Imatges de pàgina
PDF
EPUB

THE CHEMICAL NEWS.

VOL. V. No. 112.—January 25, 1862.

SCIENTIFIC AND ANALYTICAL

character, one word in favour of Mr. Horsley. I think

it probable that there may be butters which do dissolve CHEMISTRY.

in ether at 65°, in the proportion even of 20 grs. to zj.,

although I hold that he has not proved it, nor have I yet On the Adulteration of Butter with Animal Fats, met with such a sample. And the reason of my opinion by EDWARD BALLARD, M.D. Lond.. M.R.C.P.: is, that I have found butters which I have every reason Medical Officer of Health for Islington, and Parochiaí to believe pure (barring the salt and water which all Analyst under the Adulteration of Food Act.

shop butters contain) leaving different amounts of residue

when acted upon in my cylinder. I append the result [THIRD COMMUNICATION.]

of experiment in three of these, 20 grs being used with I FIND from my friend Mr. Horsley's last letter that I must | 3j. of ether and left in the water-bath at 65° for one recur to the question of the solubility of butter (pure hour:and adulterated) in ether. He very courteously gives 1. “Dorset" butter, sold at 1 s. 3d. per lb., melted me credit for “ meaning well," but I claim something with boiling water in a beaker formed a layer nearly more than this. I claim to be right. Nor can I endorse uniform, the cellulations being so fine as to require a his ultimatum. I think that there is yet more to be said lens to distinguish them, and breaking down when cold upon the subject, and this I propose partly to say in the and dried into a very fine mealiness, tasting only of present paper. It seems that it must partake also some butter, residue 3.3 grs, of the form and appearance of what of the form of a reply. And my reply is this :- that from pure butter. 1. In Mr. Horsley's first communication he writes : 2. “ Fresh" butter, sold at is. 5d. per lb., professedly "If a piece of this prepared butter be introduced “unadulterated," by the agent of a farmer in the into a wide-mouthed stoppered bottle and sur-country, melted with boiling water, presented in the rounded with ether at the temperature of 65° Faht., melted form, and when cold, the same physical characters it ought to entirely dissolve, forming a clear, lemon- as above ; i.e., those of pure butter, residue 1.8 grs, of coloured liquid." He now says that he dissolves same form and appearance. the butter in a phial " held in the warm hand for a Here there are two samples which leave residues, the minute or so." This is not dissolving it at 65°. That, one greater the other less than in the pure sample I when thus dissolved at a higher temperature, it should described in my last paper. The third sample stands still be held in solution at 65° is altogether a different alone. statement. That all his experiments were performed in a 3. Butter imperfectly churned, very soft and creamy, similar manner is a fact which, to my mind, vitiates them. obtained from a friend, who prepares it for his own table. 2. I must decline to bow to Mr. Horsley's criticism, When melted and cold, physical characters those of on the ground that in his first paper he mentions pure butter as described above, residue 5'7 grs. When no proportions of butter and ether, and, therefore, dry, bulky, loose, and honey-combed ; deeply fissured in ought not to blame me for using those which are several piaces, and not aggregated like other samples of incorrect in my trial of his test. Doubtless, if an excess pure butter into the typical form. The cow from whom of ether be used, or the temperature be sufficiently this butter was prepared was stall-fed, and the butter raised, the solution might, as he describes, be perfect. was white. Here there are all three grades of residue, But I also decline to submit to his criticism, because in It is possible to imagine butter with even less residue, the experiments he relates he uses the same “im- till it amounts to nil. But I say this has not yet been moderate" quantities that he accuses me of experiment- | fairly shown. ing on. If he reads my last paper, he will find experi. And now for another branch of the subject. I think ments where the proportion of 10 grs. to 3j. of ether it is Dr. Hassall who has somewhere suggested that the were those employed; still with a residue. 3. I assert consistence of butter at various temperatures may posthat these last described experiments of his are not sibly furnish a test of their adulteration with foreign fairly conducted, even allowing the question of tempera fats. It appeared to me that this suggestion was worth ture to stand aside. He did not use adulterated butter carrying out. But the consistence of a substance which where the ingredients had been fairly mixed by melting may present every degree between complete fluidity and together, but the butter and the adulterant separate from absolute hardness, passing through every stage of soft each other. This is no trifling error, especially when solidity, seemed at first so difficult to represent that for a lard was used ; inasmuch as the physical conditions of long time I despaired of a method of testing it. And the latter causes it, when unmixed with butter, to resist the difficulty was increased by the irregularity with the action of the ether. Again, the appeårance of the which caloric diffused through a hard niass of butter or deposit is no criterion of its absolute quantity; a loose fat exposed to increased temperature. It also occurred deposit, though bulky, may weigh wonderfully little, to me that possibly the a pearance of the butter, its and vice versa. I know by observation that this is so clearness and limpidity at different temperatures, might in the instance in hand.

tell us something; but here I found that the rapidity or And now, before passing to observations of a different slowness with which the heating was effected modified

[ocr errors][merged small][merged small]

the result, as did also every irregularity in the rate of 127 minutes and at 73° the readings through “clear" warming by introducing a disturbance either from con- | layer slightly obscured ; and in vection or gravitation. The only satisfactory mode of 145 minutes and at 71° the numbers on thermometer carrying on such an inquiry thus turned out to be by at in “ clear” layer illegible, and scarcely even visible. A once raising the substance to a high temperature and slight secondary gravitation apparent from the greater allowing it to cool slowly, gradually, and uniformly. obscurity of the markings through the upper than But then, how to measure and represent the consistency through the lower part of this layer. The stem of ther. I experimented thus :

mometer now gradually became lost to view, the opacity My apparatus consisted of a test tube, length 41 in.; proceeding from below upwards, so that after diameter, tin.; an ordinary chemical thermometer, 165 minutes and at 69° none of the stem of the therdiameter of containing tube, o in.; diameter of bulb, mometer was visible, the upper part of the “clear" 1 in.; length of bulb, i in.; and a half-pint beaker, to layer, however, remaining more translucent than the serve as a water bath. I used throughout the same tube, lower. The punctiform appearance of the opacity still thermometer, and beaker, so that the comparison of the remained. experiments might be fair and incontestible. The weight 178 minutes and at 68o. The loaded tube could be of the tube was 175 grains, and the quantity of butter, raised one inch out of the water, and then the thermo&c., acted on was in each instance the same, viz., 155 meter began to slip. In grains, making a total weight of 330 grains. Having 222 minutes and at 66° it could be raised completely weighed the butter, &c., in the tube, I pressed the ther-out of the water, but, after a few seconds of supporting, mometer to the very bottom of its centre and supported it began to slip. the whole upright in the beaker, which I filled to the On repeating this experiment the same results were brim with boiling water. I noted the point to which obtained, but the cooling was still further continued, the thermometer rose, and then allowed the whole to viz. for 505 minutes and to a temperature of 60°, at cool spontaneously, noting also the time it took to attain which the thermometer still slid out. It was now left various temperatures; and, lastly, I noted the time and for the night, and in the morning, at a temperature of temperatures at which various changes in appearance of 55° the loaded tube could be supported out of the water the liquid took place, and at which it had acquired and oscillated. sufficient solidity to enable me to raise the loaded tube Second Experiment.-BEEF DRIPPING-At by the thermometer, which now became fixed in the fat 170° was liquid and almost clear, presenting a very or butter, first an inch or so above the water in the trifling milkiness, the readings being clearly legible beaker, and next completely out of it, so as to allow of through it. By the lapse of its being oscillated without permitting the thermometer 25 minutes and at 120° the milkiness had assumed the to slip. I experimented upon pure butter,—the sample I form of very fine points. After mentioned in my last paper, -upon beef and mutton 60 minutes and at 90° these points had become more dripping, upon lard (home made), and finally on the distinct, but not flocculent, and at the upper part the several adulterated butters. I will endeavour to com- readings were slightly clearer than at the lower, showing press as much as possible the results of my experiments. a trifling gravitation. After

First Experiment.-PURE BUTTER—Carefully dried, 80 minutes and at 80° the opaque points were very raised to

distinct, and either larger or more numerous, for they 169o. Liquid, cloudy from minute points. Thermo- were so diffused throughout the liquid as to render the meter visible, but not the markings on it. After a few readings everywhere more obscure, but still legible. minutes the points became more distinct, and after After

20 minutes and at 122° they had aggregated into an 85 minutes and at 79° the numbers on the thermometer universally diffused fine flocculence, and the mercurial were illegible; the bulb and lower part of the stem were column had become visible. After

slightly more obscure than the rest. In 35 minutes, and at 108°, the first evidence of gravita- 88 minutes and at 78° the numbers and mercurial tion of the flocculi became apparent by the formation of column were invisible. In a line of clear fluid at the top, which now gradually | 96 minutes and at 76° the thermometer was wholly increased, until after

invisible. In 78 minutes, and at 82, the clear layer, through which 107 minutes and at 740 the loaded tube could be raised the numbers on the thermometer were quite legible, had a quarter of an inch out of the water. In attained the depth of half an inch (the entire of the 111 minutes and at 73° it could be raised nearly out of butter occupying about an inch and three-quarters); the the water; and after bulb had become now obscure by gravitation of the 115 minutes and at 71°it could be raised and supported flocculi, but both this and the lower part of the stem out of the water, and oscillated without slipping. were still visible through them. In

Third Experiment.-- MUTTON DRIPPING-At 110 minutes and at 75o the clear layer had attained 177° was liquid and colourless, presenting a very slight about one inch in depth, and the bulb, which at 76° was milkiness, apparently due to very fine points ; numbers still obscurely visible, was now quite lost in the deposit. on the thermometer were all very legible and distinct. This total obscurity of the bulb was synchronous with After a change in the clear layer (a change which occasioned 64 minutes and at 919 points had gradually become the total obscurity by filling in the interstices of the larger and more distinct; the readings were equally deposited flocculi), viz. the appearance of minute points legible, but rather less so at the lower than the upper in the clear top layer. In

part. In 118 minutes and at 74° no further gravitation of 71 minutes and at 88° points much larger, but 10 flocculi had occurred, but the points in "clear” layer flocculence; numbers less legible. In had become more distinct, and the deposit was to the 80 minutes and at 870 numbers illegible, but still eye denser and more opaque, obscuring totally all that visible. In part of the thermometer it surrounded. In

1 84 minutes and at 86° bulb and lower part of stem

[merged small][ocr errors][merged small][merged small]

lost to view, and within one minute the whole of the stance which corresponded with that forming the floccustem was invisible. At 85° the thermometer was not lent deposit in butter, but the solid material began to be yet fixed. In

deposited in points at a much higher temperature, viz. 95 minutes and at 84o the loaded tube could be sup- in mutton and beef dripping considerably above 90° and ported out of the water and oscillated without slipping. in lard about 88'. The difference is probably due less

Fourth Experiment.-LARD (home made)—At to the difference in the melting point of stearine and

1682 liquid and as clear as water, and thus without margarine than to the amount of the liquid elements in any remarkable change it continued for about an hour. these several fats. 8. The time occupied in acquiring After

the same degree of solidity was for these four fats least 59 minutes and at 88° a diminution of clearness became in mutton fat and longest by far in butter, lard occupying evident. After

a shorter time than beef fat. 9. Lard presents in the 66 minutes and at 850 obscurity had increased, rium act of solidifying a remarkable rise in temperaturebers everywhere still legible, but less distinctly at lower about 83°. I found a similar phenomenon occur with a than at upper part, and bulb not quite so distinctly sample of lard which was purchased. visible as the stem. After

Isiington Parochial Laboratory, January 1, 1862. 68 minutes and at 841° numbers everywhere illegible. After 71 minutes and at 84° numbers and mercurial column

On the Estimation of Sulphur in Iron and Copper only obscurely visible. Opacity distinctly punctiform. In

Pyrites, by M. J. PELOUZE. 75 minutes and at 83° stem of thermometer only SULPHURIC Acid has of late years been almost excluobscurely visible.

sively manufactured of Sicilian sulphur. The quantities And now occurred a remarkable phenomenon which exported from this island are truly immense, for France did not occur with butter, or beef, or mutton dripping, alone imports not less than thirty millions of kiloand which was apparently due to rapid solidification. grammes. The temperature fell about a quarter of a degree, and At the present time sulphur is being replaced by iron then began to rise until it reached 838°. Thus, after pyrites or by ferruginous pyrites, more or less rich in

82 minutes and at 83*° the temperature became sulphide of copper. This latter kind of pyrites is chiefly stationary for a minute or two, and then began again to obtained from the shores of Spain, whence it is exported fall. During this time the stem of the thermometer was to England. It serves at the same time for the manuquite invisible from opacity and solidity of mass. It facture of sulphuric acid and for the extraction of copper. attained after

France possesses several deposits of pyrites. The 86 minutes 83° again. After

factories of Paris, Lille, Chauny, Rouen, &c., are prin94 minutes and at 81° the loaded tube could be raised | cipally supplied from Chessy and Sain-Bel, near Lyons, in the water, but the thermometer was not yet solidly Those of the south obtain their pyrites from the neighfixed. After

| bourhood of Alais, and other factories derive it from 104 minutes and at 79. it could be supported out of Belgium and Rhenish Prussia. the water, and oscillated without slipping.

It will readily be imagined that several sources are The differences in the phenomena of cooling of these necessary for a substance the annual demand for which four substances may be summed up as follows:-1. The approaches 100,000 tons. formation of flocculi in the cooling liquid is a peculiarity The composition of these pyrites being extremely distinctive of butter. In the sample described the first variable, the mercantile transactions connected with opacity observed was in points. În another sample of them are necessarily based on the amount of sulphur pure butter-that which gave 1.8 grains residue with they contain, and it is requisite to determine it frequently ether--mentioned in an earlier part of this paper, the and with care. On the other hand, it is not requisite flocculi were visible from the first, viz, at 1719 2. for the manufacturer to know the quantity of sulphur Butter at all temperatures above 55° is less solid and left in the residue after roasting the pyrites. He should consistent than beef or mutton dripping or lard. It is endeavour to exhaust these residues as much as possible, still quite liquid when mutton fat and lard have solidi for hitherto the roasted pyrites has not been usefully fied, and is only on the eve of solidifying when beef fat employed. It has been recently sought to be utilised is solid. 3. The order of solidification of the four fats for the manufacture of cast iron of an inferior quality, on cooling is mutton, lard, beef, butter. 4. Butter is but appears to have been given up. This is easily quite solid only at a temperature of about 55° (in an explained when it is remembered that the unburnt experiment with the other sample of butter mentioned sulphur which remains mixed with the oxide of iron above it was solid at 599). Perhaps it may be said that amounts to 3, 4, and 6 per cent., and sometimes to a its solidifying point is at least from 12 to 16 degrees more considerable amount. below that of beef dripping. 5. This difference is In the present state of things, analyses of metallic observable throughout the cooling. Thus complete sulphides are in general performed with accuracy, but opacity was observed in the mutton dripping at 84, in unfortunately with extreme slowness. They are treated lard at 83° or thereabouts, in beef dripping at 76, and with aqua regia, the solution diluted with water filtered, in butter at 699 6. There exist in butter two snb and the sulphuric acid precipitated by a baryta salt. stances at least which are insolubl o lein a i nm Le weight of the sulphate of baryta the proporother conjoined liquid elements

r. Vongo sulphur may be calculated. This method requires, these is insoluble at temperature bo

the methods of analysis by the wet way, a certain highest temperature I have

It je

her.cal manipulations. this which forms the RTID.

4 manufacturers of sulphuric acid are insoluble only below 249

tlg for a simpler and more rapid process. the points during sblici in

To propose cannot fail to como 7. In mutton fat, beef far

e nothing else but an alkali

[graphic]
[graphic]
[ocr errors]

On the Estimation of Sulphur in Iron and Copper Pyrites. {Chanca, 18%.

metrical assay-of all industrial processes the one with crucible itself. I throw it on a filter and wash it again out exception best known and practised.

with boiling water. That will be understood when it is remembered that A little experience soon enables one to effect com. the manufacture of salts of soda is so bound up with the pletely, and without any loss, the thorough washing of manufacture of sulphuric acid that a soda furnace is the substance operated upon. The solution and the never seen in a factory without at the same time the washing waters are lastly neutralised with the normal leaden chambers being met with.

sulphuric acid, without any modification of the method My new process is based upon the property which and precautions recommended by Gay Lussac. chlorate of potash possesses in the presence of an Supposing that it has been found necessary to employ alkaline carbonate of transforming into sulphuric acid 34 cubic centimètres of normal acid ; subtract this from the sulphur contained in metallic sulphides, especially 46.2 cubic centimètres, and there will remain, therefore, those of iron and copper, the only ones employed in the 12'2 cubic centimètres, which represents the sulphuric manufacture of sulphuric acid. This re-action, if well acid formed by the pyrites. This number multiplied by managed, is complete; that is to say, the whole of the 32.653, and divided by 100, gives the weight of the sulphur passes into the state of sulphuric acid. This sulphur sought,-'0398, or 39.8 per cent. unites with soda or potash, or with both these bases at A quartzose, barytic, or calcarious gangue does not in once, which is immaterial when regarded from a purely the least interfere with this process. analytical point of view.

The residue, after washing, should dissolve in hydroIt is necessary to employ more carbonate of soda than chloric acid without deposition of sulphur. It is easy to is pointed out by theory, so as to avoid losing sulphuric ascertain this, for, in a badly-managed assay, the sulphur acid. This excess of carbonate of soda is easily esti- separates from the gangue in the form of light flocks, mated by the ordinary alkalimetrical means.

| recognisable by the blue flame and by the odour of The neutralisation of the carbonate of soda is there- sulphurous acid which they give when burning. When foie performed twice, first by the sulphuric acid formed this happens, which is very rare, and indicates generally at the expense of the sulphur during the calcination of a badly-incorporated mixture, the analysis should be the above-named mixture, and secondly by dilute sul recommenced. phuric acid of any known standard.

I am satisfied (and this is an essential point) that Normal sulphuric acid being met with in laboratories, there is no disengagement of sulphurous acid during I employ this in preference to any other acid solution, the combustion of the perites by receiving the gas This is of such a strength that 10 grammes of pure and either in a warm solution of aqua regia, containing a dry carbonate of soda are exactly neutralised by 92'4 small quantity of chloride of barium, or, which is still cubic centimètres of normal acid. These numbers corre- better, in a solution of permanganate of potash. I have spond to equal equivalents of carbonate of soda and of detected neither the precipitate nor the decolouration, monohydrated sulphuric acid. A litre of normal acid which are characteristic of sulphurous acid. contains 100 grammes of monohydrated acid, or 32*653 I have made some other experiments to ascertain the of sulphur.

accuracy of my process; they are the following: Suppose, now, that in an analysis of pyrites I have

I. Specimens of pyrites in cubes of the most perfect employed five grammes of carbonate of soda. I know

sharpness, for which I am indebted to the kindness of that it would have required 46'2 cubic centimètres of

M. Combes, yielded me in six analyses quantities of normal acid to neutralise it directly ; but if after the combustion of one gramme of pyrites, for example, I

sulphur comprised in each case between 53 and 54 per only require 30*2 cubic centimètres of acid, that shows

cent. The formula FeS, contains 53*3 per cent. that there has been formed by the oxidation of the

II. Specimens of natural and roasted pyrites from the sulphur an amount of sulphuric acid precisely equal to manufactories of Channy have been analysed both in that contained in 16 cubic centimètres of normal acid

the laboratory of the factory and in my own, by the for 16 cubic centimètres and 30:2 cubic centimètres make aqua regia and baryta method, and also by my new together 46'2 cubic centimètres. There only remains, pro therefore, to calculate how much sulphur there is in 16

I These substances have furnished, by this double cubic centimètres of normal acid. I obtain this by the

treatment, quantities of sulphur which in no case following proportion :

differed from each other more than it per cent., and

which generally corresponded. 1000 C. C. : 32.653 :: 16 c. c. : x=0:522 of sulphuri

III. The product of the calcination of the mixture Thus I gramme of such a pyrites contains 0'522 of above named, well extracted with water and saturated sulphur, or 52'2 per cent.

with hydrochloric acid, gave with baryta the sanie I now pass on to the description of my process. I weight of sulphate of baryta as by the ordinary agua will suppose that the analysis of an iron pyrites is to regia process. be performed.

I have also found similar results with several specie I accurately mix, in a porcelain mortar, i gramme of mens of copper pyrites. porplıyrised pyrites, 5 grammes of pure and dry car- ! I have not hitherto mentioned any but iron and copper bonate of soda, 7 grammes of chlorate of potash, and 7 pyrites. I will now explain, in a few words, the appligrammes of fused or decrepitated marine salt. Ication of my process to roasted pyrites in which the introduce this mixture into a platinum crucible, and makers of sulphuric acid have so much interest in gradually expose it for eight or ten minutes to a dull knowing the amount of sulphur, and of which they are red heat; the marine salt is added to prevent too violent constantly obliged to analyse a great number of an action.

specimens. When the mixture is nearly cold I add warm distilled in this case I dispenso with, as useless, the employ. water to it, and remove the solution by means of a ment of marine salt. I mix accurately five grammes of pipette, and filter it. I repeat the washing five or six roasted pyrites, five grammes of pure and dry carbonate times, and finally boil the residue with water in the of soda, and five grammes of chlorate of potash.

CHEMICAL News,
Jan. 25, 1862.
Royal Institution of Great Britain.

47 I expose the mixture to a dull red heat in a platinum crucible. The oxidation of the sulphur takes place

PROCEEDINGS OF SOCIETIES. slowly and without any deflagration. The rest of the experiment does not differ from that pointed out for iron ROYAL INSTITUTION OF GREAT BRITAIN. and copper pyrites. If it has required 40 cubic centiinètres of acid to neutralise it, it shows that the 5 grammes of roasted pyrites contained 0'202 grammes of

A Course of Six Lectures on Light' (adapted to a Juvenile sulphur, or 0.0404 for 1 gramme, or 4 04 per cent.

Auditory), by John TYNDALL, Esq., F.R.S., Professor of When the roasting has been badly performed, it is not

Natural Philosophy in the Royal Institution. uncommon to find pieces of pyrites still containing from

LECTURE III. (Dec. 31, 1861.) 12 to 15 per cent, of sulphur; in these cases the above

NOTES TO THE LECTURE :named proportions of carbonate of soda and chlorate of When a ray of light passes from a rarer to a denser medium it is potash must be increased,

bent towards the perpendicular-When it passes from a denser to a

rarer medium it is bent from the perpendicular-But the density or In conclusion, I must urge the necessity of washing

rarity here meant is not that which is expressed by the weight of a with boiling water, which is a matter of no difficulty; body. A body may be optically denser than another, though it be the washing in the cold is long, and generally insufficient.

lighter of the two-Spirit of turpentine floats on water, and is there.

fore lighter, or, in ordinary language, less denso than water ; but a The reason is, undoubtedly, that with pyrites having a ray of light, in passing from turpentine to water, is bent from the

perpendicular, and in passing from water to turpentine it is bent

towards the perpendicular-In optics the densest body is that which alkaline silicate which only dissolves easily in warm refracts most.. water.

Conceive a ray of light passing from a denser medium to a rarer,

striking the common surface of both so obliquely, that on quitting I will add, that any loss of carbonate of soda occasions ihn dansen

the denser medium it is refracted so as just to graze the surface-The an apparent increase of sulphur; this is evident, since angle between that ray and the perpendicular is called the limiting the amount of sulphur is judged from the volume of

angle, and for this reasou-Becaure no ray that strikes the surface at

a larger angle than the limiting angle can get out of the denser normal acid employed to complete the saturation. The medium. All such rays as striking the surface are totally reflected, carbonate of soda lost will wrongly be supposed to have

a cording to the law mentioned in the notes of Lecture I.-The limit.

ing angle then marks the limits of possible transmission from a denser passed into the state of sulphate, and the calculation of the

to a rarer me lium. This is the only case in which the reflection of proportion of sulphur will be established on a false basis. Jight is total- A liqnid vein may be filled wi b light which cannot It is, however, easy, with a little care, to avoid errors of

escape from the vein in consequence of total reflection- Mirage is pro

duce I by the total reflection of rays passing obliquely int, the rare air this sort, and also of others which I will now mention. | close to the hot surface of the earth. Trees and houses may be seen I need scarcely say that the carbonate of soda should

thus reflected from the air as if from water.

The human eye is composed of three principal optical parts; the

aqueous humour, the crystalline lens, and the vitreous humourwith as much accuracy as the pyrites itself. This care Behind the vitreous humour is the retina, which forms a screen to

receive the images of external objects produced by the eye; these is not necessary in the case of the chlorate of potash and

images are always inrerted-For distinct vision it is necessary that the chloride of sodium. The proportion of the latter salt rays from every point of an object should come to a focus upon the may be varied according to the combustibility of the retina-Some eyes refract too much and bring the rays to a focus too

soun: to remedy this defect a divergent lens is placed before the eye; pyrites, and must be increased until the oxidation of the

this is short sight-Some eyes do not refract enough, and to help mixture takes place without deflagration. Finally, the them we place a convergent lens before the eye; this is long sight

Divergence is promoted by bringing the object close to the eye; ccnmost necessary precaution of all consists in very finely

vergence is assisted by holding the object far from the eye; hence the powdering the pyrites, and mixing the whole very inti terms 'shrt sight" and "long sight.”

The action of light upon the eye does not subside the moment the mately together.

light ceases; the impression endures in some cases nearly a quarter of To sum up, the new method of analysing the metallic a second after the light has ceased to shine-A succession of sparks, sulphides consists in the combustion of the sulphur by therefore, which follow each other at intervals of a quarter of a second,

would appear as a continuous light; in fact, each impression would means of chlorate of potash in the presence of carbonate

arrive before the preceding one had disappeared-To tie eye a lumiof soda. The sulphur passes entirely to the state of nous object appears larger than it really is, and the more intense its

light, the larger does the object appear. This effect is called irradiasulphuric acid, which neutralises a portion of the alkaline

tion-The full moon appeare larger wben lookei at with the naked carbonate. The excess of this salt is ascertained by the eye than when looked at through a dark glass. The bright new moon

appears to belong to a larger sphere than the dusky globe which it

partially encircles. the saturation ; this volume is subtracted from that

The white light of the sun is made up of an infinite number of rays of different retrangibilities-Each particular refrangibility corresponds

to a particular colour; hence the number of colours involved in solar carbonate of soda to directly neutralise it, and the dif

light is inanite-But for convenience sake we divide these colours

into seven, which are called primary colours. These are red, orange, the pyrites. From the amount of sulphuric acid that of

yellow, green, blue, indigo, violet-Of these colours the red is the

least refrangible, and the violet the most refrangible; the other the sulphur may be obtained by calculation.

colours being intermediate between these two-The solar beam is reThe process does not occupy more than thirty or forty solved into these colours by passing it through a prism; the coloured

image thus formed is called the solar spectrum-The colours of the minutes; the errors involved in it do not exceed 1 to

spectrum, when suitably blended, produce white light. 1} per cent. of the weight of the sulphur to be determined. Ann. de Chim. et de Phys., Third Series,

I have now to say two or three words in completion of Vol. lxiii.

the memoranda of the last lecture. I have said there that "If two bodies refract a ray of light equally, one of them

cannot be seen within the other." Now let me say (ne Royal Institution.-On Tuesday, January 21,

or two words upon the refraction and reflection of light in in the afternoon, John Marshall, Esq., delivered a lecture

ed a lecture completion of what I have already mentioned. I have or "The Physiology of the Senses." On Thursday, January

day, January here a large piece of glass with parallel polished surfaces; if 29, in the afternoon, Professor Tyndall delivered a lecture

| a beam of light falls upon that glass you know that a portion on " Heat." Last evening Professor Rolleston delivered a

| of it is reflected, making the angle of incidence equal to lecture on “The Affinities and Differences between the

the angle of

portior/ eve, goes through, Brain of Man and the Brains of certain Animals."

and may tie

the other t er having passed On Saturday (this dry) January 25, the Rev. A. J. D'Orsey through the IALA " the first sur. will deliver à lecture on “ The English Language," at three o'clock.

[graphic]
[ocr errors]
« AnteriorContinua »