THE weighed substance, containing not more than o'2 grm. of K2O, is to be treated, after dissolving it in a few c.c. of hot water, with a clear concentrated solution of caustic baryta, and heated for about ten minutes. The liquor now contains the alkaline salts and BaH2O2. By conducting in CO2, and heating afterwards to expel the free CO2, the solution retains the alkaline salts only. A drop of pure Na2CO3 added to the clear liquor ascertains if the preceding operations are complete. The clear liquor may be filtered and washed with hot water by means of an aspirator.

If properly managed, the liquor does not exceed 250 c.c. After concentrating it in a platinum dish on the waterbath, a few c.c. of HCl are added, the evaporation continued to dryness, the residue dissolved in a little hot water, and, after adding 1 grm. of PtCl in about 10 c.c. of water, again evaporated till dry, but at about 90° C. only. By mixing the cold residue with alcohol of So per cent, the insoluble PtC14.K2Cl2 may be collected on a filter after about half an hour, washed with alcohol, and dried. The precipitate is reduced by heating it with a little pure oxalic acid to platinum, which is then weighed.

Goulding's Manure Works, Dublin,
May 10, 1875.

REPORT ON THE

DEVELOPMENT OF THE CHEMICAL ARTS
DURING THE LAST TEN YEARS.*
By Dr. A. W. HOFMANN.
(Continued from page 222).

Wagner, Jahresberichte, 1867, 216.

Archereau, Dingler's Polyt. Journ., clxxviii., 57. Wagner, Jahresberichte, 1867, 215.

§ Pepper, CHEMICAL NEWS, 1862, 218.

the latter difficulty by adding to the nitre oxide of zinc. 20 lbs. of soda-saltpetre and 4 lbs. of crude oxide of zinc yielded in his hands 94.676 cubic feet of a mixture of 59 per cent of oxygen and 41 per cent of nitrogen, the residue being chiefly oxide of zinc and caustic soda. In this mixture, which is useful for many purposes, the oxygen cost 2.32 francs per cubic metre if the solid residue be neglected; but, if the latter be utilised, the expense of the oxygen falls to 0.78 franc.*

In all these methods, one of the leading ideas of modern industry, the regeneration of residues, has been neglected. The following proposals are, in this respect, happier, and have, therefore, been partially more successful. To combine the oxygen of the atmosphere chemically with some substance which shall readily give off the combined gas, and be again able to take up and give off fresh quantities of oxygen, as is done by the mercury in mercuric oxide; this is the problem which has been solved in the last few both oxide of copper and the peroxides of nickel and cobalt, years. As early as 1829, Dingler, Junior,+ observed that with an excess of chloride of lime, gave off oxygen, converting the latter substance into chloride of calcium. In 1845, Mitscherlicht made known the fact that various other metallic oxides, peroxide of manganese, hydrated peroxide of iron, &c., if added to a solution of chloride of lime, occasioned a plentiful liberation of oxygen. In 1865, these observations were renewed by T. H. Fleitmann, || with especial reference to recently prepared sesquioxide, small quantities of which sufficed to decompose completely a concentrated solution of chloride of lime into chloride of calcium and oxygen gas. He recommended, in practice, a solution of chloride of lime concentrated as much as possible, and clarified by filtration or deposition to prevent frothing, and then mixed with o'1 to 0.5 per cent of its contents of sesquioxide of cobalt, and heated from 70° to 80°. On employing chloride of lime at 35 per cent, he obtained oxygen in a regular stream, to 25 or 30 times the volume of the liquid. Other observers, especially F. Varrentrapp,§ confirmed these results, and recommended the industrial adoption of the process. The sesquioxide of cobalt does not require to be manufactured in advance. Any salt of cobalt in solution serves the same purpose, and the sesquioxide settles to the bottom and can be used again in fresh operations. (To be continued.)

ON AMMONIO-SILVER CARBONATE. By SERGIUS KERN, St. Petersburg.

By adding, to a concentrated solution of silver carbonate (Ag2CO3) in ammonia, ethyl-alcohol (C2H6O), a peculiar grey precipitate is received, containing the elements of ammonia. In order to study the reactions and the nature of this compound, some experiments were made, the results of which are as follows:

The silver carbonate was prepared by mixing concentrated aqueous solutions of hydric sodium carbonate (HNaCO3) and silver nitrate. The yellowish precipitate of silver carbonate obtained was well washed and dried over sulphuric acid; the dried salt was dissolved in ammonia, o'930 sp. gr., and from this solution the ammonio-silver carbonate compound was thrown down by means of absolute alcohol; the resulting grey precipitate was washed and dried. The ammonio-silver carbonate thus obtained gave the following reactions :

(1). The compound in the state of perfect dryness takes a more intense dark colour; some drops of ammonia im

Dupré, Comptes Rendus, Iv., 736.

+ Dingler's Polyt. Journ., xxvi., 231. Mittscherlich, Pogg. Ann., lviii., 471. Ann. Chem. Pharm., cxxxiv., 64.

§ Mittheilungen f. d. Gewerbe Vereins des Herzogthums Braunschweig, 1865-66, 72.

232

100°

160° to 170°

240°

305°

The substance blackens.

Conversion into a uniform black mass. The substance partly whitens from the decomposition into metallic silver.

.. Conversion into metallic silver. (4). A solution of ammonio-silver carbonate in ammonia, dried over calcium chloride, gives needle-shaped crystals of irregular form. The crystals dissolved in ammonia turn black, and the undissolved part falls down in the form of a black powder.

(5). The ammonio-silver carbonate, in the form of a black powder, resulting from the experiment No. 4, was dissolved in hydrochloric acid. There was a strong reaction, evolution of gas, and production of silver chloride (AgCI) and of a small quantity of neutral ammonia carbonate [(NH4)2CO3], by the following reaction :— Ag2CO3.4NH3+2HCl=2AgCI+(NH4)2CO3+2NH3. The presence of the ammoniacal salt was proved by testing the salt by means of a concentrated solution of sodium hydroxide (HNaO); ammonia gas was received from the decomposition of the salt :

(NH4)2CO3+2H NaO=Na2CO3+2NH3+2H2O. (6). The ammonio-silver carbonate may be considered as a direct compound of silver carbonate and ammonia, having the formula Ag2CO3.4NH3. At ordinary temperatures, this substance is a stable compound, which may be preserved for a long time without alteration; but, as it is seen from the experiments, it is readily decomposed by the action of heat and acids, with the evolution of ammonia gas.

LECTURES ON THE MORPHOLOGY OF CRYSTALS

AT THE

CHEMICAL SOCIETY.

By NEVIL STORY MASKELYNE, M.A., F.R.S., &c. (Concluded from page 202.)

LECTURE XIV.

THERE remain to be considered, among the phenomena of crystallography, certain modes of grouping, or of association of crystals in obedience to particular laws, some of which present points of extraordinary interest to the student of physics. The first to be considered among these was that known as the case of twinned or macled crystals. Thus, two crystals parallel in position may be supposed to be the one fixed, and the other turned round an axis, generally the normal of a face through 180°. Sometimes the two crystals appear thus grown together, either in superficial juxtaposition, or else inter-penetrating one another, and that, sometimes, in such a way that parts or laminæ of the one crystal are interpolated between, and alternated with, lamina of the other crystal, sometimes with even microscopic minuteness. A result of this twinned character is the frequent occurrence of re-entering angles on the crystal.

Among the more singular varieties which arise out of this twin law are cases in which hemi-symmetrical forms have undergone this introversion. Thus, in the cubic stem, hemi-symmetrical forms of the type {k}

π

к

{CHEMICAL NEWS,

May 28, 1875.

may be twinned, yet so as not to produce a holo-systematic form, since evidence of the twinning is recognisable in the physical character of the faces. Another very interesting kind of twinning is one of which we may take the mineral boracite as an illustration, in which we find two correlative hemi-symmetrical forms of the type {hkl} united into a crystal which would carry all the faces parallel to those of a octahedron, but in such a way that, for instance, the tetrahedral faces of the one form, :{ III, present different physical properties from those which characterise the correlative form (III), among which the property of becoming, the one positively electric, and the other negatively electric, by increase of temperature, and again having these electricities reversed the faces of one of the tetrahedra are brilliant, and those as the temperature is lowered, is conspicuous. Further, sical properties going one way along a given direction in of the other dull. In such a case, it is clear that the phya crystal are not the same as the properties going the opposite way along it, and this polar character is also met with in crystals that are hemimorphous; that is to say, in which all the faces of a form on one of the sides of a plane (necessarily a unique plane) of symmetry are obliterated. Then, again, there are cases of a species of composition of hemi-symmetrical forms in which two correlative diplohedral, but hemi-systematic forms, as, for instance, two correlative rhombohedra are twinned in such a manner as to build up a holo-symmetrical form. Of this, quartz is a conspicuous example, the rhombohedra, {hkk} and {eff}, uniting to form the twelve-faced dirhombohedron, wherein, however, the physical dissimilarity character of the crystal, in spite of their geometrical of the faces of the two forms betray the composite equivalence.

rotatory polarisation of the light by crystals, and this Finally, we have to consider the singular case of would seem, so far as the few cases that connect this property with crystalline form serve to guide us, to be connected with a hemi-systematic character in the forms presented by the crystal. Victor von Lang has pointed out that, in all the cases so far known, such as the sodiumchlorate, quartz, lead hyposulphate, and sodium-periodate, the hemi-symmetrical forms belong to what in our phraseology would be a hemi-systematic type, of which only one face is extant for each extant normal. Such a generalisation would, if confirmed, preclude the possibility of rotatory polarisation in the orthorhombic, the clinorhombic, and the anorthic systems.

PROCEEDINGS OF SOCIETIES.

CHEMICAL SOCIETY. Thursday, May 20, 1875.

NEWS

found that, although milk taken from herds of cows exhibits great uniformity in composition, yet the milk from individual cows is liable to considerable variation; moreover, it is possible for good average milk to be watered to a limited extent without detection. He observed, also, from a comparison of the milk from cows fed on ordinary meadow grass and on grass from a sewage farm, that in the latter case the milk went putrid after thirty-six hours, and the butter became rancid rapidly compared with that made from the milk of cows fed on ordinary meadow grass. These effects were more apparent in spring than in the latter part of the summer. On three or four occasions, also, he noticed that, when the milk of cows fed on sewage grass was placed on a dialyser, the casein passed through the membrane, from which it would appear that the casein existed in these milks in a modified form. He then proceeded to notice the outbreaks of typhoid fever which had occurred at various places owing to sewagewater having been used to cleanse the dairy utensils, or to reduce the quality of rich milk to the lowest standard allowed by law, showing how important it was that there should be a supply of pure water to every dairy. Moreover, milk which had been exposed to sewer-gas from an untrapped drain, although on analysis it appeared to be unaltered in composition, yet when distilled at a low temperature (160° F.) it yielded a distillate which had a very offensive smell. It also caused intense headache, which was followed by diarrhoea. He also examined the milk of cows suffering from foot and mouth disease and from milk fever, and thought that the methods employed by Public Analysts were not sufficiently delicate to detect the slight physiological changes which may take place in so complex a fluid as milk.

The PRESIDENT observed that there were so many interesting points connected with the subject that it could not fail to elicit a valuable discussion.

Dr. GILBERT said the subject was one of very great importance. Mr. Smee had shown, not only that there was great variation in the milk of different cows, but of the same cow at different times, and yet the evidence he had brought against the use of sewage grass was derived from obvervations on one or two cows. Now that the demand for milk from the country to supply London was so great, it created quite a milk famine in some parts. If we employ the water system for sewage it must be passed on the land where it produces succulent food fit for cows. If the cows were fed entirely on sewage grass the milk was but little inferior to that from unsewaged grass, and with a proper addition of oil-cake the milk was excellent. The analyses in the Report of the Royal Sewage Commission made by Messrs. Way and Evans on the milk of cows fed for a long period on sewage grass and oil-cake showed that the amounts of casein, butter, sugar, &c., were very nearly the same as that of cows fed in the ordinary way, but, as might be expected, there was a slight deficiency in the butter and sugar. No doubt great mischief would arise when sewage-water was used to adulterate milk, or for cleaning the dairy vessels.

Mr. W. THORP asked whether the cows had been fed for some time previously on sewage grass, or were immediately transferred to it. This was a point of some importance, for the alteration of the diet from the drier to the more succulent one would cause the cows to get out of condition, which would necessarily affect the milk.

Dr. THUDICHUM said the lowness of the ash in the milk of those cows which had been fed on grains was a physiological question of some interest. The grains had been exhausted of their salts, and the food not containing the proper quantity, the cows would get out of condition. This might, perhaps, be obviated by adding the necessary salts to the food to make up for those removed from the grains.

Dr. THORNE gave some instances in which children fed on milk from cows suffering from foot and mouth disease had suffered from salivation and sore mouths. When the use of the milk was discontinued, the symptoms dis

appeared. In these cases, the children were at a farm, the milk came direct from the cow, and was used copiously and without dilution. After being allowed to cool, or to stand for some time, the milk did not appear to produce any injurious affect.

Mr. SMEE said there were a few points to which he must allude. Dr. Gilbert had stated that the cows were fed with sewage grass, but, as he parenthetically observed, with something dry added, such as oil-cake. It was this something dry which made all the difference, for when nothing but sewage grass was used the cows pined away and died. He must insist that cows cannot be fed on sewage grass alone. Another point was that the casein had become altered, and good cheese could not be made from the milk. He had invariably found that the butter from his own herds, which was ordinarily very good, became so rank and bad when sewage grass was used for the cows' food, that he would not let it come into the house.

Dr. GILBERT wished to say a few words in reply to Mr. Smee's remarks. All sewage grass was very succulent ; every farmer knew that ordinary grass in some years was very succulent, and then it was found advisable to give some dry food along with it. Why, then, not give it with the succulent sewage grass? When the fields were irrigated with sewage, the amount of milk per acre was increased four or five times.

Mr. A. H. SMEE, in reply, said that he looked upon sewage grass as the only way of getting rid of the sewage, but he found that the dairymen round about him never used it if they could help it, for it made the butter rank. The grass, he learned, was sent up to London to be sold as green meat.

The PRESIDENT, in thanking the author, said he did not think that the opinions of Dr. Gilbert and Mr. Smee differed so greatly as might at first sight appear.

Mr. W. H. DEERING then read a paper "On some points in the Examination of Waters by the Ammonia Method." He found that the intensity of colour produced by the Nessler solution went on increasing, and had not come to a stop in ten minutes, the increase being, perhaps, more readily perceived with the paler than with the darker tints. In order to obviate this difficulty, the author, after adding the Nessler to the distillate, and allowing it to stand ten minutes, prepares a caramel solution of the same tint, and compares this with the trial solution of ammonium chloride, which is also allowed to stand ten minutes. He also finds it is necessary to make a correction for the trace of ammonia remaining even in the purest attainable distilled water, and for the alkaline permanganate solution, which should be boiled for a long time, as commercial stick potash gives much ammonia when distilled with water. An important fact, also, is that peaty waters give much ammonia by distillation with sodium carbonate, and much, also, on the subsequent distillation with permanganate solution, which, unless caution be used, might be regarded as evidence of sewage contamination.

The PRESIDENT drew especial attention to the fact that peaty matters existing in potable matters interferes considerably with the indications given by this test. This was a point of very great importance.

Mr. W. THORP said he had not experienced the difficulties in the use of the Nessler test mentioned by Mr. Deering. He found that, when he began, he could only obtain results accurate within 5 or 6 per cent, but that after a few months he could trust them to within 2 or 2 per cent, and he had never found anyone who could judge nearer than that: it was therefore not of much practical use to endeavour to eliminate these very small sources of error. If the nitrogen in peat waters were estimated by the combustion process, it would be found that the carbon was large in proportion to the nitrogen, as compared with sewage contamination.

Mr. HARTLEY said that, in employing the Nessler test in places where other work was being done, it was very necessary to keep the cylinders closed during the distil

234

lation, although there might be no odour of ammonia in the room, otherwise erroneous results would be obtained.

Dr. RUSSELL could confirm Mr. Deering's observations on peaty water, for he had collected some on Dartmoor which contained some ammonia as salts and a considerable amount of albumenoid ammonia.

Mr. DEERING, in reply, said he quite agreed with Mr. Thorp, that the Nessler test was comparatively inaccurate, from there being only about fifteen colour factors which the eye could distinguish. He appeared to have somewhat misunderstood the object of the caramel solution, which was not to get a caramel standard, but to serve as a comparatively unalterable point of comparison for the solution to be examined and the Nessler.

The PRESIDENT, in thanking the author, said he agreed with Mr. Thorp that the combustion method in some cases possessed considerable advantages over the Nessler

test.

The last paper was "On some Nova Scotian Triassic Trap Minerals," by Professor H. Howe. He gives an account of centrallassite, stilbite, sphærostilbite, magnetite, and magnetic hæmatite. The first-mentioned mineral, although closely corresponding, in constituents and apparent quantitative composition, with okenite and gyrolite, is merely related to them, closely indeed, but the merging of one into either of the others as a species is inadmissible.

After thanking the author in the name of the Society, the PRESIDENT adjourned the meeting until Thursday, June 3, for which a large number of papers are announced: (1) "On the Agricultural Chemistry of the Tea Plantations of India," by Dr. C. Brown; (2) "On the Effects of Pressure and Cold upon the Gaseous Products of the Distillation of Carbonaceous Shales," by Mr. J. J. Coleman; (3) “On the Structure and Composition of Pseudomorphic Crystals having the form of Orthoclase," by Mr. J. A. Phillips; (4) "On Nitrosyl Bromide, and on Sulphur Bromide," by Mr. M. M. P. Muir; (5) "On the Action of Chlorine on Pyrogallol," by Dr. J. Stenhouse and Mr. C. E. Groves; (6) "On some New Derivatives of Alizarin," by Mr. W. H. Perkin; (7) "On some Metallic Derivatives of Coumarin," by Mr. Williamson; and several other communications.

PHYSICAL SOCIETY. May 22, 1875.

Professor GLADSTONE, F.R.S., President, in the Chair. THE names of the following candidates for election were read for the first time :-The Lord Lindsay, F.R.S.; Sir W. Thomson, F.R.S.; and Prof. Sylvester, M.A., F.R.S. Mr. SPOTTISWOODE, F.R.S., exhibited and described a "Revolving Polariscope." A luminous beam passes from a small circular hole in a diaphragm through a polariscope, the analyser of which is a double image prism, the size of the hole being so arranged that the two luminous discs shall be clear of each other. If the prism be made to revolve rapidly, one of the discs revolves round the other, and is merged into a ring of light, which is interrupted at opposite sides by a dark shaded band, the position of which depends upon the position of the original plane of polarisation. The discs may be coloured by inserting a selenite plate, and the rapid revolution of the analyser then gives alternating segments of complementary colours; or, if a quartz plate be used, the rotating disc passes successively, twice in a revolution, through all the colours of the spectrum, and when the revolution is rapid merges into a prismatic ring. The effect of the interposition of a -undulation plate, which converts plane into circularly polarised light, was then shown, and Mr. Spottiswoode also interposed a concave plate of quartz, and exhibited the effect of rotation on the characteristic rings of quartz.

Prof. ADAMS, F.R.S., exhibited a polariscope, adapted for showing the optic axes of a crystal in which they are

CHEMICAL NEWS, May 28, 1875.

much inclined to each other, as is the case in topaz. The part of the instrument by which this is effected consists of a frame in which the crystal is supported between two hemispherical lenses, the common centre of which is at the centre of the crystal. The frame is capable of motion round an axis at right angles to that of the instrument. By this means each of the axes can be brought under the cross wires, and the space through which the frame is moved affords a means of determining the angle between the axes of the crystal. The crystal may be immersed in a liquid, the cases in which its optic axes are too far apart to be seen in air.

Dr. MILLS made a verbal communication on "FusionPoint and Thermometry." His apparatus for fusion-points consisted essentially of a beaker, in which stood an inverted funnel, the shortened stem of which carried a test-tube, supported by a contraction at its base. The test-tube contains naphtha of high boiling-point, and the thermo meter and capillary tube containing the substance occupy its centre; the funnel has four equidistant semicircular cuts at the end of its stem, and six on its lips: the beaker is nearly filled with strong oil of vitriol, and has a wooden cover. On the application of heat below the beaker warm oil of vitriol ascends in the funnel, and, cold oil of vitriol descending, enters at the lips. Thus an automatic stirring is kept up, and the mercury in the thermometer rises so regularly as to appear perfectly continuous in course, even under considerable magnifying power. The manner of preparing and filling the capillary tubes was described. Attention was then drawn to the zero error" of thermometry. In thermometers which have not been much used, the zero error must always be determined immediately after experiment. It is also generally necessary to correct for the projection of the thermometer beyond its bath. This correction had been experimentally determined by the author, and required from 1500 to 2000 observations of temperature for each of four instruments used. It was ascertained that the well-known expression, C=0'0001545(T-)N, given by Regnault and Kopp is not supported by actual trial. If we write the expression thus:-C=x(T-)N, experiment shows that x depends on the length N exposed, and x=a+ẞN. For lengths of about 25°, x is about 0.00013, and increases about o'oooor for every additional 25°. The exact values of a and ẞ require, however, to be ascertained for each instrument.

66

Mr. BAUERMAN, F.G.S., described and illustrated a very simple method for ascertaining the electric conductivity of various forms of carbon. The method which was originally devised by Dr. Von Kobell, consists in holding a fragment of the substance to be tested with a strip of zinc bent in a U-form, and immersing it in a solution of copper sulphate. In the case of a bad conductor, a deposit of copper takes place solely on the surface of the zinc; but when a good conductor is employed, a zinc-carbon couple is formed, and a deposit takes place on the surface of the carbon. Numerous specimens were exhibited, which showed that the conducting power is greatest in coal which has been subjected to a great degree of heat, and the lowest temperature at which this change takes place appears, in the case of anthracite, to be between the melting-points of zinc and silver. Such experiments appear to be specially important, as giving a clue to the temperature at which anthracitic metamorphism has been effected by the intrusion of igneous rock.

Prof. WOODWARD exhibited an apparatus for building up model cones and craters. It consists of a wooden trough about 18 inches long with sloping sides; at the bottom of the trough a bladed screw carries forward the ashes, sawdust, or other material used, to an opening through which air from a powerful bellows is forced upwards. A board, 3 or 4 feet square, with a hole in the centre, is placed over the air-jet, and on this the crater is formed. Several of the peculiarities of natural cones may thus be illustrated, and their structures shown by using sawdust of various colours.