THOUGHTS OF A NOTED SCIENTIST.

Otago Witness, Issue 1915, 3 August 1888, Page 32

THOUGHTS OF A NOTED SCIENTIST.

fl/HAT PROFESSOR PKOCTOR HAS TO SAY ON A VARIETY OF SUBJECTS.

[The sole right of publication of this inte resting series of articles in New Zealand has been secured by the proprietors of the Otago Witness.]

No. 111, — CHEAP CHEMICAL EXPERIMENTS FOR AMATEURS.

Colour Changes on Chemical Mixture— Two Liquids Mix into a Solid — Two Solids Mix into a Liquid — Useful Chemical Experiments — Natural Bleaching — Artificial Bleaching— Kemoving Ink StainsDestroying Written Eecords— Why Printed Records;, will Not "Yield -Experiments by Mxing Various Chemicals with the Chemicals Inside the Body-Choice of Time— What Before a Meal has One Effect, May After a Meal have ithe Contrary Effect -Chemical Experiments with the Body not Always Cheap-

(Copyright 1888 by the Author.)

Probably none of the mudern sciences, unless it be astronomy, has been in its infancy more closely connected with superstition than chemistry. The wonders which in past ages passed for miracles were nearly all chemical, a few only byiug mechanical and other few being optical. As {Sir David Brewster said in his celebrated letters on natural magic, " chemistry has from its iufancy beiug pre-eminently the science of wonders; in bis laboratory the alchemist aud magician have revelled uncontrolled " (whatever that may imply), " and from her treasures was forged the sceptre which was so long and. so fatally wielded over human reason." We have only to read the records of ancient delusions, as described be it remembered by persons unacquainted with tbe r^al interpretation, to see how large a part chemistry played iv the performance, though the seeming miracles were then and have bron since iv »orao cases attributed somewhat profanely to Deicy.

As chemibtry lent itself freely to the devices by which iv old times the people were deluded, so'nqw it ia of all sciences that by which the sense of wonder may be most readily oxcited, and this by devices which are often exceedingly simple. The modern magician does not indeed invoke superior powers to bring about change* which he kuows to be at hand ad a resulc of his owu preparations. He may even assume no moreimpressive a form than that of the grave and explanatory lecturer, who not only announces' the nature of each experiment aud explains all that takes place, but considers that he has failed of his purpose if his explanations are not understood and the sense ot wonder remains unconnected. Amoug

Simple Experiments which can be readily and cheaply exhibited the following may be mentioned, which require only readily procurable ingredients and materials : — Pour into one glass a small quantity of a solution of nitrate of bismuth, and into another a small quantity of a solution of prussiate of potasbium. These two liquids are both colourless. But on pouring them together a liquid showing a fine yellow colour is produced. The chemical interchange which takes place produces prussiate of bismuth aud nitrate of potassium, in place of nitrate of bismuth and prussiate of potassium. The prussiate of bismuth gives the yellow colour. In like manner a mixture of a few drops of the colourless prussiate of potassium, with a small quantity of an equally colourless solution of the sulphate of iron, produces a liquid which has a beautiful blue tint, itself more than sufficient to reward the experiments by its loveliness for the slight trouble and expense which the experiment involves. (I must admit that the beautiful colours and forms which are obtained in many chemical experiments have a greater charm for me than even the scientific principle which such experiments illustrate ; and, somewhat strangely, I find the artistic pleasure I derive from colour experiments increase with advancing years.) The blue colour obtaiued in this experiment is the familiar Prussian, blue of our paiut boxes. The decomposition which takes place is bitnple. Sulphuric acid leaves the iron to combine with the potassium, the pntiissiuiu leaving the iron to combine with the prussic acv 1 . A litile of toe solution of sulphate of copper mixed wuh the pnisMata of potassium of the last experiment, pio mces u reddish brown liquid, not, particularly attractive in colour, the chroncal'h eoropo.-U'iuu giving sulphate ot potassium and prushiate of copper.

Tb« form itiun of a black liquid from t.wo colourless liquids is interesting as beiug tho process by which the old ink of commercti was formed. A small qu.iutiifcy of gallic tincture is lo lie added to \w\ter, and to the colourless liquid thus obtained is to b« added a small quantity of the sulphate of iron. The mixture b come* black. (The gallic acid unites with the iron in this experiment.) I may remark here iv passing that though the oldrfflshioued gallic ink had its faults, it was in my opiuion altogether superior to the

'» WiUd Writing ink " now in such common use. I know of no ink ever iuvouted more undesirable than this laat. It has great fluidity, be it grauted j and this js doubtless a desirable quality. It also illustrates admirably several chemical principles, but they ar« not such as we de6ire to see illustrated when writing. For example, it corrodes the metallic pen we are using ; but it is not pleasant when, perhaps after loug searching, on« has found a pen which writes with absolute smoochness and neatness, to have that pen presently spoiled, ev;n though the process by whiuh the metal of peu enters iuto chemical eornhiuatiou with the acid of the ink b*: scieutittcally interesting. (I am myself, like most rapid writere, rather hard to please in the matter of pens). Again the fluid ink writes light, though the writing presently turns dark, owing to a chemical change of considerable interest; but every library man likes hi* writing to be dark from thu start. An even woi>« fault of this truly hateful writing fluid is that if you pause to ihiA, a process considered ocrca-ionally allowable eveu among literary men, bur- which i.b« inventor of fluid ink evidently railed to take into account, the chemical process oy which your peu is being destroyed takca place so t fleotively as to transform, the green fluid ab.surdiy called ink iuto a sickly yellow, which does not turn bla.<:k ai'tor writing. You are obliged to take a fcebh supply of the fluid on your nil>, if you would not have several words ot your writing of tho colour which dur Irish frienis poetically term "dunducketty mud colour " (To be scientifically accurate you ought to dry the pen before tak'tug this fresh

supply). Again the fluid ink is so undesirably fluid that manuscript written with it is bouud to be plentifully smeared, for the ink is ready to smear long after any reasonable ink would be dry. The fluid ink seems to have been invented solely in the interests of the makers of 'steel pens ; for while, in the first place, it cannot be used with quill pens, since the chemical changes' on which its' ultimate blackness depends require the iron of the pen, it so rapidly destroys steel pens .that one must use at least three times as many as one would require with good ink.

I may note hero that tho old-fashioned ink could be used to produce the best dead black colour which I know of. (The discovery is original with me, so far as I know). You take black French chalk — the usual crayon chalk— and score over with it the surface you wish to blacken, paying no special attention to uniformity, and leaving all tha chalk dust on the shjeet. Theu with a briishfui of the old-fashioned gallic ink, '(or you may use a feather) you go over ithe surface thus roughly blackened, aud forthwith find that a beautifully uniform black is produced, which on drying is a fit surface foe drawing on with coloured or white chalk. It is especially desirable for pictures of nebulaj, comets, and other such objects.

We are led to consider at this point the importance of ink for written records, aud the absolute necessity, if such records are to be safe, of the quality of resisting all buch chemical processes as reverse the changes considered above, turning coloured into colourless matter. It is well known that the old-fashioned ink yields to several chemical agents. If ad vantage were only taken of this to remove ink stains where ink st<ius are not desirable, this would be a gain rather than a defect. But records of various kinds may be treated with chemicals till the ink disappears — with results altogether undesirable. A solution of oxalic acid, or of hydrochloric arid, will act as an effectual bleacher in the case of all ordinary inks, the acid of the solution euteriDg into combination with the metallic colouring material of the ink, leaving one colourless liquid and producing another. If the ink- marks thus removed be records relating to property, signatures to deeds, the filling-in of cheques, or the like, the results of such chemical experiments are by no means such that the persons chiefly interested in them can regard them as cheap. They will, however, continue to be performed until or unless the inks used for such purposes be absolutely iudelible.

Now, it will probably have been noticed by many that printed matter is not affected at all by the agents which remove ink stains. Tho reason of course is that the ink used by printers owes its blackness to lampblack, which is almost pure carbon, carbon being of all elemei ts the one which most stubbornly resists the attacks of t'ue agents usually most effective-in producing chemical change. We recognise here the truo principles on which ink for written records should be prepared. The base should be carbonaceous, such other substances only being combined with the carbon as will give it a hold on the paper, without which, of course, the ink might be simply washed off. This hold on the paper should be such in some cases (as for cheques, &c.,) that the written matter cannot be removed by any mechanical means without destroying the paper itself. I fiud among the kosmun inks the requirements of indelibility, aud suitable hold on the paper, to prevent mechanical removal admirably provided for ; and from experiments I have made on this ink I infer that it is essentially a carbon ink. , Bleaching, or the Removal of Colour, is an interesting chemical process, whether natural or artificial, and in either form presents some of tho cheapest chemical experiments. Natural bleaching as it goes on in bleaching fields was formerly supposed to be the work of the sun's rays, but it is now recognised as th« work of the ozone in thft air. In town districts where little or no ozone exists in the air, cloth caimoii be properly bleached. If; is also known that ozone — which is an. allotropic form of oxygen — possesses powerful bleachingproperties, as tested in the laboratory. H«nce it may be assumed, as now generally by chemists, that the natural bleaching which takes place in couutry districts when cloth is moistened and exposed to the air, is effected by the ozone. Artificial bleachiug is chiefly done by means of chloride of lime, known as bleaching powder. The chlorine of this material destroys colour by uniting with the hydrogen of the colouring principle ; and when used in this way the chlorine does not unite with the Irydrogen of the fibre, and so destroy the substance of the cloth. Among Chemical Experiments of the Most Stri '. Ing Nature

those in which solids unite to form liquids or liquids to form solids are especially interesting. If equal parts of sulphate of sodium and acetate of lead, in the form of fine powder, be mixed together, and thoroughly pounded in a mortar, the two solids by their mutual chemical interaction will be resolved into a liquid. Again if muriate of calcium and a saturated solution of carbonate of potash be mixed together these two transparent liquids combine to form sulphate of lime, an opaque aud almost solid substanctt. If a little nitric acid be added to tbe mixture it is changed iuto a transparent liquid. If sulphuric acid is added, drop by drop, lo a concentrated solution of silicate of potash, and tho two liquids are stirred together with a glass rod, they are converted into au opaque white mass partially solid.

The study of chemistry, even in the form of such simple experiments as thesf, is especially valuable as illustrating processes which take place within our own bodies, iv digestion, iv respiration, and in the circulation of the blood It is desirable ev«n when we are in heakh to have some idea of tbe physical nature of such processes, for an intelligent concepticn of such matters suggest 3 tho importance of attention to diet, exercise, cleanliness, aud so forth. Many of the simplest details of our daily life involve important cbemical principles, the recognition of which eucouragts careful regimen and attention to many matters which are apt to be neglected. Among the txperiments we are oonstantly makiug ar« those which depend on the interactions of. various forms of food, solid and liquid, with the various* fluids produced within the body,' these fluids being thcnw;lv«3 the products of cbemicai combinations and chaMgiM (not within our control, or but very slightly).

It is well to conduct such experiments on sound facientitie principles, if we pay attention to them at all, and though too earnest an attention to the interior economy of our bodies is not altogether desirnble, yet men of seDse should see the propriety of knowing, in these days when the conditions of life are in fcuch a larj{* d<»jjrei' artificial, the natural effects of even si eh processes p,s eating and drinking, taking exercise in varior.3 ways, change of climate, &<\ Then agaia th* 1 pffects of surrounding conditions uavu often to be considered in their scientific a^peofc. Many important physical, and especially many chemical problem?, are involved iv the choice of a home, in the various details of house building and furnishing, even in such matters as the arrangement of the grounds round a residence. Sodding a space round a house may prevent poisonous exhalations from leaving the soil, the explanation of this effect

being almost purely chemical : and on the other hand ploughing a few fields near a home, or even a lawn, may lead to decided deterioration of the conditions on which the health of its inmates depends, and here again the recognition of the cause of the change requires a knowledge of physical as well as physiological principles.

It need hardly be said that where the body ia being treated with medicines of various sorts, important chemical experiments are in progress, which ib is better for many reasons to understand. Of course, for most persons under a course of medical treatment, implicit obedience to tho instructious of the doctor is proper and necessary. But oven so it is better to know why such obedience is desirable.

/ Ignorance of Chemical Principles more often leads to neglect of the doctor's injunctions than would the opposite fault of too clear an. idea of his plan and purpose; though I know many doctors entertain strong objections against giving any explanation n of thfrir prescript dons or any reasons tor adopting them. By this they avoid snch unwise intorfm nee with their plans as might be suggested to some among their , more inquisitive. patient?. But on the other hand ill-inforrad patients are apt to neglect details wh"J6h they mistakenly regard as unimportant. A doctor, for instance, tells a patient to take some medicine half an hour aft«r meals, and perhaps for a few days the patient attends to the injunction. But after a while he becomes careless, and from time to time allows tho proper time to pass, and not knowing any reason for supposing that the injunction as to time is important, he takes the medicine before meals instead of after. A little knowledge of chemistry would show him that the change instead of being a matter of no moment may entirely alter or even reverse the effect of the medicine.

Suppose for example that a patient is advised to take soon after each meal a dose of citrate of lithium. A dose so taken reaches the stomach at a time when the gastric juices are at work upon the material of the meal, and chemical chauges take place, ihe tendency of which is to correct acidity &rA in particular the development of lithic acid later on during the digestive process. Continuing this systematically, under medical advice, the pati«nt may protect himself against gout, rheumatism, and other ailments resulting from what is called the lithic diathesis. But, now suppose that the patient, unacquainted with chemical laws or with tho physiology of digestion, concludes that it is a matter of indiffe- ' reuce when he takes the medicine, and as more convenient to himself, elects to take it shortly •before instead of shortly after meals. In this case ihe citrate of lithium reaches the stomach when the gastric juices are not at work, and the chemical changes taking place are the reverse of those which aro necessary to correct the constitutional tendences of the patient. His constitutional ailments are exacerbated if actually in progress, or renewed if they have been remedied by previous more careful felftreatment.

Chemical experiments with the body, though cheap where they belong either to scientifically conducted regimen or to judicious control of the body by medical appliances, are apt to be very dear indeed where there is insufficient knowledge. Chemical reactions which are very interesting when watched in a laboratory may produce intense discomfort, danger, or even death, when they proceed within the experimenter's body. A little knowledge is here a dangerous thing, unless the learner is content to recognise the limits of his knowledge and to regard such knowledge as indicating the necessity either for further study or for obedience to the sugggehtions and injunctions of those who know more.

Richabd A. Proctoh.