liquor at pleafure. T wo or three boards or wings fliould alfo be fixed to the fides of the calk at right angles; the liquor, by -dafhing againfl: thofe, will acquire ad- ditional motion. Thus a continual fur- face of frefh lime, liquor will be pre- fented during the procefs, to the oxy- genated muriatic acid gas, which will much facilitate its condenfation. This fliort defcription will give a fufficient idea of the apparatus, and of the expence attending it. Thofe who ufe it, I underftand, find it very conve- nient, but doubtlefs praflice will im- prove it. The apparatus itfelf may be feen at work at the bleach-green of Charles ON BLEACHING. 43 Charles Duffin, at Dungannon*. A .Mr. Tennant who works for him, and who, it feems, is very expert at the procefs, may be employed by the diffe- rent bleachers, until they get into the method of managing it themfelves. As the lead would be liable to melt, if expofed to a naked fire, in confe- quenceof the folid materials refting up- on the bottom of it, and as the heat of boiling water- is fufficient to work the charge, the ftill fhould be placed in a copper or iron boiler, large enough to admit a fufficient quantity of water to furround it. ' ' The apparatus being thus difpofed, it remains now to attend to the theory , and management of the procefs. ' . The * Since the above was written, I have been informed, that no lefs than thirty fuch apparatus ajre now ufed in the north of Ireland. 44 ON BLEACHING. The oxyd of the manganefe and fait being charged into the ftill, the cover luted on, and the whole of the appa- ratus being connected together, the ful-. phuric acid is to be gradually poured on by means of the curved funnel: The Sulphuric acid, the inftant it comes in contaft with the other materials, adts partly.upon the fait, while another por- tion of it unites to the manganefe. Manganefe is an oxyd, a metal fatu- rated with oxygen gas : Common fait is compofed of muriatic acid gas and an / alkaline fait called foda, the fame which barilha afibrds : Manganefe has a great- er affinity to fulphuric acid than it has. to the oxygen^, and' the foda of the fait greater affinity to fulphuric acid than to the muriatic acid gas ^ hence it ne- ceffarily * The quantity of oxygen neceffary to me- tallic folution is excepted here. ON BLEACHING. 45 ceflarily follows, .that thefe two gafes, (orratherthelr gravitating matter,) muft be liberated from their former union in immediate contaft with each other; and, although they have but a weak affinity to one another, they unite in their nafcent ftate, that is to fay, before ' they individually unite to caloric, and feparately affiime the gaffeous ftate; for oxygen gas, and muriatic acid gas, already formed, will not unite when mixed, in confequence principally of the diftance at which their refpeftive atmofpheres of caloric keep their gra- vitating particles ^under^. The * Common muriajtic acid, - that is, water fa- tiirated with muriatic acid gas, poured upon the manganefe, will afford the oxygenated muriatic gas ; but as the acid muft firft be difengaged from the fait, by means of fulphuric acid, and diftilled, this would be an expenfive method. 46 GN BLEACHING. The compound refulthig from thele two gafes, ftill retains the property of affuming the gaifeous ftate, and is the oxygenated muriatic gas. Heat fliould not be applied until the firft a6lion of the fulphuric acid upon the dry materials, (which is rather com fiderable) nearly fubfides, otherwife the oxygenated muriatic gas will be genera- ted fafter than it can be condenfed,which would endanger a rupture of the veffels. At the commencement of the procefs, a portion of the muriatic acid gas ef~ capes uncombined with oxygen gas, which were it condenfed in the oxy-^ genated liquor, would be rather inju^ rious to itj but common muriatic gas, being more condenfable in water than the oxymui iatic gas, is arrefted and con- denfed in the middle or leaden receiver^ — fuch is the principal ufe of this part * of ON BLEACHING. 47 of the apparatus. The pure oxygen gas pafles into the wooden receiver, where it is abforbed by the lime, and the compound, being a foluble fubftance, is difiblved by the water in the condenfer. This liquor is the oxygenated muri- ate of lime, and may, foon after the procefs is over, be drawn off clear from the infoluble dregs, which 'in a ftiort time fubfide to the bottom. In this ftate, it is of fufficient ftrength to bear thrice its bulk of water for the purpofe of bleaching. . The refiduum in the ftill confifts of fulphat of manganefe, fulphat of foda, a fmall portion' of muriate of manga- nefe, and fome oxyd of manganefe which efcaped the aflion of the acids. The latter fubftance being infoluble, the different falts may be feparated from it by ON BLEACHING. 48- by means of hot water. This refiduary manganefe, when well walhed and dryed, may be ufed over again in a frefh charge. The oxygenated muriatic acid gas was firfl: difcovered by the immortal ScHEELE, a celebrated Swedilh chemift. The application of it in the art of bleaching, was referved for Berthol- . LET, a famous French chemift, who firft recommended it condenfed in plain wa- ter. This method, however well it may anfwer in fmall experiments, was after- wards found inconvenient in the large way; for firft, the water condenfes the gas fo very fparingly , that the apparatus ufed muft neceflarily be upon too large and expenfive a fcale. sdly. Water con- denfes the gas fo flowly, the procefs muft be tedious, for the charge cannot be worked fafter than the gas is abforb- ed; ON BLEACHING. 49 td j and laftly, water retains the gas fo very weakly, that it is continually fly- ing off during the application of the liquor, and is not only loft, but highly injurious to the workmen. Hence this method had been after- wards fuperfeded by a folution of pure pot-afh, which was found to obviate the above inconveniencies, by more effeflually condenfing and fixing the gas. Although the oxygenated muriate of pot-afli has been ufed with great advantage by the paper-makers, it does ' not appear to have made any great progrefs in our bleach-greens. What fuccefs the oxygenated muriate of lime may be attended with, I will not at prefent take upon me to fay ; this can only be afcertained by the progrefs it will make amongft the moft H enlightened 50 ON BLEACHING. enlightened of the bleachers, who are ever ready to adopt every means likely I to fave labour and expence. I muft, however, obferve, froma feries of com- parative experiments which I made upon it and the oxygenated pot-afh, /by order of the Linen Board, that the former, as being cheaper, and lefs liable to injure the texture of the cloth, has decidedly the preference. By the experiments I made, it ap- peared, that fix boilings in pot-afh and alternate fteepings in the oxygenated lime-liquor, bleached the linen well 5 but it was liable to turn yellowifh by boiling in foap, or repeated waftiings : Hence it was found neceflary to bleach the linen partly in the common way firft. According ON BLEACHING. 51 According to the information I have received from Mr. Duffin, the follow- ing is the method praftifed by thofe bleachers who ufe the oxymuriate of lime, viz. ift, four boilings in pot-afli, and four weeks expofure to the air, zdly, two immerfions in the oxyge- nated lime, with an alternate boil in pot-afh, and a "week’s grafs between each boiling or immerfion ; after this treatment the linen is fit for the boards and fours. , • During the fummer months two boilings in pot-afh, and a fortnight’s expofure to the air is fufficient to pre- pare the linen for the oxygenated li- quor; after this, three boilings in the . alkali, and alternate fteeps in the oxy- genated muriate of lime will finifh it. From ON BLEACHING. 52 From the foregoing view of the theory and pradice of bleaching, it is evident, that whether the linen be bleached in the ufual way by the tardy procefs of expofing the cloth to the a6lion of the oxygen gas of the atmof- phere, * or by the more expeditious method of ufmg the oxygenated li- quor as an auxiliary, the ufe of pot- afii, or a fuhjlitute for it, is indifpen- fably neceffary. How far I have been fuccefsful as to fuch a fubftitute, the following feftion will evince. SECTION ON BLEACHING. 53 SECTION IV. On fulphuret of limey as a fubfitute for pot-ajh. Since I had the honour of being ap- pointed chemift to the Linen Board, which is now more than three years, I have allotted a confiderable portion of my time and attention to the in- veftigation of the principles of that fcience, applicable to the art in which I am thus more particularly interefted. It appeared, that until pot-afh could be difpenfed with, we muft for ever remain in the power of foreign na- tions as to our ftaple commodity: Ob- ferving alfo, that all the late improve- ments in bleaching were exclufively confined to the one object — that of im- parting 54 ON BLEACHING. parting oxygen to the cloth, in a fafe and expeditious manner, but that there had been no effort made to fuperfede the neceffity of pot-afh, by far the moit expenfive and uncertain article employed by the bleacher, and for which he is entirely dependent upon foreign markets ; I directed my atten- tion chiefly to difcover a fubflitute for pot-afh ; which, provided it Ihould be of I rifhproduftion, though it might be equally expenfive, I conceived would be of the utmoft national importance. Impreffed wdth thefe ideas, I under- took a feries of experiments with that view, To enumerate the many difappoint- ments and failures I experienced dur- ing my invefligation, would be end- lefs, and an unneceflary intrufiqn upon ON BLEACHING. 55 upon my reader. — Knowing, from an important obfervation of Mr. Kirwan, that faline hepars, or the combination of an alkali with fulphur, might, from its detergent properties be advanta- geoufly employed in bleaching, as a fubftitute for mere alkali, by an obvi- ous analogy I was led to expedt a fimilar effedl'from calcareous hepar, or, more properly fpeaking, fulphuret of lime, being a combination of lime and fulphur. In thefe expedlations I was not dif- appointed, but at that time (about three years fince) I contented myfelf (rather through neceffity, for large cities are very unfavourable to experi- fnents on bleaching by expofure to the atmofphere,) with pointing it out to fome of the principal bleachers from the north then in town, earneftly re- ' commending I \ 56 ON BLEACHING. Gommending it to them to give it a fair trial with; and without pot-afh. Since that time, alkaline falts having become progreffively dearer, and in confequence of a late propofal of fub- ftituting lime for pot-afh, in con- denfing the oxymuriated gas, I was inftigated to refume the fubjedl, and make further and more varied trials. The refult of which has been, that the ufeof thefulphuret of lime may bemoft advantageoufly combined with that of the oxymuriated lime, and that thus cloth may be perfedlly whitened with- out the ufe of a particle of alkali. This then alone would feem to give it a decided J3reference over the methods at prefent in ufe, while at the fame* time it pofTeffes peculiar advantages, and is exempt from the principal ob- jedlions to which other fubjiitutes are liable ; ON BLEACHING. • 57 liable ; for ift quicklime and fulphar, the materials of which the calcareous hepar confifts, are both articles of tri- vial expence, efpecially as the latter enters but fparingly into the compofi- tion ; adly, their combination is effeftr ed in the eafieft and moft expeditious manner poffible, and perfeftly level with the capacity of the meaneft work- man ; 3dly, as the manner of its ap- plication is, by fteeping the cloth in it cold, the faving of fuel is a matter of great magnitude ; and laftly, there is no danger to be apprehended in the ufe ' of it, from the unlkilfulnefs or negli- gence of the workman, as it appears to be incapable of injuring the texture of the cloth. The fulphuret of lime is prepared in the manner following Sulphur, or brimftone in fine powder, four pounds, ^ lime well flaked and fifted twenty I ^ pounds; ON BLEACHING. 58 pounds, water fixteen gallons' j thefe are all to be well mixed and boiled for about half an hour in an iron veffcd, ftirring them brilkly from time to tirhe. Soon after ^ the agitation of boiling is over, the folution of the ful- phuret of lime clears, and may be drawn off free from the infoluble matter, which is confiderable, and which refts upon the bottom of the boiler^. The liquor in this ftate, is pretty nearly of the colour of fmall beer, but not quite fo tranfparent. Sixteen gallons of frefli water are af- terwards to be poured upon the infoluble dregs in the boiler, in order to feparate the whole of the fulphuret from them. When * Although lime is one of the conftituent prin- ciples of the fulphuret^ yet being fo intimately united to the fulphur, it has no. longer the pro- perty of lime ; upon the fame principle that fidphuric acid in fulphat of pot-afli^ has. not tl^e property of that acid. ON BLEACHING. 59 When this clears (being prevloufly well agitated) it is alfo to be drawn off and mixed with the firfl: liquor ; to thefe again, thirty three gallons more of wa- V . ter may be added, which will reduce the liquor to a proper ftandard for fteeping the cloth. . Here we have, (an allowance being made for evaporation, and for the quantity retained in the dregs) fixty « gallons of liquor from four pounds of brimftone. Although fulphur by itfelf is not in ’ any fenfible degree foluble in water, and lime but very fparingly fo, water diffolving but about one feven-hun- dredth part of its weight of lime j yet thefulphuret of lime is highly foluble*. * When the above proportion of lime and fulphur is boiled with only twelve gallons of wa- ter, the fulphuret partly cryftallizes upon cool- ing, and when once cryftallized, it is not eafy of folution. , SECTION 6o ON KLEACHING. SECTION y. On bleaching with the fulphuret of lime. When the linen is freed from the weaver’s drefling, in the manner al- ready defcribed, it is to be fteeped in ■the folution of fulphuret of lime (pre- pared as above) for about twelve or eighteen hours, • then taken out and very well walked ; when dry, it is to be fteeped in the oxymuriate of lime for twelve or fourteen hours, and then waftied and dried. This procefs is to be repeated fix times, that is, fix alternate immer- ON BLEACHING. 6i immerfions in each liquor, which I found fufficient to whiten the linen. When I fubmitted the linen to fix , boilings in pot-alh, and to fix immer- fions in the oxygenated liquor, is was not better bleached than the above. The three firft' boilings in pot-alh, it is true, produced a fomewhat better effeft than as many fleeps‘ in the ful- phuret ; but towards the conclufion, that is, when the linen was bleached, the fmalleft difference was not obferv- able as to colour. The linen bleached with the pot-afh was thinner, or more impbverilhed than that treated with fulphuret, and the latter flood the teft of boiling with foap much better than the former, although it did acquire a flight yellowifli tinge, which I fliould fuppofe a week's, or at mofl, a fort- night's grafs, as they term it, would re- move. I con- 62 ON BLEACHING. I contrafted the efFefts of hot and cold fulphuret in various temperatures, and although *the difference appeared in favour of the hot liquor, yet it was fo trifling as not to deferve confidera- tion, or the expenditure of the fmalle-fl: quantity of fuel. When I fteeped the linen in the fill-' phuret firfl, and afterwards boiled it in pot-afh, and then immerfed itpnce in the oxygenared liquor, a better ef- fe6l was produced, than from two previous boilings m pot-afh, or from two 'fteeps in the fulphuret ; fo that the two fubftances feem to co-operate with, each other. Indeed, from what I have feen, two fuccelTive fteeps in frefh fulphuret, pre^ vious to the immerfion in the oxyge-- iiated liquor, feemed to afford very lit- ' . . < tie ON BLEACHING. 63 tie better efFedt than a fingle one, which is not the cafe withjefpedl to pot-afli. It was obfervable, that the cloth was Invariably thicker or more fwelled com- ing out of the fulphuret, than after be- ing boiled in pot-afh, and remained fo when even wafhed and dried. It appears to me, that the fulphuret opens the fibres of the linen more fpeedlly and better than the latter, by foftening and fwelling, rather than by dllTolving, the refinous or colouring matter. This accounts for the bet- ter effeft of pot-afh upon the linen when previoufly fteeped in the ful- phuret, than when iifed by itfelf. Probably thofe bleachers who do not at prefent find it convenient to ufe the oxygenated liquor, but continue to bleach by expofure to air, may derive fome ON BLEACHING. 64 fome advantage. from this, by ufing the fulphuret and pot»aflh conjointly or alternately. Mr. John Duffy, of Ball’s -bridge, (who from his knowledge of chemif- try is very well acquainted with the principles of bleaching) was kind enough to repeat the above experi- ments, and his report to me corref- ponded with.my own obfervations. It is almoft impoffible to afcertain to the. full extent, more efpecially by fmall experiments in- an elaboratory, the many advantages any fubftance not hitherto ufed in bleaching, will af- ford by varying the mode of applica- tion. The experimenter does a great deal by difcovering the efficacy, proving the pradlicability, and afcertaining the fafefl and moft economical niethod of diredlly . ON BLEACHING. ' 65 direftly ufing it, and alfo the beft proportion of it. Before he can ar- rive at any one of thefe, many a round of changes are neceffary ; indeed a greater number than any man who is not ufed to experiments can be av/are of. But I. fhould hope, that the bleacher need not hefitate to ufe it in the ftate in which I prefent it to him, more efpecially as he runs no lifque of injuring the cloth with it. If he can make more of it hereafter, I (hall feel happy upon the occafion ^ no dif- covery was ever brought to perfeclioii at once. How gradually, and yet how pro- I greffively the fteam^ engine, from its firft invention by the Marquis of Worcefter, was brought to its prefent degree of perfection ? Undoubtedly, it was juft fo with refpeCl to alkalies, K the 66 ON BLEACHING. the fubftances now ufed by the bleaeh-i ers, it muft have taken’ a confiderable time after their firft ' application in bleaching, befoje they could be made the moft of. I will now conclude by pointing out - the advantage likely to accrue from the ufe of the fulphuret, to the na- tion, and alfo the faving to the indivi- dual. By the information I have had from the Cuftom Houfe, it appears that the average importation of pot- afh, pearl-afh and barilha, the laft twelve years, amounts to about 5066 . tons annually ; about one half of this, (2533 tons) is barilha. The average price of barilha the laft three years, has been forty pounds a ton, fo that the value of the quantity imported is 101,323 ON BLEACHING. 6j I bi ,3^3 pounds ; of this only half, or thereabout, I underftand, is ufed in bleaching, the remainder being con- verted into foap. Moft of the pot and jpearl-afti is confumed by the bleachers, and the average price of it the laft three years has been lixty-five pounds a ton, con- fequently, the value of 2,533 is 164,645 pounds. Hence it feems, that the quantity of foreign alkalies imported into the kingdom every year, amounts to 265,968 pounds j and that the quan- tity ufed in bleaching alone, amounts to about 215,307 pounds annually. The average price of brimftone for the laft three years, is about twenty- five pounds a ton, which' is at the rate nearly of two pence farthing a pound ; 68 ON BLEACHING.' pounds four pounds of brimftone, and twenty pounds of lime, as already obferved, will .produce fij{ty gallons of liquor. In this country, twenty pounds of lime may be valued at about four pence, fo that the bleacher may have the fixty gallons at the expence of IS. id. By what I could learn from diffe- rent bleachers, the common allow- ance of alkali for fixty gallons of wa- ter, IS fix pounds of barilha or four pounds of pot-afh at the very leaft, and moft bleachers ufe more than this. The price of four pounds of pot-afli at the rate of fixty- five pounds a ton, is about two fliillings and four pence, which is two pence more than double the price of the fulphuret 5 but as the brimltone inuft be ground, an allow- ance ON BLEACHING. 69 ance fhould be made for it ^ and be- ing eafy of pulverization, a farthing per pound is an ample confideration for the expence attending it. The faving of fuel only remains now to be taken into confideration j and as this cannot be calculated with any degree of accuracy, I fhall con- tent myfelf by particularizing fa6ls. In the firft place, but fixteen gallons of liquid are to be boiled in preparing fixty gallons of the fulphuret, ' while the whole fixty gallons muft be boiled when the alkali is ufed ; hence it might appear that two thirds of the fnel are faved in the quantity of liquor, but it is not quite fo much, fuppofe we eftimate it at one half, which is rather under-rating it. Let us add to this the time necefTary to boil the different ON BLEACHINGi different liquors; the fulphuret rC“ quires but about half an hour, and the alkaline lixivium at the very leaft, feven hours to boil the linen in it, which is in the proportion of one to fourteen. The faving altogether to the bleacher from this ftatement, is obvioufly very confiderable ; and as the Wicklow copper mines are fufficient to fupply the whole kingdom, or indeed two fuch kingdoms with abundance of fulphur, let the confumption be ever fo great, the entire of the alkali, or 215,307 pounds muft be annually faved to the nation. But'fuppofe two thirds only of the quantity of alkali generally con- fumed in bleaching were difpenfed with ON BLEACHING. with by the ufeofthefulphuret (which is a fuppofition not warranted by my experiments) ' ftill the faving to the nation and to the individual, muft evidently be great indeed. THE END. ^ f ’ • . *. :> '■ SJ-0 '«£6£nyc£Ni£|.