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of-as it is called—" boiling" the oil, that is, by subjecting the artists' colour-shops in London, and has found them it to the action of a very high temperature, to effect its almost invariably to be mere rescripts of the old formula, partial decomposition, or a partial or incipient destructive producing their effects, such as they are, through the distillation of it, and to aid such decomposition by medium of the action of the old, or variations of the oli, applying to it one or other, or all, of the materials just preparations of lead. referred to, these being selected variously and capriciously, The varnish-maker who (when not content with welland, as far as the writer has ever been able to discover, settled, i.e., old raw oil long exposed to air and light, without there existing among the operators the most nor content with refined or boiled,) would preliminarily remote notion of the real mode of action. The practice treat his own linseed oil to get rid of the mucilage and has always been, and still remains, a purely empirical | the colouring matter, sometimes treats the oil, cold or one. This, then, is the practice—that of boiling linseed warm, with acetate or protoxides of lead, then sometimes oil to make it dry—that has so long, and still (with separates all lead by sulphuric acid ; sometimes he warms but one or two exceptions, to be hereafter mentioned) the oil along with sulphate of zinc or some salt of universally exists in England. In most large towns or alumina, or applies to it chlorine or some chlorine commanufacturing localities, as in London, in Hull, in pound, &c. "But the issue of the whole is, that the Liverpool, in Leeds, in Newcastle-upon-Tyne, and in varnish-maker still requires something better, that is, an Bristol, exists one or more oil-boiling establishments, oil unchangeable in colour, under the high temperature, where in some huge boiler, holding a few pipes or tons, needed to dissolve the copal and other gums he has to is placed the oil, along with the modicum of litharge and mix with it, and that after all shall remain a fine drying other materials; and a strong heat from a fire, acting exter- oil, and as free from colour as possible; this problem, the nally, is applied till the oil is “boiled ;” and this boiled varnish-maker has not yet solved to his entire satisfaction. oil constitutes the great bulk of the drying oil, whose The refined oil, in paint-making, is employed chiefly innumerable uses and applications meet us at every step as the vehicle in which to grind the white pigments. and everywhere, and for which, notwithstanding its The raw oil is used to thin and prepare for use the finer intrinsic defects, the demand is universal and immense. kinds of paints, from which boiled oil is excluded by its
The gentleman who this evening presides over this dark colour and a ter-effects. The raw oil is of itself a Society, eminent as well for his manufacturing and very slow drier. The refined is still more imperfect in commercial enterprise as for his scientific acquirements, this respect and herce, to quicken the work of the is himself one of the largest (if not the largest) manufac-operative painter, arises the necessity for using, along turer of this oil in the world; but even were these with these two, spirits of turpentine or the compositions operations conducted everywhere with the same care, called driers. Could the raw, or, still better, the refined, be and skill, and results that are to be found and are made of themselves to dry with sufficient rapidity, or obtained at the works of Messrs. Blundell, Spence, rather, Ecould a fine drying oil, of an equally fine colour, and Co., of Hull, there would still exist, as there be obtained, there would then be no need for turpentine now does, an urgent and universal demand, created as a drier (it would be used to produce certain art effects by the vast advances in art and art manufactures in only) nor for driers nor for boiled oil. every other direction, for something better and beyond! It is necessary to examine in some detail the existing this—for finer and for a greater variety of drying oils, for process of boiling, and its results. The oil to be thus better rates of drying, better colour, or greater varieties of "boiled," as it is called, is placed in copper, or boiler colour, and different degrees of limpidity or viscidity, to plate, or sometimes in cast-iron pans, of greater or lesser fit the various tangible but indescribable requirements capacity, according to the magnitude of the works; and of the artist and the operator, for better methods of pro- this capacity may be that of one pipe of oil, or of four ducing them, and for the kind of labour to these ends or six, or eight pipes. On an average, they hold four to with which this paper is concerned.
five pipes, or about two tons of the oil. Along with the Linsced oil appears in four different forms, from one oil is mixed so many pounds of litharge, of red lead, and or other of which the manufacturer, the varnish maker, of sulphate of zinc; sometimes of acetate (sugar) of lead, and the painter, and the artist, must, each for himself, select umber, or other matters, according to the peculiar notions it, according to his special requirements. These kinds of the “boiler," so-called, par excellence, from the geneare-1st, the oil in its natural state, as it comes from the rally long experience such functionary has had in such seed, and called raw oil ; 2ndly, this raw oil refined, or work, or in the establishment he is attached to. He is from which has bcen separated its mucilage and colour- generally some old and valued servant, pre-eminent ing matter; 3rdly, the raw oil boiled, that is, made or alike for faithfulness to the interests of his employers, intended to be made more drying than the original oil; and devotedness to the antiquated secrets of his craft. and 4thly, the raw oil put into the variety of conditions He is the very model of some old, honest, and enthuas to thickness, colour, and rate of drying that, in com-siastic alchymist, reduced to the inglorious proportions paratively small quantities, is to be found among the of a modern operative on wages, who roasts linseed oil, varnish makers, the artists' colour dealers, and others. I that he may unwittingly destroy any valuable property
The oils of the artist class, it may at once be re- it possesses, but which would remain unaffected, would marked, have generally more the character of curiosities | he only deal with it more gently and tenderly. than of utilities, and result from the fondling and nursing To the bottom of the pan, so charged, is applied a fire, of a gallon or two of the oil over many weeks or months, and the oil, with its contents, gradually raised to a high sometimes exposing it to air or sunshine, sometimes temperature. There is first thrown off some water, held wreating it with acetate of lead, or with litharge, &c. combined probably with the mucilage in the oil, and this Each artists' colour-maker has probably his own special water forms a yellow-stained froth upon the surface of mode of treatment, and not un frequently the artist him- the gradually heating oil. As the heat increases, there self prepares his own oil by some favourite method. The are thrown off, successively, acetic acid, acroleine, and result is generally that such specially prepared oils are by other vapours and gases, that give to this oil-boiling ro means remarkable for their drying properties; and the operation its distinctive but disgusting accompaniments, strongest the writer has met with he found to consist and make it needful that such establishments should be chemically of a solution, in any excess of oil, of the oleate exiled beyond the limits of refined or civilised habitaof lead, and it had obviously been made by heating raw oil tions or existences,—in London, to take refuge in Roalong with litharge and water, and afterwards expelling therhithe, on Bow-common, or in the Isle of Dogs; in by heat the excess of water used. This kind dried per se Hull, in Wincolmlee or at Sculcoates; and in Liver. in 15 hours.
poal or Leeds, in some similar locality and association, The writer has carefully sought for and examined the where, in close juxta-position with operations on a large kinds of alleged quick-drying linseed oils to be found in scale for manufacturing resin oil, for refining fish oils, distilling coal tar, bone-boiling and grinding, and the decomposed by heat, with safety. It, moreover, conpreparation of nameless manures, it is hoped that any tains, besides the oil of the linseed, other oils, such as process of olfactory analysis of the issuing abominations that of the dodder seed, and others not prevalent in the may fail in detecting those that especially belong to this north of Europe, and which are non-drying under the old boiling of oil. And even in such exile, the rest they treatment; and hence has arisen a conviction in the enjoy is but an uneasy one, under the eye of some sanitary minds of such firms as those of Messrs. Earls and Carter, official, urged into zeal by some rival interest, or by the of Liverpool, where the writer experimented especially real or imaginary spread of chemical knowledge in the upon these oils, that, on the grounds of this change in the community.
character of the oils in the market, as well as upon other It is needless to say here, that on the lands of the grounds, some modification or total change from the old highest class of houses, where there is at hand every modes, both of refining and of drying, should be sought needful appliance, and is ever exercised a most care ul for. The Messrs. Sissons, Bros., of Hull, not long ago regard for public interests, these boiling arrangements informed the writer that a large batch of linseed oil, conare so made as to minimise and place below nvigincetaining a large admixture of East India seed oil, which point the exterior evils of such a process; but wherever they wanted to boil in the usual manner, had so frothed the oil is so treated, the occurrence to a greater or less ex- up and swollen upon the application of the heat, that a tent of these nauseous emanations is inevitable.
large quantity overflowed through an outlet safety-pipe, Before the heat so applied to the pan has fulfilled its and was wasted, whilst the remainder was so thick, work upon the oil, the temperature of the oil has risen | and otherwise spoilt, as to be unfit to be applied to any to some 600 or 700 degrees of Fahrenheit. Finally, it ordinary purpose. As these gentlemen remarked, a rehas suffered the changes peculiar to its incipient or par- | petition of such accidents as these, though in their large tial destructive distillation, and passed from the brightestablishment of no moment, would be of serious importyellow colour of the raw oil into a deep and permanentance to the smaller houses." reddish-brown colour; and the more intense this dark Involved in these topics is a question of health, now colour, the better is the boiling considered to have been prominently before the public, viz., the lamentable disaccomplished. Upon an average, about ten or twelve eases and life-shortenings entailed upon the operatives hours are occupied, from the first application of the fire, in lead and the preparations of lead, among which pretill the oil is in a condition to be still further cooled parations must necessarily be classed the kind of oil we and transferred to the settling or store vats, whence, are now speaking of. For a principal element of modern after some days, the clear oil is decanted from the sedi- paints, viz., the carbonate of lead (white lead), there is ment (called •* foots”), and is in a state to be sent out as now proposed to be substituted another substratum, viz., boiled oil.
oxide of zinc (white zinc), and hence has arisen a conAnd what is the cost of this operation-of the ma- tingent necessity, if we thus shall banish preparations of terials the fuel and labour used—and what the ultimate lead from the pigment, to banish lead also from the value of the clear oil and of these “ foots?” What the vsual vehicle—the drying linseed oil. The vehicle drying rate and extent of the application of this dark- so used should no', if we would follow up this movement coloured oil so obtained? And is there no other method fully, be itself, as it now is, and has always been, because of giving to linseed oil the same or more perfect drying of the lead in the boiled oil, the most immediate agent and other properties than those realised by an operation of those evils thus sought to be avoided. Manganesed so antiquated and impotent?
oil, that is, the deep red coloured oil, or boiled oil, made The clear oil so obtained, even when from the very by boiling linseed oil with peroxide of mhanganese, which best makers, always contains a considerable quantity of I alluded to before, is, both because of its deep staining lead, is dark coloured-almost black, and does not, on colour, and of its imperfect drying properties, virtually exposure to air, materially bleach. It either, under the useless to this end. Oxide of zinc, per se, possesses no most favourable conditions, develops, on drying and ex- drying properties whatever; therefore, its mixture with, posure, a dirty yellow or yellowish brown colour, or it merely raw or refined linseed oil does not result in a blackens, through reactions between the lead in it drying compound. and sulphuretted hydrogen. In paint-work, its original All kinds of existing “driers” contain and depend dark colour limits its application to coloured paints. upon lead for their drying powers. How then is From all whites, and the more delicate tints of all in- this projected substitution of zinc for lead to be terior decorations and artists' work, it either is, or should aided by any method that, without lead, shall dry the. be, absolutely excluded. Its rate of drying, per se, is, on paints so composed, or give to the vehicle the rate of an average of the best kinds, 15 hours; but, more gene- drying that is practically essential. Should it be one of. rally, when taken from the smaller makers, or from the the results of these researches, fully (as it really is, shops, this ranges between 24 hours and 60 hours, and, and is submitted to this Society to be) to have solved, too frequently, it does never properly dry.
this problem, the writer conceives that this will not prove But the process is an evidently dangerous one, as the to this Society the least interesting part of his labours. application of a naked fire to vessels containing such He would, however, remark that the perfect innocuousinflammable matters must always be, and the fire risk in ness of oxide of zinc on animal life, has yet to be such establishments is proportional. It is an intolerable fully demonstrated ; and the gradually increasing deand daily increasing nuisance, both from fire risk and velopment of this branch of manufacture will speedily from smells ; whilst the giving, by this treatment, in- show this. It is however due, meantime, to say, that creased drying powers to the oil is never certain. It whilst the hideous and time-detested evils of lead are ends as often, in some hands, in utterly spoiling the oil indisputable, nothing has yet transpired similarly crimi. as it does in improving it. The gradually increasing native of zinc. importation, stimulated by the late war, into the market But a movement of this kind will not be aided by of linseed oils obtaired, not as of old, from the Baltic, overlaying its evidences. As to the evils alleged to be but from East India seed, has introduced into the old inflicted on the inhabitants of dwelling-houses that are, process a new element of uncertainty and of probable loss. or have recently been, painted with lead-compounded The difference of climate or of culture gives to the paints, worked with lead-impregnated oil (this boiled” Baltic and to the East India seed oil so different a oil), or dried by addition of lead-compounded driers, character, as to require and call for an entirely new it is only proper to say, that they (that is, the imputed mode of chemical treatment, not only in giving it in- evils) are not due to the lead in this case. There is no creased drying properties, but in refining and otherwise emanation of lead from the freshly-painted walls that applying it. This East India seed oil is what is called can be inhaled, or that otherwise can come in contact si tender.” It cannot be “boiled,” that is, incipiently with the persons of the inhabitans. It is to the turpentine used to thin, and to aid in drying, and which, being to it any required degree of limpidity or viscidity highly volatile, and carrying with it (not lead, but) cer- that will fit the multifarious requirements of the matain products of the decomposition of the oil, that other-nufacturer and artist; and to accomplish this at wise would go on imperceptibly and innocuously, im- pleasure, with or without the adjunct of preparations pregnates the air of the apartments, and is inhaled, that of lead, thereby either to meet such requirements as the head-aches, the dyspepsia, and the indefinable sense the old habit and style of oils may still perpetuate, of disorder, discomfort, and depression, in a newly- or to meet the growing convictions that a more harmpainted house, are chiefly due. Here, to the inhabitants less class of paints and paint materials should be merely, there is brought about no actual contact with adopted. the lead. Those who actually handle the paint are the persons who suffer—the operative painter, and the
II.—Review of Known Resources for Solution. operative manufacturer of the lead pigments, of the lead For the pure chemistry of the oils and of fatty compounded driers, and of the boiled oil.
matters it is needless here to say, that the chemical The scientific vigilance of the French Government world was, and is still, indebted chiefly to the researches takes care to propagate everywhere such knowledge, of Chevreul, undertaken and completed some forty bearing upon the physical welfare of its people, as che-years ago; and that it is singular how completely mistry or physiology may bring to its notice; and, these researches and their results have both fixed the among the rest, they encourage in every way the character of this branch of chemistry, and either prespreading abroad among the operatives a knowledge of cluded or obviated subsequent inquiry. But the labours the sad evils entailed upon them by handling and of Chevreul went to determine their chemical constiworking with pigments, paints, and other preparations tution, not to investigate their peculiar changes under containing lead. And the writer has just been told, by all kinds of extraneous action; and the peculiar cheone well conversant with Parisian proceedings of this mical history of the changes the drying oils undergo kind, that the Government will now admit of no con- under the various conditions here concerned, formed tract for public works for paints that contain lead. no part of his admirable researches. Both the manuThat, although prohibitively to restrict the use of facturing and the chemical world have, in this case, these is beyond the sphere of an Imperial decree, by pro- seemed content to accept as a sufficient explanation ceedings so significant as this of their contracts, they that of the oxygen absorption, without thinking that instruct and intimate the importance they attach to the this fact might be only one of many actions simultasubject.
neously at work, or of a series of complicated changes, The oil-boiling trade in England is divided chiefly be- each of importance, and requiring to be studied before tween two classes :- the paint manufactures and grinders, the subject could be understood, and this understanding who boil oil for their own use and for their own sale, be brought to bear upon any processes for improving inand the oil boilers and refiners, who receive from the oil dustrially this branch of manufacture. The more modern merchants and from consumers—not themselves boilers, organic chemistry, with its accurate manipulations, and the raw oil, put it through the operation, and return it at the blaze of light it has and will yet throw upon this and a certain charge per ton. Those of the former class, kindred subjects of inquiry, has hitherto in its brief generally, in every respect, persons of high character and career had too many other objects to be devoted to, or so position, have obviously every motive of interest, had few real workers to undertake them, as to have passed they none other, to do their work well ; but those of the over almost entirely this mere section of so large a field. latter class (with many most honourable exceptions) have The result has been that this question of the phenomena so conducted the business as to reduce it to a most dis involved in the drying of oils had not yet passed through reputable position. By some of these the oil sent them the ordeal of the minute and complete examination is sometimes never boiled at all. It is coloured in some moderu organic chemistry was capable of effecting, and way, and returned at a charge of from 30s, to 40s. per consequently there had been made no inroad upon either ton. In other cases, a hundred weight or two of the the old theories, or upon the facilities of testing the oils genuine raw oil is abstracted, and its place supplied with in order to improve their drying properties, that the daily an equal weight of common resin. In others, the abomi- and vast importance of the subject would seem to have nable addition is made to it of a quantity of resin oil. / merited. If it be known to be for export, and the chances are The existing practice, that has been described above, is against any examination before departure, any descrip-itself of course older than the comparatively more recent tion of refuse stuff, in no other way saleable or usable, will alleged explanation of its chemistry. It is older than the be mixed with the genuine oil; and in due time, some time of Scheele and the epoch of the chemical philosophy victim, in one of our remote colonies, finds the paint it has of Lavoisier; for oxygen and its reactions, real or supcost him so much money and care to provide never dries; 1 posed, in the case, were not known or recognized for so very pleasingly, of course, convincing him of the im- iong a time as litharge and its reactions upon oil have proving moralities of the mother country. The practical been. But both the practice and its chemical explanaevils of such a system are met with daily and every-ation are sufficiently antiquated to have led to the hope where.
that the application to the phenomena of this branch of To relieve a wealthy and most important class of industrial chemistry, of the laws and appliances of persons from this abominable system, by providing them modern organic chemistry, would surely result (as in (each for himself, if he wish) with the means of treating so many other instances) in throwing some light upon, their own oil on their own premises, saving both carriage, or in giving a truer and more satisfactory interpretation boiling charge, and the chance of deception, and pro- of, the chemistry involved in them. ducing oil of any colour and quality that may be But mere analysis did not furnish the information required, is another of the practical results of the re- sought for. The expression, in correct formulæ of the searches this paper is intended to submit to the Society. composition of the linseed oil, in its original normal
This, then, is the problem-to take the raw oil, and condition, as obtained from the seed, and a similarly by some process, free from danger, fulfilling its objects at accurate expression of its composition, when it had bean ordinary temperature, or, at most, under a steam heat, came solidified, threw no light whatever upon changes free from noxious or unpleasant accompaniments, simple, I whose intermediate character, or the character of the cheap, and expeditious—to give to the raw oil an series of results intermediate between the normal and efficient rate of drying property that can be modified at final condition of the oil, were probably as important to pleasure ; to give to it any colour, ranging between the the end in view as the original and the final conditions dark brown of the old boiled and the straw colour of themselves were. the refined, or a better, if that be possible; to give Analysis, therefore, would not, and did not, supply the required information, and a totally different line of some phenomena will issue that shall give the crucial experimental research was demanded.
indications sought for ? But, amidst such a multitude of phenomena, that must To test the drying rate of an oil, or of an oil mixed surely be presented, if only sought for, among the with some pigment or material to dry it, it is simply almost infinite number of mixtures, in daily use, of lin- necessary to spread it upon the surface of glass, and exseed oil with other substances, are there not already ex-pose it to the atmosphere, and to note the time occupied isting, and to be discovered, without the making of spe- in its passing from its fluid to a solid state, or in drying; cial experiments, such reactions, or indications of re- and the circumstance that on its being touched with the actions, as shall give, in the apparently complicated sub-finger, it neither adheres to it on removal, nor resists ject, the crucial direction sought for? What kind of its removal (that is, not being “ tacky"), is taken as paints, with linseed oil as the vehicle, dry the soonest of evidence of its being dry. It is needless to say that even themselves? What kind of substances used as the pig- this simple method involves the necessity for some prement are thus found to retard the drying of the oil? cautions, always, in one shape or another, due to accurate What the chemical actions to be discovered in the experimenting. The oils, in comparative trials, must be peculiar mixtures of materials that the operative painter spread out of a uniform thickness, or the same weights has, in all times, been using to act as driers, each opera- or measures spread over an equal area, and each must be tive, as is well known, having for himself some favourite placed in exactly the same conditions as to temperature, specific of this kind? What the modus operandi of the exposure to light, and to currents of air, &c. The drying mixtures, springing originally out of those operative rate of an oil is materially affected by temperature the painters' empirical trials, that are now so generally ma- hygrometric condition of the atmosphere, by its state as nufactured and sold as driers ? What is there in these to stillness or motion, and by the presence or absence of that begets a specific action so singular as the addition to sunlight, &c. An oil that in a warm, breezy summer's paints of only some very small per-centage of these, re-day will dry in 8 or 10 hours, may not dry in less than sults in the paint so treated, drying in from 12 to 18 16 or 20 when the air is foggy and motionless; and in an hours, whilst, without such addition, the same paint unfavourable winter's day may not dry in less than from may not dry in from 60 to 70 hours? How explain all 24 to 30 hours. But in all after-reference to drying this or how can such mixtures be made to develop any rates, it will be understood that those stated are obtained chemical facts that may serve to throw light on the under average circumstances, as with the temperature of subject?
the air at 60° Fahr., &c. But with regard to these and An analytical examination of those mixtures showed similar minute details that these experiments have rethat the foundation of the whole was the oxide of lead, - quired, however essential and interesting to the exlitharge. That in the most potent kinds there was also perimenter himself, it would be altogether out of place, acetate of lead, mixed variously with sulphate of zinc, and beyond the patience of this Society, to do more than sometimes with red lead superadded as the active agents, thus merely allude to them; but this method of testing, united with sulphate of baryta, with carbonate of lime, it will be understood, is that adopted and referred to sometimes with caustic lime or with sulphate of lime, throughout this paper whenever the drying rate per se as the non-active and bulk-making elements, added in of any oil is mentioned, that is, its rate of drying when some cases to modify the action of the others, but most tried alone and unmixed with any other substance. When frequently to give weight and profit. These, in various wished to test its drying, not per se, as in the case just proportions and ground up with linseed oil, raw or stated, but under conditions of a more extended expoboiled, in a peculiar order of addition (the peculiar effect sure to air, brought about by its mixture with some maof which these researches hereafter explain), constitute terial not itself acting chemically, but mechanically, then the driers of the shops of the present day.
this further condition of the test is obtained by grinding But the result of an examination of those, founded on the oil up with oxide of zinc for a white, and with analysis, developed only the fact of the agency, in some lamp black for a black, on glass as before. When so unexplained mode, of the same agents that had always mixed there comes into play other actions and effects, to been employed to give such potency as can be given to be hereafter more particularly referred to. the drying power of the oil when boiled. It was but The first series of experiments was occupied with the the ringing of the changes upon the old materials, and the oil in its normal condition, and with which there was old method of reasoning; but in the issue of which (that mixed nothing but the material whose specific action or is, in those driers) were empiricism had, in the usual effects (if any) upon its drying properties was to be way of accident, developed better and more active ef- determined; and this specific action was sought for fects. There was still no satisfactory clue to the real under two several conditions as to temperature; the cause of the specific action upon the oil of these mixtures, first under the ordinary temperature of the atmosphere, nor, consequently, any light thrown through which to (that is, the ordinary conditions that oil in the form of devise better and less objectionable modes, than that of paint or varnish is subjected to) and the second under drying paint through the medium of these compounds, conditions of the application to the oil, along with the or of giving to the oil itself better drying and other es- several matters added to it, of higher and various sential properties than those obtained by the ancient degrees of heat. and most objectionable method of boiling it.
The immediate issues of both series of experiments
were sufficiently curious and interesting; but it would be III.-Method Chosen for Solution.
trespassing too far upon the indulgence and patience of The course adopted was that of multiplying experiments this audience to recapitulate other than the main results, under conditions so completely comprehended and at com- Along with 100 parts of the oil were ground up (using mand, that the effect of each element of the trial should a slab and muller of glass) respectively 5, 10, 15, and 20 be apparent at first view. It was the simple plan of parts of the substance whose action upon it was to be bringing into contact with linseed oil every conceivable found out, and these mixtures, spread by a camel's hair material, and watching carefully the results, viz., the pencil upon plates of glass (non-absorbent) and the time issues of reactions, as seen or expressed in the one simple of drying of the oil, (or the length of time during which result of the oil drying, or being impeded in its drying, it did not dry,when that negative result followed,) together under the specific action of each material; to take every with any special appearances, and the attendant hygromaterial that chemistry can supply, and casting aside for metric condition and temperature of the atmosphere the time all mere theorizing, whether the old doctrine of duly noted. oxygen absorption, or any other, to rely solely upon the In this manner were successively applied to the oil inevitable though slow issue of trial, narrowly watching such substances as the various oxides and salts of tin, the results. Surely out of such a course of experimenting, those of antimony, of copper, of arsenic, of zinc, of lead, of cobalt, of nickel, of manganese, of tungsten, and or disturbed ; and to watch under the microscope, and numerous others. There were also applied alumina, determine the amount of this action or influence, and lime, soda, potash, magnesia, sulphur, ammonia, and the kinds of mixtures that best produce it, constitutes their salts of every variety, and varied in every way by by no means the least interesting of the curious phenousing them (both these and the former) in their dry mena developed in the course of these experiments. (i. e. anhydrous state, and with their constitutional water and their water of crystallization in every instance
IV.- Results and Dedi ctions. on which they assumed or were capable of being placed Confining a brief summary of results to the main obin these different chemical conditions. In like manner, ject in view, those sugsestive of the manufacturing opemoreover, was the oil submitted to the action of iodine, of rations to be adopted, and omitting a variety of instrucbromine, of chlorine, of cyanogen, of sulphurous acid gas, tive and curious phenomena thrown out in the course of and the gaseous oxides of nitrogen, and others, and also, of so much experimenting—such, for example, as the pecourse, to the more readily obtained action of the hydrated culiar texture of paints, or surface appearances when dry, acids, the acetic, the sulphuric, the oxalic, the hydro-produced by unusual mixtures of materials; the various chloric, and the nitric.
degrees of " gloss,” and of “flat,” unexpectedly deveExperiments so ordered were multiplied into hundreds ; loped, and suggestive of new modes of producing these and the first conspicuous results were to reduce to only effects; the curious phenomena of molecular disturba mere few the materials that out of all these had any ances, already alluded to, when watched under the mispecific action at all of the kind here sought for or desired, croscope, and yielding curious art effects, that an artist, viz., a drying action, unaccompanied by any other action provided with sufficient chemistry and his microscope, that precluded the application of the agent so effecting and who would penetrate into some of the inmost reit to the purpose in view. The result is indeed finally cesses of the chemico-mechanism of his craft, might con(as will be seen afterwards) to reduce this number practi- vert into a study of infinite interest and utility; omitting cally to two or three, because these peculiar actions, fitted indications of the pure chemistry of the successive exactly, and better than any others previously em- changes in the oil, yet to be thoroughly determined, and ployed, all the requirements in drying oil in its various expressed in accurate formulæ-omitting these, and many applications; and the next conspicuous result was to show others, the summary of practical results may be given that such of the above substances as did exercise this briefly as follows: specific action, were equally effective when either the When an oil, or an oil paint, on exposure to air, dries, smaller or the larger proportion was used, that is, the oil four distinct kinds of action come into play, to effect, or dried as well under the action of the 5 parts to the 100, to contribute to, that result. These areas under the 10, the 15, or the 20 parts, and that, there. Firstly-The chemical actions taking place naturally fore, this action was not of a kind belonging to that class (and unaided by any other contingent action) between of chemical actions depending upon reactions between the oil and the atmosphere, and atmospheric influences, elements in equivalent quantities, but of some other and / or the natural chemical action consequent on exposure. yet undetermined kind.
Secondly.-Those due to some specific chemical acThis series of experiments was followed by another, in tion upon the oil of some element in the pigment, or of which, instead of using the several chemical substances some element added to it specially to initiate or aid the alone, a variety of compounds, mutually reacting with action that follows upon exposure, or the induced cheeach other, were mixed together along with the oil, and mical action, as contra-distinguished from the natural. their mutual or contingent reactions upon the oil clearly Thirdly.-Those due to the peculiar physical structure noted ; and it was out of this latter series that there came of the composition of the paint, through which, within finally the processes which it is more especially the object the same superficial area, a larger surface of the oil is of this paper to submit to your attention, and that, in the brought under the action of atmospheric agencies. judgment of the writer, are destined to act in future so Fourthly.-Purely mechanical actions, brought about important a part, both in improving the processes to be by molecular disturbances in the oil or paint, by which applied, to the treatment of these oils, and because of the fresh particles of the oil or fresh surfaces of it are extraordinary results in the qualities and varieties of the being, during the time of exposure, continually thrown oils so obtained, in thus extending the sphere of the ap- up to the action of the atmosphere, by which the atplication of drying oils.
mosphere is admitted interstitially as well as superAnother long series of experiments, (still conducted ficially to act upon the oil. These molecular disturon the same general principle of searching, by multiplied bances are caused by the admixture with the paint of trials, and out of the consequent multifarious results, for some volatile fluid, as turpentine, and its evaporation;new or crucial phenomena), had for its object to discover by the escape of water of crystallization of some salt how results obtained under the former series, when the ma- / or other added to it; or by chemical re-action and comterials whose specific action upon the oil was investigated, binations taking place between the elements of the pigper se, were modified, when, in addition to the drying com- ment, or between it and some other, or between some pound, or the compound whose drying or conirary action other elements added, and resulting in the formation of was to be determined, there was mixed with the oil some some new compound, or in some act of crystallisation material intended to bring the mixture into the con- or other changes of form ; and often in the liberation dition of an ordinary paint, so far as regarded the relative of previously combined water, &c., &c. The materials proportion of the oil and of the pigment; and the pigments whose re-actions yield those purely mechanical actions chosen for this purpose, to mix with the oil, or along are, of course, such as do not, of themselves, act chemiwith any other experimental material added to it, were cally upon the oil, but act simply by creating in it a as already mentioned, the oxide of zinc and lamp-black, movement of its particles during the time of exposure used, of course, separately and comparatively.
of the paint for the purpose of drying it. To this series was added another, intended to determine In any instance of an oil or a paint drying, the inthe character and amount of action of another kind that fluences at play to contribute to that result can be traced the former series had given traces of, viz., the purely me- to one or other, but most frequently to the combined chanical action (not chemical) caused by materials effect of two, or of all of those kinds of actions. mixed with the oil, mutually 'reacting among them- If a given weight of any drying oil be spread in a thin selves, and, in 'so reacting, giving birth to a molecular filin over a given area-say 100 square inches-it may action or disturbance of the oil, and thus causing it con- dry in (say) 20 hours, under the natural chemical action tinually, during such action, to present fresh surfaces of the of atmospheric exposure and influences. oil to the action of the air. An oil so mixed and If oil of the same kind and weight be ground up to subjected dries much sooner than one not so agitated the consistency of an ordinary paint, with some material