tained 0.1 to 10 grams of tannin dissolved in 500 c.c. of water. The ordinary solutions are prepared by boiling and pressing the material four times; they are made up to a definite volume and to a gravity of 1° B. or less, then a measured quantity is shaken with powdered skin, and the next day is filtered, pressed, &c. It is important to use dry and assayed powdered skin as well as good instruments.

D. A. L.

Peptones in the Blood and Urine. By GEORGES (J. Pharm. [5], 13, 353-354).-All the methods hitherto proposed for the detection of peptones in urine are more or less defective. The author gives the preference to the two following:

I. This has been recently employed by Wassermann for the detection of peptones in the blood. The blood is received in strong alcohol; the clot thrown on a filter is washed first with cold then with boiling water; the aqueous solution is concentrated to about double the volume of the blood taken, and then added to the alcoholic solution; sodium acetate and ferric chloride are now added to the liquid. After filtration and cooling, the last traces of albumin are removed by adding potassium ferrocyanide and acetic acid, filtered, the excess of ferrocyanide precipitated by copper acetate, filtered, excess of copper removed by hydrogen sulphide; filtered again, and heated on the water-bath to expel hydrogen sulphide and to concentrate the liquid. This method gives good results, especially if care be taken to neutralise, or even to add a slight excess of alkali on adding the sodium acetate and ferric chloride. It also serves very well for the investigation of peptones in urine, commencing by boiling to precipitate albumin coagulable by heat, and terminating as above.

II. The double iodide of potassium and mercury precipitates albumin and the peptones, and Tanret has shown that the albuminous precipitate is insoluble in boiling acetic acid, whilst the peptone precipitate dissolves completely. Employing these reactions, Georges has established a much more rapid method as follows:-Precipitate by heat all the coagulable albumin; treat the urine with acetic acid and the double iodide, wash the precipitate on a filter with cold water charged with acetic acid to the same extent as the urine; wash again with the same acidified water boiling, keeping the washings apart. The clear liquid obtained gives a precipitate on cooling if the least trace of peptonic precipitate has been dissolved. It is only necessary to neutralise in order to obtain a solution to which the double iodide test can be applied. J. T.

189

General and Physical Chemistry.

Actinometry. By E. DUCLAUX (Compt. rend., 103, 1010-1012). -Oxalic acid in aqueous solution is converted into carbonic anhydride and water by the action of light in presence of oxygen, and this decomposition is not due to any rise of temperature resulting from absorption of the sun's radiation, but is brought about by the visible and ultra-violet rays. In order to secure sufficient contact with the oxygen of the air, the solution is placed in flat vessels and the same volume of liquid is always employed; also, in order to eliminate the somewhat considerable influence of the concentration of the solution, a dilute solution, containing 3 grams of oxalic acid per litre, is employed. The amount of change is determined by titrating with lime-water. If the solution of oxalic acid has been kept for about two months in the dark, it is found to be much more sensitive to the action of light than a freshly prepared solution-a fact which indicates that the two liquids have not the same molecular constitution. The change is analogous to the ripening of collodion. The same degree of sensitiveness can be imparted to a freshly prepared solution by exposing it to sunlight for a few hours, and if a concentrated solution is treated in this way and is then diluted to the strength given, the increased sensitiveness is transmitted to the dilute solutions-a fact which indicates that the alteration takes place in the molecules of the acid and not in those of the water.

The total quantity of acid decomposed when the same quantity of liquid is exposed during the whole day is much greater than the sum of the quantities decomposed when a fresh portion of solution is exposed during each hour, the difference varying from day to day. There is therefore a period of quiescence similar to that which is observed in many photographic and chemical reactions, and which Bunsen and Roscoe have termed photochemical induction in the case of hydrogen and chlorine. C. H. B.

Fluorescences of Manganese and Bismuth. By L. DE BOISBAUDRAN (Compt. rend., 103, 1064-1068).—A mixture of 100 parts of yttrium sulphate with 2 parts of manganese sulphate shows a yellowish-green fluorescence, the spectrum of which consists of a broad band which begins at about 6500, attains its maximum brilliancy at 5640, and fades away gradually at 4890-4840. With 4 per cent. of manganese sulphate, the fluorescence is more intense, but its character is not altered. The fluorescence differs from that of calcium, and is not due to the presence of traces of this element. A mixture of 100 parts of yttrium sulphate with 2 parts of bismuth sulphate gives a red fluorescence, with a spectrum consisting of a band which begins at 6840, attains its maximum brilliancy at 6420-6400, and fades away at 5790-5770. This fluorescence is not due to the presence of magnesium.

VOL. LII.

0

Calcium sulphate mixed with small quantities of both bismuth and manganese sulphates gives a fluorescence which is yellow at the centre, and pale-green further from the electrodes. In the spectrum, the orange-red band of the calcium-bismuth fluorescence is very distinct. If the tube is heated, the fluorescence becomes rose-yellow, the red band is scarcely affected, and the brilliancy of the green is diminished. At a higher temperature, the fluorescence diminishes and again becomes green with a bluer shade than originally, and the red band is almost extinguished. In all cases, the fluorescence is much less brilliant than with calcium and manganese sulphates free from bismuth.

A mixture of magnesium sulphate with both manganese and bismuth gives a fluorescence due to the superposition of the magnesium-manganese and the magnesium-bismuth fluorescences.

Cadmium sulphate with small quantities of both manganese and bismuth gives the cadmium-manganese fluorescence, which is somewhat less brilliant than in the absence of bismuth. Strontium sulphate, on the other hand, under similar conditions, gives the strontiumbismuth fluorescence, the intensity of which is somewhat diminished by the presence of manganese.

A mixture of calcium oxide with small quantities of manganese and bismuth oxides gives the calcium-manganese fluorescence with somewhat diminished intensity.

A mixture of zinc and calcium sulphates, in varying proportions, with small quantities of manganese, gives a fluorescence in which the calcium-manganese fluorescence is much more prominent than that due to zinc-manganese. With only 5 per cent. of calcium sulphate, the effect of its presence is readily observed, and it is quite distinct with even 2 per cent. if the tube is heated.

C. H. B.

Effect of Manganese on the Phosphorescence of Calcium Carbonate. By E. BECQUEREL (Compt. rend., 103, 1098-1101).The most highly phosphorescent crystals of Iceland spar, which show an orange phosphorescence, contain a somewhat high proportion of manganese, probably in the form of carbonate, with mere traces of iron. The less strongly phosphorescent varieties contain very little manganese.

Calcium carbonate, precipitated from a solution of calcium chloride containing 4 per cent. of manganese chloride, gives almost identical results. Calcium carbonate, formed on the surface of such a solution when exposed in an atmosphere charged with the vapour of ammonium carbonate, does not show the same phenomenon.

These results explain the author's earlier observation, that calcinm carbonate precipitated from calcium chloride prepared from Iceland spar, always gives an orange phosphorescence, whilst that prepared from aragonite shows a green phosphorescence. Further experiments are necessary to determine whether manganese is the sole cause of the phenomenon.

The phosphorescence of Iceland spar is affected by lithium, bismuth, and antimony, and by various metallic sulphides.

C. H. B.

Red Fluorescence of Alumina. By L. DE BOISBAUDRAN (Compt. rend., 103, 1107).-Pure calcined alumina shows no red fluorescence when subjected to the action of the silent discharge in a vacuum, but the red fluorescence described by Becquerel ("La Lumière") is shown brilliantly if the alumina contains a small quantity of chromic oxide, and is visible even with so small a proportion as 0·001 per cent. Alumina with 1 per cent. of manganese oxide shows a green fluorescence; with 1 per cent. of bismuth oxide, a lilac fluorescence in the cold, which becomes blue on heating. Magnesia with 1 per cent. of chromic oxide shows a red fluorescence, whilst the fluorescence of lime containing chromic oxide differs very slightly from that of pure lime. C. H. B.

Phosphorescence of Alumina. By E. BECQUEREL (Compt. rend., 103, 1224-1227).-The alumina prepared by Boisbaudran (preceding Abstract) does actually show a feeble red phosphorescence, but after being heated to a very high temperature in a platinum crucible for 15 minutes, it shows the red phosphorescence brilliantly. It would seem, therefore, that Boisbaudran had not sufficiently dehydrated his product.

The author has repeated his earlier experiments, and confirms his former conclusion that pure alumina shows some phosphorescence, which is often greenish in colour, but if strongly heated it shows a brilliant red phosphorescence, the intensity of which is increased by the presence of small quantities of chromium and certain other substances. He points out that the exact character of a phosphorescence or fluorescence will depend on the agent by which the substance is excited and the conditions under which excitation takes place.

C. H. B.

Molecular Refraction of Liquid Organic Compounds of High Dispersive Power. By J. W. BRÜHL (Annalen, 235, 1106; see also Ber., 19, 2746).-In previous papers (Abstr., 1880, 293, 295, 685, 781; 1881, 15; 1882, 263, 445, 827, 829), the author has shown that the mode of union of atoms in a compound, independently of their mere number, has a special influence in raising the molecular refractive power. The present paper embodies a number of new and confirmatory observations, together with discussions of the validity of the several expressions for molecular refractive power, and of the possible connection between dispersion and refractive index or chemical constitution. Numerous references to the work of other physicists are given. The methods of investigation have been previously described.

The first part of the paper contains an account of the preparation and purification of 21 unsaturated compounds specially examined, together with determinations of their densities, refractive indices for the lines a, D, 6, and 7, their molecular refractive powers according 1). and the more recent

to Dale and Gladstone's formula (μa

Р

d

&c. The constants for these and

for 21 other unsaturated compounds previously examined are arranged in four tables, from which subsidiary tables are constructed to illustrate special points.

Gladstone and Dale's constant was found to be correct within moderate limits of temperature, and since it was applied chiefly to the saturated and feebly dispersive compounds of the fatty series, comparable results were obtained. More recently, H. A. Lorenz (Ann. Phys. Chem. [2], 9, 641) and L. Lorenz (ibid., 11, 70) have proved by independent theoretical methods that the relation between the velocity of propagation of light and the density of the medium is n2 1 contained in the formula = constant, when n = refractive (n2 + 2jd index, d density. This constant was proved by these authors, and by Nasini and Bernheimer, to vary much less with the temperature than the old one. Landolt, also (Abstr., 1882, 909), by its aid has recalculated the molecular refractive powers of many compounds examined by various authors, and found not only that all the earlier established relations are equally well expressed, but that a closer agreement between theory and observation is attained by its use. There still remain, however, serious discrepancies between theory and experiment, especially in the case of substances of high dispersive power.

=

The question then presented itself: Is there any relation between. dispersion and mean refractive index on the one hand, or chemical constitution on the other?

Dispersion may be measured either as uy Bin Cauchy's equation

=

μ = A +

B C
+ +

λ

Ma, or by the constant

(using only constants A and B), in which μ = refractive index for wave-length A, A refractive index for infinite wave-length. In the saturated compounds of the fatty series, B is small (0-3 to 0.5); but in the unsaturated compounds tabulated in this paper B is very great, in the case of cinnamaldehyde reaching the enormous value 2.5. Calculating the constants A and B from observations of μα and My, the author has applied Cauchy's equation to calculating up for the lastnamed substances, and he shows by a tabular statement that theory and experiment agree well for compounds of low dispersion, but that very serious discrepancies arise when the dispersive power is high. Cauchy's equation is therefore untrustworthy in these cases. definite relation can be traced between dispersion and mean refractive index. (See also following Abstract.) Neither does any connection exist between dispersion and chemical constitution. This is shown by selected examples, in which (dispersion at 20° for

B

d20

No

unit density) is seen to have very different values for compounds of analogous constitution, nearly equal density and equal refractive index; whilst, on the other hand, the dispersion may be the same for substances of very different chemical structure.

Enquiry is next made into the validity of the old and new formulæ.