Page images
PDF
EPUB

The addition of artificial colouring matters such as the naphthol oranges may be readily detected by extracting the berries with alcohol in which such colouring matters are soluble, whilst genuine coffee does not yield a coloured solution.

The great inconvenience and difficulty of estimating the specific gravity of such a substance as coffee by the ordinary method with water, may be avoided by estimating the displacement of air due to a known weight of the berries by the following process. A weighed quantity of from 50 to 100 grams is placed in an air-tight cylinder the exact capacity of which is known, the air in the cylinder is then compressed by allowing mercury to rise to a given height in a tube attached, the usual corrections having then been made, the height of the mercury in a manometer gives the tension of the air in the cylinder, and the difference between this tension and the tension under similar conditions when the cylinder contains nothing but air indicates the volume of air, and hence the volume of solid matter contained in the cylinder. By this means very rapid and satisfactory determinations may be made. A drawing and full description of the apparatus employed by the author are given in the paper.

A. P.

Detection of Albumin in Urine. By L. BLUM (Chem. Centr., 1887, 345). The usual test for the detection of albumin in urine, namely, the formation of a white coagulum on addition of metaphosphoric acid, is inconvenient on account of the ready conversion of the meta- into pyro- or ortho-phosphoric acid. Instead of the free acid, the author prefers to use an acidified solution of a manganese salt to which has been added an excess of sodium metaphosphate. This can previously be tested by the addition of lead peroxide, which gives a rose-red coloration. The detection of the albumin is best effected by placing a few c.c. of the above solution in a test-glass and filtering the urine into it, when the albumin separates at the junction of the two liquids. V. H. V.

Determination of Milk Constituents. By R. PALM (Zeit. anal. Chem., 26, 319-330).-By most of the existing methods of milk analysis, albumin and casein are the only proteïds determined, and the whole reducing power of the filtrate is ascribed to milk-sugar. Since, however, hemialbumose and the (perhaps identical) lactopeptone of Millon and Commaille escape precipitation by the ordinary reagents and are capable of reducing Fehling's solution, the proportion of milk-sugar is over-estimated, and that of the total proteïds understated. Ritthausen's copper sulphate process suffers from this defect. Tunnin, however, precipitates all the proteïds. The fresh precipitate digested at 30-35° with an excess of neutral lead acetate yields lead tannate and a solution of the proteïds in excess of lead acetate. After precipitating the lead by hydrogen sulphide, the amount of the proteïds is found by evaporating the filtrate and drying at 100°. Mercuric nitrate or acetate likewise precipitates all the proteïds, and by adding potash concurrently with the mercuric solution and finally in small excess, the solvent action of free acid or of an excess of mercuric salt

is prevented. A determination of the oxide of mercury (after drying at 100°) gives the proteïds by difference, or the fresh precipitate can be heated with baryta, the barium carefully precipitated by sulphuric acid and the proteïds weighed after evaporating the filtrate. A process which the author recommends for milk is as follows:-10 c.c. are evaporated to dryness; the residue is washed with light petroleum to remove fat, then with ether, which dissolves a small quantity of lactic acid formed during the evaporation, and therefore ought not to be employed for the fat determination. It is then well mixed with 0.2-0.3 gram of finely-ground ignited litharge and enough water to form a paste. This is again dried and then treated with water, when a clear filtrate is readily obtained containing the milk-sugar with some lead, whilst all the proteïds are left as an insoluble lead compound. The amount of each is ascertained by weighing after drying and then burning off the organic matter, using nitric acid to prevent reduction of lead. M. J. S.

1005

General and Physical Chemistry.

Influence of Simple and of so-called Multiple Union of the Atoms on the Refractive Power of Compounds. Constitution of Benzene and Naphthalene Compounds. By J. W. BRÜHL (Ber., 20, 2288-2311).-Gladstone showed that the molecular refraction of aromatic compounds is always in excess of the value calculated from Landolt's formula. The author observed a similar excess in the case of all unsaturated compounds which are supposed to contain double union of atoms, the extent of the excess being dependent on the number of double combinations present. The atomic refraction of the saturated carbon-atom rC' 2:48, remains the same whether the four affinities are satisfied by single carbon-atoms or by monatomic substituents. Hence if benzene is represented by nine single carbon combinations it would possess a normal molecular refraction.

The molecular refractions of aldehyde and paraldehyde are 11.50 and 32:40 respectively; the latter number is three times the former less 2:10. This number is nearly the same as that obtained by multiplying the refraction-equivalent of the double combination of oxygen and carbon (3 × 0·76 = 2·28).

Tables are given showing the molecular refraction of hydrocarbons C5H10, C10H, and C10H16. The following conclusions are drawn :That a so-called double combination of atoms is never optically equivalent to two single combinations, and that in the conversion of the former into the latter the increment of refraction disappears entirely or partially according as all or a portion of the multiple combinations. are taken up. The author discusses the constitution of benzene, and considers Kekulé's formula to be established; carvacrol and carvol are probably constituted on the same model. Tables are given showing the refraction-equivalents of naphthalene and some of its derivatives; the numbers point to the presence of five ethylene combinations in naphthalene as shown in Erlenmeyer's formula. N. H. M.

Fluorescence of Spinel. By L. DE BOISBAUDRAN (Compt. rend., 105, 261-262).-Spinel usually gives a brilliant red fluorescence in a vacuum, but some specimens show a green fluorescence.

If a mixture of magnesia and alumina free from chromium is strongly heated, it yields spinel in fine granules which show no red fluorescence in a vacuum. A feeble green fluorescence is, however, visible, and its spectrum shows the green band observed with the green fluorescence of natural spinel. If the artificial spinel contains 01 per cent. of manganese oxide, it shows an intense green fluorescence, the spectrum of which consists of the same band. If 1 per cent. of chromic oxide is added the spinel shows a splendid red fluorescence. It follows that the green fluorescence of natural spinel is due to the presence of manganese, and the red fluorescence is due to the presence C. H. B.

of chromium.

VOL. LII.

3 y

This

Crimson Line of Phosphorescent Alumina. By W. CROOKES (Proc. Roy. Soc., 42, 25-31).-The author has repeated his previous experiments on this subject (Phil. Trans., 1879, 660; Ann. Chim. Phys., 1859, 57, 50; Proc. Roy. Soc., 32, 206), and now gives careful measurements of the spectrum of phosphorescent alumina. consists of a very faint pair of hands in the red, an intense crimson double line (= 6942 and 6937), a pair of faint and nebulous orange lines (6707 and 6598), and a continuous spectrum commencing at 6514 and shading off into the green. The spectrum is different from that of spinel, first described by Becquerel, which shows a faint double band in the extreme red, a narrow crimson line (A = 6857), four hazy red bands, and sometimes a continuous spectrum most intense in the green, and shading off gradually to blue and violet. A detailed description of this is given.

De Boisbaudran (this vol., p. 191) attributes the red fluorescence of calcined alumina, when submitted to the electric discharge in a vacuum, solely to the presence of chromic oxide. The author, however, has obtained the double line from pure alumina, quite free from chromium; and has found, moreover, that the line is reduced in intensity when a little chromium oxide is mixed with the alumina.

Alumina precipitated from its ammoniacal solution by boiling shows no crimson line, but simply a greenish phosphorescence; the red line is fully developed only when the earth is calcined at the highest temperature of the blowpipe flame. The author's previous experiments prove that physical differences may greatly influence the phosphorescence. In view of the possibility of the line belonging to some special variety of the earth, he has submitted pure alumina to three separate processes of fractionation, the operations being repeated 20 to 30 times in each case. Details are not given; but the result was that alumina giving the crimson line became concentrated towards one end of the fractionation, whilst the earth accumulating at the other end phosphoresced either green or hardly at all. Chromium was in no case detected.

It is thus still uncertain whether the line is due to alumina, but capable of being suppressed by the presence of some other earth; or if the line belongs to some accompanying earth; or if it depends on the mode of preparation of the alumina; or, lastly, if the molecule of ordinary alumina is complex and the line belongs to one of its constituents. CH. B.

Fluorescences of Manganese and Bismuth. By L. DE BOISBAUDRAN (Compt. rend., 105, 45-48 and 206-208; see also this vol., pp. 3, 4, 89, and 873). The author has continued his researches, and has examined the fluorescences of a mixture of two solid solvents behaving towards one another as moderately active substances, and a third substance strongly fluorescent with one of the solvents only, as represented by a mixture of cadmium sulphate (100 parts), bismuth sulphate (10 parts), and calcium sulphate. With a proportion of calcium sulphate not exceeding 148 per cent., the calcium cadmium fluorescence is prevented by the presence of bismuth, although the calcium bismuth fluorescence is not visible. When the quantity of calcium

sulphate exceeds 16.1 per cent., the calcium bismuth fluorescence becomes visible, and increases in brilliancy with the proportion of calcium sulphate.

The author has also investigated the properties of a mixture of two solid solvents, the first of which (a) behaves towards the second (B) as a moderately active substance, and two active substances, one of which fluoresces with both solvents, and the other with only one of them. These conditions are fulfilled by a mixture of calcium, cadmium, bismuth and manganese sulphates. With an excess of calcium sulphate, the calcium manganese fluorescence is strongest, the calcium bismuth fluorescence much weaker, and the cadmium manganese fluorescence is not visible. With an excess of cadmium sulphate, the cadmium manganese fluorescence is predominant, the calcium manganese fluorescence is also visible, but the calcium bismuth fluorescence cannot be recognised.

The author's experiments lead to the following general conclusions. A substance may show strong fluorescence when disseminated through another substance, and yet show no Яuorescence with a third substance closely analogous to the second. A substance may fluoresce strongly with one compound of a metal and not at all with another compound of the same metal; or it may show fluorescence of a different character in the second case. Strongly coloured substances prevent the fluorescence of active substances by reason of their strong absorptive power. A substance may behave as a solvent to one active substance; and also behave as a more or less active substance itself when mixed with a third substance. When two active substances coexist in the same solvent their individual fluorescences are reduced in intensity, but their spectral character is not altered. Two more or less active substances in the same solvent may, however, neutralise one another. A substance which is active under certain conditions, but is inert when mixed with a particular solvent, may yet reduce the effect of a substance which is usually active with this solvent. Fluorescence in a given solvent seems as a rule to diminish on the addition of a second solvent which is not so effective with the active substance as the first solvent, but in some cases this effect is very slight. An active substance generally produces a double fluorescence with a mixture of two active solvents, but with certain proportions one of the fluorescences diminishes in a greater ratio than the quantity of the solvent which produces it. With one active substance, and equivalent quantities of two effective solvents, the two fluorescences usually are equal in intensity, but the contrary is observed in certain cases. If two substances are unequally active with a given solvent, and the ratio of the two is kept constant whilst the proportion of the solvent is gradually increased, it is possible in some cases to observe successively (1) the effect of the less active body alone, (2) the coexistence of the two effects with increasing predominance of the effect of the more active substance. When the proportion of the more active substance is increased, its effect alone is observed whatever the nature of the solvent. Certain fluorescences which are masked by others can be seen when the tube is heated, or by observing immediately after the cessation of the electrical discharge, or by modifying the strength of the discharge. C. H. B.

« PreviousContinue »