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CHEMICAL NEWS,}

Dec. 15, 1876.

Repulsion Resulting from Radiation.

THE CHEMICAL NEWS.

VOL. XXXIV. No. 890.

ON REPULSION RESULTING FROM

RADIATION.-PART II.*

By WILLIAM CROOKES, F.R.S., &c.
(Continued from p. 242).

Iro. An examination of this Table shows that the action is by no means confined to the rays usually called heat, i.c., to the extreme- and ultra-red of the spectrum. The strong action obtained when the light is filtered through greenish glass and alum, or through ammonio-sulphate of copper, shows that luminous rays produce a similar movement of repulsion.

Unfavourable weather has prevented me from obtaining good quantitative results with the different rays of the solar spectrum; but I have tried numerous qualitative experiments which leave no doubt on my mind that any ray, from the invisible ultra-red to the invisible ultra-violet, will produce repulsion in a vacuum. The following is an experiment tried with the electric light. The spectrum was formed with a complete quartz train, no glass whatever being in the path of the rays. The purity of the spectrum was evidenced by the fact of the lines being sharp when thallium, sodium, or lithium was put between the carbon poles. The spectrum was so arranged that any desired ray could be thrown on to a lampblacked pith surface, screens being interposed to cut off the action when desired. The torsion balance was similar to the one used in the last-named series of experiments (104), but was not quite so sensitive.

The extreme red rays were first brought into position. On removing the screen the luminous index moved 9 divisions on the scale. The screen being replaced, the index returned to zero. A solution of iodine in disulphide of carbon was now interposed, and the screen again removed. The repulsion was almost as strong as before, showing that this liquid was transparent to the ultra-red rays.

The iodine solution was then replaced by a clear plate of alum 5 millims. thick, and the screen removed; a very slight movement only took place. The iodine solution was then put in front of the alum plate, so as to subject the extreme red rays to a double process of sifting. No trace of action could be detected.

Whilst this double screen was in front of the pith disk, the spectrum was gradually passed along, so as to bring the rays, one after the other, into position. No effect, however, was produced, showing that alum and iodine solution practically obliterate the whole of the spectrum.

The alum plate and iodine cell were now removed, and the green of the spectrum (the thallium line) was brought into position. The luminous index moved 6 divisions. The plate of alum cut off only a small amount of this action, but the iodine cell brought the index to zero. This is a proof that the action in this case was not due to the heat-rays of the spectrum, for these are practically transmitted by iodine, and cut off by alum.

|

The indigo-rays were next brought into position. The spot of light moved 3 divisions on the graduated scale. Alum cut off only a very little of the action; but the iodine cell was completely opaque to the rays, and brought the index to zero.

Finally, the invisible ultra-violet rays of the spectrum were brought into position. The train being of quartz these were abundant. Care was taken to keep any of the

253

luminous rays away from the pith disk. I think I succeeded in this; but it was not easy, owing to the fluores

cence of the card and other surfaces,on which stray rays fell. The spot of light moved 2 divisions, which were increased to 5 when the invisible rays were further concentrated by a quartz lens. The interposition of the iodine cell cut off the whole of the action. The alum plate cut off about half of the action, but scarcely more than would have been cut off had a piece of colourless glass of the same thickness been interposed, and it must be remembered that the alum plate has glass and Canada balsam on each side.

* A Paper communicated to the Royal Society, March 20, 1875. From the Philosophical Transactions ofthe Royal Society o London, vol clxv., pt. 2.

III. A similar experiment with the solar spectrum gave the following deflections, glass prisms being used:

Although I give the number of divisions shown by the luminous index, I attach little importance to them as quantitative measurements. They are only single observations, and were taken before I had succeeded in getting anything like the same sensitiveness I can now attain in the apparatus. As illustrations of the fact, however, that the more refrangible rays of the spectrum act as well as the lower rays, they may be taken as trustworthy.* 112. In my former paper on this subject I have already mentioned in detail that at a certain point of rarefaction there is neither attraction nor repulsion when radiation falls on the movable index (30, 43, 47, 66). I have long tried to ascertain the law governing the position of this neutral point. My results are not yet ready for publication; but they are shaping themselves in order, and will, I trust, lead to a true explanation of the cause of these phenomena.

The barometric position of the neutral point dividing attraction from repulsion varies according to circumstances; among these may be mentioned the density of the substance on which radiation falls, the ratio of its mass to its surface, its radiating- and conducting-power for heat, the physical condition of its surface, the kind of gas filling the apparatus, the intensity of radiation, and the temperature of the surrounding atmosphere.

When the surface exposed to radiation is pith, the neutral point is somewhat low. I have had it vary between 50 millims. and 7 millims. (30) below a vacuum. It is, however, impossible to ascertain exactly; for a point of rarefaction can be obtained at which the warm fingers repel, and incandescent platinum attracts. With a heavy metal in the form of a sphere, so as to expose the smallest surface in proportion to the mass, I have not attained the neutral point until the exhaustion was within a very small fraction of a millimetre (43, 47); whilst if the metal is in the form of thin foil the neutral point may easily be got lower than with pith.

I am inclined to believe that the true action of radiation is repulsion at any pressure, and that the attraction observed when the rarefaction is below the neutral point is caused by some modifying circumstance connected with the surrounding gas, not necessarily of the nature of aircurrents (80). As a proof of this I have not unfrequently, obtained repulsion from radiation when the apparatus was full of air at the normal pressure.

113. The following experiments are too few in number, and have not been varied sufficiently as to conditions, to enable many inferences to be drawn from them. However, they afford glimpses of a law governing the position of the neutral point.

A torsion-apparatus was fitted up similar to the one

Everything is ready to try a series of experiments with the solar spectrum, as soon as sunshine is available. The results shall be communicated in a subsequent paper.

described in paragraph 102. The beam was of glass, and at one extremity was fitted with a spring clip, also of glass, so that different bodies could be experimented with. Disks of platinum foil, 1 centimetre in diameter and weighing 128 grs. each, were prepared, and they were fixed in the clip at the end of the torsion beam, either singly or two, three, or four together, in such a manner that while the disk exposed was always I centim. in diameter, the weights should be in the proportion I, 2, 3, 4. At the other end of the beam a movable counterpoise was arranged, so that the length of beam from the platinum disk to the centre was always the

CHEMICAL NEWS,
Dec. 15, 1876.

The crystals selected for the analysis were about inch long, of a clear dark green colour, and perfectly transparent.

It was desired to ascertain the combined action of heat and air on oxychloride of copper. For this purpose a portion of the substance employed in the above analysis was placed in the centre of a combustion tube between two plugs of asbestos; air from a gas holder was passed slowly through the tube, while the latter was heated gradually up to the highest temperature obtainable with a charcoal combustion furnace. This temperature was maintained until the sublimate did not appear to increase further in quantity. When cold the contents of the tube were examined. At the cooler part of the tube a sublimate had formed varying in colour from light yellow to dark brown. On examination this proved to be subchloride of copper. In the place of the original substance there remained a brilliant black fritted mass of protoxide of copper. The internal portion of the tube extending for a short distance from the point where the original substance was placed, towards that part of the tube where the sublimate had formed, was converted into a bluish green glass. At the commencement of the experiment, when the temperature was comparatively very low, oxygen was evolved. I do not know whether this reaction has been noted before, but it is readily observed on heating a small portion of atacamite in a test-tube.

The experiment detailed above was repeated, the atacamite powder in this case being placed in a platinum boat, all the other conditions remaining the same; the results were identical with those obtained in the former experiment. The reaction which takes place when oxychloride of copper is heated with access of air would therefore appear to be as follows:

CuCl2+3CuO+4H2O=Cu2Cl2+2CuO+O+4H2O.
Laboratory, Wallaroo Smelting Works,
Wallaroo, South Australia,
October 5, 1876.

BUTTER ANALYSIS.

AN IMPROVED METHOD OF ASCERTAINING
THE SPECIFIC GRAVITIES OF FATS.

By C. ESTCOURT, F.C.S.

Analyst to the City of Manchester, Borough of Oldham, &c.

THE great advance which has been made in food analysis since the passing of the "Food Adulteration Act of 1872" is nowhere so apparent as in the methods employed to detect adulterations in butter. It is scarcely three years since the time when the only methods of butter analysis, so-called, consisted entirely of smelling and tasting. Thus we had a butter taste, a tallow taste, and a lard taste. The first advance made was the observations of the fusing-points of different fats, and the next one was the estimation of the fatty acids present in fats of various origin. The last named process has, since its discovery by Messrs. Angell and Hehner, been so elaborated by various workers, amongst whom are Drs. Dupré and Muter, that nothing further in this direction can be expected.

The process, however, which recommends itself by its simplicity, and its good results, if properly carried out, is that of taking the specific gravities of various fats, butter fat amongst others. This process, devised by Mr. James Bell, F.C.S.,principal of the Inland Revenue Laboratory, has only been slightly modified since its first application. The modifications were the change of temperature in the water used to compare with the fat, and the use of specific gravity beads.

In ascertaining the presence of, and estimating the quantity of foreign fat in butter by either the fatty acid, or the ordinary specific gravity method, several difficulties present themselves. In the first

CHEMICAL NEWS,
Dec. 15, 1876.

New Method of Separating Nickel and Cobalt.

255

fatty acid and the gravity bottle method) arrive at the same results. It will be observed that the ordinary way of calculating the amount of foreign fats is rather in favour of the vendor of the adulterated article, as equal weights of fats mixed do not produce exactly average gravities, as at first sight might have been supposed. In conclusion I may point out that each observer should test his balance and apparatus with the various fats, as the stationary temperature of his own apparatus may slightly vary from 208 F.

method the possible loss in manipulation, and the tedious | this method that a dozen observers will (unlike in the nature of the process (shortened as it has been) are strong objections. In the second method no objection can be made as to the time occupied, but a serious consideration is the extreme care necessary in taking gravities at so high a temperature as 100° F. by means of a specific gravity bottle. Those who have tried a large number of these determinations will see how difficult it is to be certain that the gravity bottle is filled with the fat and cleared of all outside deposits exactly at 100 F. A degree, more or less, is quite equal to 0.5 in the gravity, and this difference will certainly occur where two operators are examining the same sample, and sometimes in two experiments by the same operator.

Having tried all these methods with fair success I was led, by the considerations I have stated, to try whether the specific gravity of fats could be taken by means of a specific gravity balance, working by immersion, the tube containing the fats being kept at a constant temperature. Naturally my first idea was the water or steam bath, and I may say at once that no objection can be taken to it on the ground of high temperature, as the first step in all processes for butter analysis is to heat it on the bath until the curd and water deposit.

I found, however, that the steam constantly deposited on the beam of the balance, and thus affected the results. I therefore devised a method free from this inconvenience, and which I have found to give exceedingly constant results.

The balance I use is one made by G. Westphal, of Celle, Hanover, and works very accurately. The bulb of this balance is suspended in the test-tube (1 in. by 5) which contains the fat. This test-tube is immersed in a metal tube containing paraffin (any other substance with high boiling-point will do), which is closed at the bottom. This tube is fastened securely by luting, &c., on to the lid of a small water-bath of suitable size, which has an outlet for steam, to which a glass tube can be attached, and a tube at the side to indicate the quantity of water in the bath.

same.

The modus operandi is as follows:-The water-bath is fitted up to the proper height, which should be always the The metal tube is filled with paraffin, and when (heat having been applied) the paraffin is melted a thermometer is placed on it and the test-tube of fat. When the fat is melted the balance is adjusted, the bulb is immersed in the fat, and the weights (approximate) are placed on the beam. When the temperature of the paraffin indicates 206° F. I exactly adjust the weights, and then when it becomes stationary for a minute, which it does in my bath at 208° F., I put the exact weights on, allow it to remain in equilibrium for five minutes, then record the weight, which is the specific gravity of the fat under examination.

I give below the results of a series of experiments with this apparatus.

No.

Temperature of Paraffin
Bath 20S° F.
Specific Gravities.
Found. Calculated.

Description of Fat.

NEW METHOD OF SEPARATING NICKEL
AND COBALT.

By ANTHONY GUYARD (HUGO TAMM).

THE alkaline sulphocyanides exert an unequal action on the sulphides of nickel and of cobalt recently precipitated. In the cold we do not observe a very marked action, but on raising the temperature we see the sulphide of nickel enter into solution with a very great facility, whilst the sulphide of cobalt resists more, and only dissolves even in a considerable excess of sulphocyanide, after prolonged boiling. This reaction is not sufficiently distinct for analytical application, but by a modification we render it practical, and find ourselves in possession of a very elegant and very exact method of separating nickel from cobalt. In fact, in cold and very dilute liquids, the sulphide of nickel recently precipitated is dissolved with a surprising rapidity in cyanide of potassium, whilst sulphide of cobalt is perfectly insoluble. In these conditions the reaction is so clear and distinct that we may find in the oxide of nickel traces of cobalt (which we could only detect by the aid of the blowpipe), and effect their separation.

In the course of an analysis the best way of proceeding is as follows:-We separate, in the usual manner, the cobalt and nickel from the metals which accompany them; then we precipitate both by a slight excess of sulphide of ammonium. We dilute the liquid with a suitable quantity of water; then add gradually a weak solution of cyanide of potassium, avoiding excess. This operation is rendered easy by the fact that the mass of sulphides clears up, and the sulphide of cobalt floats in particles detached from each other, and we distinctly see what passes in the liquid. We then filter, collect the sulphide of cobalt, and determine the cobalt in the ordinary way. To isolate the nickel we acidulate the filtered liquid with a slight excess of muriatic or sulphuric acid. The nickel is precipitated in the state of cyanide, and that so completely that we cannot find traces of it in the liquid. This cyanide is collected upon a filter, well washed, then calcined. Oxide of nickel is thus obtained so pure, in some cases, that it may be weighed and determined at once as nickel. However, in general, it is prudent to purity this oxide, which often retains silica: in this case we proceed in the ordinary manner.

The advantage of the process which I propose for the separation of nickel and cobalt is that it permits us to determine the nickel without having to manipulate it in the state of sulphide-an operation always long, very delicate, and very troublesome.

Under favourable circumstances the analytic process that I have just explained will certainly be one of the most simple processes, and may be applied to the separation of nickel and cobalt on a large scale.-Bulletin de la Société Chimique de Paris.

Project of a Great Aquarium.-At the Exhibition to be held at Paris, in 1878, M. Toselli proposes to construct a great aquarium to serve for the display of divingbells, instruments for raising sunken ships and their cargoes, &c.-Les Mondes.