and simultaneously in all degrees of dilution. Most reagents are used in such small quantities that a stock for more than a year's service may be kept in specimen tubes of the smallest sort. Hydrofluoric acid and ammonium fluoride may be conveniently kept in similar tubes of ebonite, in the caoutchouc stoppers of which thin platinum wires may be conveniently fixed, coiled up at their free end into a loop or a spiral,

The selection of reagents, even if arranged for all contingencies, takes up little room.

Operations.

The evaporation of dilute solutions is generally effected on the object glass. If high concentration is necessary, the solution is let fall, drop by drop, upon the heated spot of the glass, by means of a small pipette. A current of dry air expedites evaporation and prevents boiling. When the last drop is about half evaporated the object slip is quickly cooled. The partial evaporation of single drops is often requisite, and occasions much trouble to beginners. A thin glass and a small flame are the most essential conditions. The object slip must almost touch the point of the flame, and the refrigeration must be effected as quickly as possible. By means of the following simple expedient it is possible to evaporate the smallest drops over a free flame without the danger of their entirely drying up. Upon an object slip, and near one end, there is laid a covering-glass; the drop to be heated is placed upon this, and heated as usual over a small flame. When he proper degree of evaporation has been reached, the covering-glass with the remainder of the drop is made to slide upon the cold half of the port-object. Evaporation by heating the port object always invariably occasions the formation of irregular crystals on the edge of the drops, and this evil is the more perceptible the further the heating extends over the glass. Evaporation at the ordinary temperature (e.g., in an exsiccator) generally produces uniform crystallisation; the same is the case if the glass is cooled and the drop is heated by blowing warm air upon it from the nozzle of a blowpipe strongly

heated.

For sublimations the specimen is placed near one of the corners of the port-object and covered, after it has been moderately heated, with a shorter slip with its corners bent downwards. For sublimation at a red-heat, and for subliming fluorides, we use small platinum spoons covered with platinum foil or covering-glass. The necessary cooling is effected in this case by the application of a drop of water. For filtration there are substituted, as far as possible, decantation and absorption with filterpaper. It often occurs that a drop of liquid must be separated from crystalline or powdery sediment without the necessity for complete clarification. This can gene. rally be effected as follows:-A clear portion at the margin of the drop is drawn out into a streak of 1 c.m. in length, and its end is gradually widened to form a drop. The speed at which the liquid streams over depends on the inclination of the port-object and on the expansion of the thread of liquid. The rest of the liquid is drawn away through the connective channel by means of a platinum wire held in a slanting position, and intercepted with a small roll of filter-paper. The washing is effected in a similar manner, small rolls of filter-paper serving to suck up the rest of the washing water. If complete clarification is needed, or in case of light flocculent precipitates, such as basic iron or aluminium acetates, the iquid may be allowed to subside in a tube pipette of 2 m.m. internal diameter, the upper end being closed with a wax plug. The deposition may be hastened by the addition of washed barium sulphate during precipitation, and by centrifugal action. If the liquid is sufficiently clarified allow it to flow, drop by drop, upon burnt clay or compressed filter-paper. Here it forms little lumps which can be washed with a couple of drops of water, and scraped off with a slip of sheet platinum. (To be continued).

THE PROGRESS OF CHEMICAL THEORY: ITS HELPS AND HINDRANCES.*

By Dr. PERSifor frazeR, Prof. of Chemistry.

IT is the ordinary reproach to science of the ignorant and disingenuous, that its conclusions at any given period are no more stable than the wildest speculations of the fanatic and dreamer.

We read continually in the papers some arrant nonsense said to have been pronounced by "one of the eminent scientists" of such-and-such a place and time, which the course of events has disproved; and the public is left to the conclusion that the gains of science are only air castles certain to dissolve when they become unpopular, and certain to lose popularity when the first pleasurable effect of the announcement has passed away. The following extract, from the St. Louis Republic, will furnish a case in point:

46

It has only been sixty years since a great mathemati cian demonstrated that a steamship could never cross the Atlantic because it would be impossible for her to carry enough fuel to last during the trip. Before he had hardly deduced his calculations a steamer from America glided into port."t

The name of the eminent scientist is not mentioned, and it is safe to conclude that if any man made such an observation he either would have failed of recognition by the class to which he is said to have belonged, or he was false to the fundamental principles of inductive science. It is not the province of inductive science to establish what is impossible, but what is in various degrees likely. Its premises are facts and its conclusions are probabilities; in many cases weak, but in others so strong that they produce the same effect upon the mind as certainties. Nor is it true that the gains of science are evanescent. Parallel with the accumulation of observations run the generalisations upon them. These generalisations are usually passed through the purgatory of hypothesis before they attain the bliss of theory, but no theory is old enough yet to have become more than a theory, though some have stood so many tests of their truth as to carry the conviction of axioms.

In looking over the histories of the sciences one finds the same general course of progress. At the outset in the halcyon days of the old Greeks, it is likely that some wise words will be found to have been spoken concerning them all; words that astound us with the apparent insight they show into problems which it would seem that the last twenty-five centuries were needed to give. But the centuries were not all equally productive. There came across the path of every systematic study of the laws of nature, first the cultured blight of the Aristotelian philosophy, which assuming to know everything, in fact largely contented itself with verbal jugglery, whereas accumulation of facts was the only road to knowledge; obliterating the forward steps that had been made, and substituting in their place the evolution of the universe and its laws from within. It was a philosophy where the distinction between words and things was obscured, and

* Introduction to the Chemical Lecture Course at the Franklin Institute, November 10, 1890.

+ In reference to the supposed steam engine prediction, Mr. W. P. Tatham calls my attention to the fact that the actual observation misquoted by the New York Herald for sensational or other satisfactory journalistic reasons, and repeated ever since (in spite of countless corrections), after the manner of the average erroneous newspaper paragraphs, was made by Dr. Dionysius Lardner and referred to the steamer of that epoch, which, according to his calculation, could only carry coals for a journey of 2000 miles, with due allowance for accident and delay. That he never entertained such language: "We are even now upon the brink of such improvements an opinion as that above referred to is evident from the following

as will probably so extend the powers of the steam engine as to

render it available as the means of connecting the most distant parts

of the earth."

The Steam Engine Familiarly Explained and Illustrated, &c.," by the Rev. Dionysius Lardner, LL.D., F.R.S., pp. 241-242, &c., &c. E. L. Carey and A. Hart, Philadelphia, 1841.

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a natural fact was attained by means of a pretty syllogism.

Vastly worse were the centuries which followed, known as the middle ages. Centuries of ignorance, selfishness, and crime; when the possession of any knowledge but that of an armourer was looked upon with distrust and ascribed to the devil.

The different natural sciences emerged from this barbaric condition one to three centuries ago, and under the liberty of enlightenment, with the stimulus of more general education, have attained an abode in the life of the race from which it is difficult to see how they can be displaced without such a general cataclysm as would nearly destroy the human race itself.

Amongst these sciences, that of chemistry has had such a marvellous career that it is, perhaps, the best example which could be selected of the progress just alluded to. It illustrates aptly not only the methods employed in building up an inductive science, but the things that have helped and those that have hindered a development which, nevertheless, in spite of all hindrances, must fill us with a sense of wonder.

Our reason for this is that from various causes the real growth of chemistry only began in the seventeenth century, and that even then it lost nearly a hundred years in the quagmires of a false hypothesis which not only directed the efforts of chemists into unfruitful fields, but destroyed the value of the conclusions they reached from their work. Yet, even with all these drawbacks, no domain of human investigation has been widened so rapidly and with such advantage to the world.

At the very outset of the subject we find a generalisation of old Democritus (who lived 450 B.C.) so astounding in its character and so accurate in most of its statements that only in the past few years have chemists been able to reach these profound thoughts thrown across the ages into the midst of the civilisation of our time, as the legend has it that Bruce's heart was thrown by the Douglas into the hosts of the Saracens to stimulate the ardour of the Christian Knights to charge and recover it. But, unfor tunately, no such effect was produced by the good old laughing philosopher; though at a snail's pace, and after a lapse of 2300 years, we have reached the spot. Briefly, as transmitted to Epicurus, and expanded by Lucretius B.C. 99-55, it was this.†

The universe consists of atoms and space. The atoms are of many forms and of different weights, and the number of atoms of each form infinite. Change is only the combination and separation of atoms! Atoms are in constant motion. "First beginnings" or atoms are never destroyed or worn out. The difference between a hard body like iron, and a soft body like air, is that in the first the atoms move to and fro within small distances; in the soft body they move freely or rebound from each other only at long intervals.

Bodies are partly "first beginnings," partly unions of "first beginnings." The properties of the bodies formed of the groupings of "first beginnings" need not be like the properties of the "first beginnings " themselves. "It matters much with what others and in what positions the first beginnings of things are held in union and what motions they do mutually impart and receive."

These views are extraordinary, and, with the exception of the difference in the form of atoms, which is a point beyond what we have been able to reach even now, the above contains a very fair statement of the atomic theory which is held by the most advanced chemists to-day.

How Democritus could have reached such conclusions is a mystery, but his annunciation of these recondite truths very well illustrates the fact that an hypothesis, be it never so beautiful and even true, if unaccompanied by

*It is intended to refer here to the exposition of the Aristotelian philosophy by its disciples from about the time of the Christian era to the eighteenth century, and not to disparage the marvellous genius of Aristotle.

+ Democrit-Aderita operum fragmenta.

facts to support it in no way helps the progress of natural science. Like every other guess it indicates merely the frame of mind of the man making it. It is like a floating shadow on the sea of time. Perhaps it defines substance, perhaps only a cloud of fancy.

This seed thrown off by Democritus found no soil of facts on which to grow, from his time until late in the present century, although Gassendi, Canon, and Provost at Digue, in France, after ages of ignorance, proposed it again, but without proof; and it is thought to have influenced the minds of Newton and Boyle.

This then is one example of an occurrence in the history of the science which to all appearance neither helped nor obstructed its progress unless in the indirect way of teaching men's minds to grasp large and comprehensive thoughts. All could not have been ignorance and degra tion in Abdera (Thrace), or Miletus, or Athens, where a language existed capable of conveying from mind to mind thoughts like these, and where a mind was capable of conceiving such thoughts.

It teaches the student of natural history a lesson in addition to that of the old traveller's speculations, and it may serve to illustrate the difference which the late Prof. Clifford of Cambridge pointed out between accepting those conclusions of natural science which one has been taught, but has not personally investigated, and accepting what is said to have been revealed, but which, it is acknowledged, is not susceptible of any proof. In the one case the way is open to any one to pursue any single direction which has been before taken; measuring and judging of the correctness of the steps of one's predecessor; but in the other case there is no path anywhere, and the correctness of the position assumed cannot be judged. It is the difference between, on the one hand, handing the keys of a hundred trunks to a custom house inspector, who has at best time to examine but one or two, asking him to satisfy himself of the accuracy of your description; and, on the other, telling him that something indescribable ought to convince him more thoroughly of the contents of the trunks which he cannot inspect than of those which he can. Speaking generally it may be said that a proposition of which the steps which led to its acceptance cannot be indicated and followed has no place at all in the domain of science, though it may be

true.

Such propositions were those of Democritus above given, and it is quite just that in the absence of logical proof they should have been excluded from the realm of science, and that to him who first showed reason for believing them should be accorded the honour of their discovery. Of much less importance is the next hypothesis of the nature of things which we find annunciated by Aristotle in his quadrilateral of states: solid, fluid, dry (or warm), and moist (or cod), or what he supposed to be the elements of all bodies, viz., earth, air, fire, and water. It was unfortunate, and yet in accordance with the usual march of events, that this utterly inadequate and narrow guess should have fettered men's minds for 2000 years, owing to the mighty hold which Aristotle took of all nations. (See Aristotle, "A Chapter from the History of Science," Lewes).

As his historian remarks, Aristotle's works had a prodigious influence in Asia, and Europe, and Africa; among the Persians, Arabs, and in Germany, where part of his ethics were read in the churches on Sundays instead of the Bible. In the middle ages, too, these elements of Aristotle were imbued with a mysticism more than Platonian.

It was the spirit of that middle age, when the ignorant classes being the powers, made patient scientific work difficult and dangerous, that learning was concealed under the mask of paradox and cryptogram as if it were a crime. Whatever Aristotle's view of his elements may have been, it took a new direction, beginning with Geber in the eighth century

The first chemists were alchemists who sought the

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his services were invaluable, as without them no further progress could have been made. This fact illustrates also the injustice of the cry so popular in some cases when the fallacy of a proposition has been exposed :"What have you to set up in its place?"

At the end of the fifteenth century the alchemists had added salt to mercury and sulphur. Many regarded the Aristotelian elements as the ultimate; and mercury, sulphur, and salt as the intermediate or proximate elements, as, for example, Basil Valentine, who extended the number of substances of which these were the ultimate elements, from metals to all known matter, but denied that they were the common substances which we know under their names.

In the early part of the sixteenth century the failure to find the philosopher's stone led to the decadence of alchemistical or transmutation chemistry, and the rise of iatrochemistry or that of healing. Paracelsus (14931541) taught that in a burning body the sulphur quality represented the inflammability, the mercury the sublimation, and the salt the ashes.

From this to the end of the seventeenth century disputes as to tenets were numerous, but no real progress was made, Agricola (1490-1555) attacked Paracelsus and fell back upon Aristotle. Libavius wrote the first treatise on chemistry (1595). Van Helmont (1577-1644) denied all Paracelsus' views and sought an universal solvent, which should be a panacea. He first recognised the existence of gases and quantitative relations, and opposed Aristotle's doctrines that fire was a body or earth an element; but believed water and air were such.

Glauber (1603-1668), though possessing variable views, invented better means for separating bodies. Sumert (1572-1637), Willis (1621-1675), Lemery (1645-1715) believed in five first principles-mercury (spirit), sulphur (oil), salt, water (phlegma), and earth. Lemery taught that these were in rapid motion, and thus gave rise to the obvious properties of things. He explained the wellknown phenomenon of the calxes of the metals weighing more than the metals themselves, by supposing that in burning they absorbed fire materials.

The real philosophy of chemistry commences with Robert Boyle (1622-1691), who denied the accuracy of the doctrines both of Aristotle, and the later alchemical and iatro-improvements upon them. He believed that heat had not the power to transform complex substances into their constituents, but, on the contrary, sometimes produced complex out of simple substances, and sometimes was without effect. Other agencies than heat could produce the same effects. He strongly denied that one could predict the number of simple substances as Aristotle and his successors had done. He thought it probable, however, that the so-called elements consisted of the same kind of matter, differing only in the size, form, &c., of their respective smallest parts (see Kopp's Geschichte der Chemie).

It is well to pause for a moment here to consider these logical and scientific views of Boyle, not alone because they introduced for the first time a rational inductive system of chemistry, emanipated from the mysticism and superstition of the ancients, but also because they are typical of one of the greatest of helps to the progress of chemical theory, independent and fearless criticism.

Except the brilliant guess that the so-called elements consisted of the same kind of matter, Boyle's mission seems to have been to hew down the weeds and under

Surely it cannot be required of him who discovers a flaw in a supposed explanation that he should be always ready with a sound explanation. The two characters of mind which are required to accomplish these very dif ferent tasks are entirely unlike.

Plato and Aristotle probably regarded the lightning stroke as a natural phenomenon, and could have refuted the popular belief that it was the missile from Zeus's hand, but it required dozens of centuries of observation before even the most remote approach to an explanation of the phenomenon could be given.

As soon as the ground is cleared of rubbish, other and more rational theories have a chance to grow. Therefore the iconoclast, if impelled by his sense of truth, and if considerate in his methods, is a necessary pioneer and axeman ahead of the great army of Science. It is so much easier, however, to throw down than to build up, that the iconoclast business is often overdone by those who are incapable of any more skilled service to Science, and who confound the art of attacking everything with the duty of overthrowing evil. All honour to Robert Boyle for calling a halt in the unbridled fancy of the chemists of his day, and clearing the way for a new era! All honour to his deep insight into the workings of Nature, that he announced independently what old Democritus had dimly foreshadowed 2000 years before; and what it was reserved for a great chemist now living to put in words and carry almost to the state of an accepted theory: yet to neither of them will belong the credit of demonstrating the unity of matter, but to some one, it would seem, who shall pass the speculative stage and offer proof. It looks as if this were not to be long delayed.

Both by Boyle's destructions and by his conceptions he aided the progress of chemical theory, as few have done since his time; and chemistry, or the study of the most intimate relations of matter, as distinguished from alchemy, magic, or the healing art, may fairly be said to have started with Robert Boyle.

Singularly enough the first sapling to spring up and occupy the new clearing made by Boyle was an error so gross that it seems to the youngest student of to-day grotesque in its clumsiness, and yet, defended by some of the subtlest of sophists, it took 100 years to overthrow it. And the most instructive part of its history is that it was finally overthrown by an argument which Boyle himself had employed, which had been employed by other sceptics, and explained away by the phlogistonists, and was ultimately and successfully refuted with the same experimental proof by a countryman of Boyle. It is often the case that an attack in front, over the very ground of numberless previous repulses, is successful, and it was the case here, as shall be briefly shown.

Stahl (1660-1734) was a physician of independent views, who adopted Becher's theory of combustion or the changeability of bodies by heat. He believed that he had settled experimentally this question:-" Is a common quality present in sulphur and carbon ? or is one contained in the other ?

The generally accepted view at that time was diametrically opposite to that which Boyle held of combustion, and might be stated thus:-Sulphur consists of oil of vitriol and some combustible body, which latter escapes in burning. Stahl combined oil of vitriol with an alkali, and, heating the combination with carbon, obtained an alkaline sulphide similar to that produced by sulphur and an alkali. From this, sulphur (or vitriol) can be separated.

Therefore, the combustible in carbon and sulphur was the same!

Heating calxes of the metals with carbon, there resulted the metals. The metals were then composed of the calxes and this substance. Fats and oils produced the same effect with the calxes, and, hence, in them too was the same combustible substance.

Stahl called this combustible "Phlogiston." This hypothesis was rapidly installed into the rights and dignity of a theory, and rallied around it, as such, some of the brightest and best minds for three generations.

It was not only faulty in its conclusions, but inadmissible in its steps, and should have incurred the opposition of every intelligent man who understood the limitations of inductive philosophy; but it occupied the vacant space left bare by the labours of Boyle, and, with a growth as luxurious as it was pernicious to the attainment of truth, obstructed in many ways all valuable advance of chemical theory while it lasted.

It may not be amiss, before sketching its rise and overthrow, to point out here wherein its inherent fallacies should have condemned this hypothesis from the outset. Hypothesis means a guess a temporary structure erected by the employment of the imagination strictly governed by experience, for the purpose of more rapidly reaching a generalisation than by waiting for all the facts which in the end will be necessary to sustain a fullfledged theory. After one or two facts bearing on a subject are ascertained, it often happens that the mind is directed towards the possible existence of a law which would explain them both; but numerous unknown and untried experiments must result in a certain way in order that this supposed explanation may stand.

With time and a constantly increasing experience mors and more such facts are ascertained. If all fall into their places the hypothesis grows stronger and stronger in probability, until, by a large accumulation of such corroborations, the hypothesis passes the undefined line which separates it from theory, and becomes a theory.

This theory then goes on increasing in strength by each additional fact which is found conformable to it, until its convincing force is almost as great to the mind as one of the facts which are the bricks of its construction.

But if, during this period of probation of an hypothesis or of a theory, a single fact is well authenticated which is inconsistent with it, the hypothesis or theory must be abandoned. Of course, in the case of a theory which had been tried and proven hundreds of times, and found to apply to newly-discovered facts, its abandonment would be held in abeyance until every effort had been made to prove the authenticity of the fact and its inconsistency with the supposed explanation; but if these were unalterably confirmed the hypothesis of theory must fall.

This constitutes the true principle of inductive philosophy, and only by pursuing this path rigorously can its processes lead to any good result.

(To be continued).

COTTON-BLEACHING WITH OXYGENATED

WATER.

By M. PRUD'HOMME.

THE addition of calcined magnesia to oxygenated water has been recommended for bleaching cotton, but the superiority of the results obtained has not received any explanation. It depends, as I am about to show, on the formation of magnesium peroxide, which at 100° is more stable than hydrogen peroxide.

1. Oxygenated water at 6 volumes, diluted with 10 parts of water, was boiled for half an hour; its standard fell

from 1000 to 100.

2. A similar quantity, with the addition of calcined

magnesia (5 per cent on the weight of the hydrogen peroxide), falls in strength only to goo.

3. Calcined magnesia is placed in contact with oxygenated water at 3 volumes, at the ordinary temperature. The duration of the contact varies from some hours to many days. It is filtered, washed on the filter, and the product dried at from 100° to 105°.

The determination of the active oxygen by means of a normal solution of potassium permanganate corresponds to the formula 3Mg(OH)2+ MgO(OH)2. This body, by an alkaline reaction, loses all its active oxygen at about 300°.

Magnesium peroxide is also formed on dissolving the metal in oxygenated water. Weltzein considers the product of the reaction a soluble magnesium hydrate. It is easy to show that when evaporated to dryness it gives, with the ordinary tests, the well-known reactions of oxygenated water.

The oxides of zinc and cadmium (metals belonging to the same series as magnesium in Mendeleeff's classification) also give rise to peroxides. The mixture of zinc oxide and peroxide corresponds approximately to the formula 2ZnO+ZnO(OH)2 Cotton bleaching with oxygenated water would remain unintelligible if we confined ourselves to consider it as a simple decolourising agent. It has a direct action upon the different bodies which bleaching has to modify or to eliminate, and even upon cellulose.

Action upon Fatty Bodies.

The saponification of the oils or fats is effected in part by the magnesia, but it is also due to the direct action of the oxygenated water. During ebullition there takes place an abundant liberation of carbonic acid; it may be derived from the oxidation of the glycerin, as it is verified directly. But the oxygenated water, very faintly acid, attacks also the neutral fatty bodies at ebullition, with the liberation of carbonic acid and a formation of fatty acids. These again are transformed by the mixture of oxygenated water and of calcined magnesia, and always with the production of carbonic acid. This happens with the stearic and the oleic acids of commerce. There must occur a partial transformation of this latter body into palmitic acid (as if by the action of potassa lye), for the product of the reaction, if suitably treated with an acid, is richer in soluble fatty acids than the oleic acid of which it forms a part.

The fatty bodies which remain upon the fibre in the state of magnesium oleates, palmitates, &c., are elimi. nated by a passage in weak acid, followed by an alkaline lye.

Action upon Cellulose.

In bleaching with oxygenated water the cellulose tends to become converted into oxycellulose. This is easily recognised by dyeing in basic colouring matters which fix themselves without a mordant upon oxycellulose.

The modification of the cellulose is more strongly marked if it has been mercerised, i.e., saturated with concentrated caustic soda before treatment with oxygenated water. The disaggregation becomes complete, and the tissue becomes a pulp if we add caustic soda to the bath of oxygenated water until it marks 6 to 8° I'w.

The action of oxygenated water upon cellulose is much increased by the presence of certain bodies, such as metallic oxides, which serve merely as a vehicle or intermediate agent for active oxygen. A swatch of cloth mordanted with iron, chrome, or alumina, and boiled with oxygenated water or magnesia for one to two hours, is profoundly attacked at the parts covered by the mordants. It is well, therefore, to let a treatment with weak acid precede the bleaching with oxygenated water, to eliminate the salts or the metallic tissues from the tissue.

The action of oxygenated water and that of cuprammonium upon cellulose present great analogies.

It is easy to show that the ammoniacal solution of copper oxide is an oxidising agent, by allowing it to act upon a