scholarly journals XLIII.—On Circular Crystals

1853 ◽  
Vol 20 (4) ◽  
pp. 607-623 ◽  
Author(s):  
David Brewster
Keyword(s):  
Phosphoric Acid ◽  
Royal Society ◽  
Field Of View ◽  
Single Individual ◽  
Optical Contact ◽  
Optical Phenomena

In 1836, Mr Fox Talbot communicated to the Royal Society a paper “On the Optical Phenomena of certain Crystals” which he obtained by dissolving a crystal of Borax in a drop of somewhat diluted Phosphoric acid. When the acid and the salt are in proper proportions, “the field of view of the microscope is seen covered with minute circular spots, each of which is like a tuft of silk radiating from a centre, and is composed of a close assemblage of delicate acicular crystals forming a star.” Among these crystals are seen interspersed “a number of circular transparent bodies, which are tufts or stars of acicular crystals, in such close assemblage as to be in optical contact with each other, and to produce the appearance of a single individual.”

On the optical phenomena of certain crystals

1837 ◽  
Vol 3 ◽  
pp. 388-390
Keyword(s):  
Optical Properties ◽  
Phosphoric Acid ◽  
Crystalline Lens ◽  
Field Of View ◽  
Optical Contact ◽  
Circular Area ◽  
Black Cross ◽  
Optical Phenomena ◽  
The Cross ◽  
Innermost Ring

In this memoir the author gives an account of the optical properties of certain minute crystals, obtained by the evaporation of a solution of borax in phosphoric acid, exhibited when they are examined by means of the polarizing microscope. The field of view is then seen covered with minute circular spots, each composed of a close assemblage of delicate acicular crystals, radiating from the centre ; together with other circular bodies, in which this disposition is not observable, on account of the close union of the component crystals, which, producing optical contact, gives perfect transparency to the whole mass. When the field of view is rendered dark by the rectangular crossing of the polarizing laminæ, each of these little circles becomes luminous, and exhibits a well-defined dark cross, dividing its area into four equal sectors. These crosses have a similar position in all the circles ; and their direction remains unaltered when the crystals are turned round in their own plane, by causing the plate of glass, on which they are placed, to revolve. On examining the larger circles with a high magnifying power, and under favourable circumstances of illumination, the author observed upon each a series of coloured concentric rings : but the number as well as the colour of these rings varies in different crystals. The innermost ring is deeply coloured, or black ; and incloses a central space of white light, which is traversed by the arms of the cross, intersecting in the centre. This part of the cross, which stands within the innermost ring, is beautifully defined, and perfectly black. The whole system of phenomena are exactly analogous to that exhibited by uniaxal crystals ; and corresponds still more closely with those discovered by Sir David Brewster in spheres of glass, the density of which had been rendered variable from the centre to the surface by immersion in heated oil ; excepting that the miscroscopic crystals here described are possessed of a far more intense polarizing energy. The author thinks it probable that the phenomena are in both cases produced by similar conditions of density ; which, in a circular mass formed by the aggregation of needle-shaped crystals radiating from a common centre, it is natural to suppose would rapidly increase from the circumference to the centre. By watching the progress of crystallization he ascertained that this was, in fact, the mode in which the crystals are constructed ; for they frequently appeared, at first, in the form of lengthened prisms, which subdivided themselves at both ends into an immense multitude of divergent fibres, like those of a brush ; apparently repelling each other as they extended in length, and occupying spaces corresponding to two opposite sectors of a circle ; until, by spreading still farther in breadth, their edges united, and filled the whole of a circular area. In all the stages of this process, the formation of the black cross may be seen to keep pace with the developement of the crystal, until perfectly displayed on the completion of the crystalline structure. The author notices the analogy which this structure presents with that of the crystalline lens of the cod fish, as has been lately described by Sir David Brewster ; and also the remarkable correspondence existing between the optical properties resulting from this structure, and the phenomena of the circular polarization of fluids, which have been accounted for by the existence of molecules of a structure nearly similar.

III. On the optical phenomena of certain crystals

1837 ◽  
Vol 127 ◽  
pp. 25-27 ◽  
Keyword(s):  
Internal Structure ◽  
Royal Society ◽  
Polarizing Microscope ◽  
Optical Phenomena

Some time ago I had the honour to communicate to the Royal Society an account of my invention of the polarizing microscope. This instrument possesses so great a power of developing the internal structure of transparent bodies, even in their mi­nutest visible particles, that I feel confident the employment of it will lead to many new and interesting results. At present I mean to confine myself to the description of a phenomenon which shows strikingly the beautiful order and regularity with which nature disposes the fabric of some of her minutest visible works. The object I speak of is a kind of minute crystallization which may be obtained in peculiar circumstances, and I doubt not, in many different ways; but the manner in which it has presented itself to my observation is as follows.

scholarly journals XVI.—On the Solubility of Fluoride of Calcium in Water, and its relation to the occurrence of Fluorine in Minerals, and in Recent and Fossil Plants and Animals

1846 ◽  
Vol 16 (2) ◽  
pp. 145-164 ◽  
Author(s):  
George Wilson
Keyword(s):  
New Zealand ◽  
Chemical Composition ◽  
Phosphoric Acid ◽  
Royal Society ◽  
Fossil Plants ◽  
Zoological Society ◽  
Animal Remains ◽  
The Matrix ◽  
Fossil Bones

The investigation I am about to bring before the Royal Society, was undertaken in consequence of a discussion which took place in the Zoological Society of London in 1843, in reference to the chemical composition of the bones of the gigantic bird the Dinornis, discovered some time previously in New Zealand. At the meeting in question, the distinguished palæontologist Dr Falconer drew attention to the frequent, if not constant, occurrence of fluoride of calcium in fossil bones, and, as he stated, also in those of mummies; and threw out the suggestion, that the fluoride might shew itself in these animal remains, not as an original ingredient of the bones, or as derived from the matrix in which they were found, but as a product of the transmutation of their phosphate of lime. The idea of such a conversion taking place, is as old at least as the days of Klaproth, who suggested the possibility of phosphoric acid becoming changed into fluoric. It is commented upon by Fourcroy and Vauquelin, as well as by Gay Lussac, as a thing possible but not probable, and which their ignorance of the nature of fluoric acid prevented them from discussing satisfactorily.

scholarly journals V. On the modifications of the spectrum of potassium which are effected by the presence of phosphoric acid, and on the inorganic bases and salts which are found in combination with educts of the brain

1880 ◽  
Vol 30 (200-205) ◽  
pp. 278-286 ◽  
Keyword(s):  
Nitric Acid ◽  
Phosphoric Acid ◽  
Royal Society ◽  
Potassium Salt ◽  
Extraction Process ◽  
Dilute Solution ◽  
Metaphosphoric Acid ◽  
Quantitative Analyses ◽  
The Subject ◽  
The Brain

Among the results of a large investigation on which I have for many years been engaged in regard of the chemistry of the brain, I had been led to conclude that the so-called “ protagon” of Oscar Liebreich is not a definite chemical body, but is a variable mixture of several bodies. This conclusion of mine (which agrees with opinions expressed on the same subject by Strecker, Diaconow, and HoppeSeyler) was published by me in 1874, and endeavours to controvert it have since then been made, on several occasions, by Dr. Arthur Gamgee. Last summer, he brought before the Royal Society his contentions for the chemical individuality of “protagon”; and it fortunately was in my power shortly afterwards to publish evidence, which, I believe, those who will take the trouble to follow it will find quite unanswerable, that Dr. Gamgee’s contentions were mistaken.§ Part of my evidence to that effect consisted in showing by quantitative analyses that Dr. Gamgee’s so-called “ protagon” contains 0·7 per cent, of potassium; secondly, that in connexion with trifling differences in the extraction process, the proportion of potassium in different specimens of “protagon” can be made to range from a trace to 1·6 per cent.; thirdly, that with the variable quantities of potassium the quantities of phosphorus and other ingredients will also vary. In the last published number, No. 200, p. 111, of the “Proceedings of the Royal Society,” I find that Dr. Gamgee has recently brought the question again under notice of the Society, and that, in doing so, he especially rests his case upon the following statement made by his colleague, Professor Roscoe, on the subject of some examinations, which, at Dr. Gamgee’s request, he had made for him: see “ Proceedings,” vol. xxx, p. 113:—“I have examined spectroscopically for potash a sample of protagon furnished me by Dr. Gamgee, and labelled ‘Protagon, twice recrystallised, Blankenhom.’ I could not detect any potash by the spectroscope in the incinerated mass from 0·1 grm. of substance. With the carbonised mass obtained from 1·0 grm. of substance I obtained the potasssium line ( α ) very faintly, and from comparative experiments with a dilute solution of a potassium salt I estimate the quantity of potash in 1 grm. of the substance Lot to exceed 1/20 mgrm. The carbonised residue of 1 grm. of protagon was carefully oxidised with pure nitric acid, when a small quantity of fused metaphosphoric acid remained after ignition. The residue weighed 0·0278 grm., corresponding to 1·08 per cent, of phosphorus.— (Signed) H. E. Roscoe.”

scholarly journals On Circular Crystals.

1857 ◽  
Vol 3 ◽  
pp. 183-188
Author(s):  
David Brewster
Keyword(s):  
Phosphoric Acid ◽  
Polarized Light ◽  
Optical Contact ◽  
Ordinary Light ◽  
Black Cross ◽  
The Cross

The author, after mentioning Mr Fox Talbot's observation, in 1836, of circular crystals from a solution of borax in phosphoric acid, stated, that about twenty years before Mr Talbot's paper was published, he had obtained circular crystals from oil of mace, and from a mixture of that oil with tallow or rosin. These circular crystals are groups of radiating prisms, in optical contact, so as to appear like individual crystals. Viewed by polarized light, they exhibit four luminous sectors, separated by a rectangular black cross, which often has its arms so divergent, as to form four dark sectors. The arms of the cross are parallel and perpendicular to the plane of primitive polarization. When a bright disc of ordinary light was looked at through these circular spots, there was seen a halo, or two halos, produced by the crystals of the oil of mace.

scholarly journals Optical Phenomena in Turbidimetric Analysis Applied to Sulfate Determination in Phosphoric Acid.

1960 ◽  
Vol 14 ◽  
pp. 1279-1287 ◽  
Author(s):  
Sven-Eric Dahlgren ◽  
James N. Shoolery ◽  
S. Rundqvist ◽  
E. Varde ◽  
Gertrud Westin
Keyword(s):  
Phosphoric Acid ◽  
Optical Phenomena ◽  
Turbidimetric Analysis ◽  
Sulfate Determination

scholarly journals XVII. New experiments on some of the combinations of phosphorus

1818 ◽  
Vol 108 ◽  
pp. 316-337
Keyword(s):  
Phosphoric Acid ◽  
Royal Society ◽  
Phosphorous Acid

In a paper published in the Transactions of the Royal Society, for 1812, I have detailed a number of experiments on phosphorus, from which I deduced the composition of some of its compounds with oxygen, with hydrogen, and with chlorine. Since the appearance of this paper, various researches have been brought forward on the same subject, in which some results, differing very much from each other, and from mine, are stated. I ventured to conclude that the phosphoric acid contained double the quantity of oxygen to that in the phosphorous acid; and that phosphoric acid contained about 3/5 of its weight of oxygen. M. Berzelius considers the oxygen in phosphoric acid to be 128.17, and M. Dulong, 124.5, the phosphorus being 100. M. Dulong and M. Berzelius suppose the quantity of oxygen in phosphorous acid to be to that in phosphoric acid as 3 to 5. The motive which immediately induced me to resume the enquiry respecting the phosphoric combinations, was M. Dulong's paper. This ingenious chemist has not only endeavoured to establish new proportions in the known compounds of phosphorus, but has likewise attempted to prove the existence of two new acids of phosphorus; and has denied several facts which I considered as sufficiently established.

scholarly journals Quantitative X-ray phase contrast waveguide imaging of bacterial endospores

2015 ◽  
Vol 48 (2) ◽  
pp. 464-476 ◽  
Author(s):  
R. N. Wilke ◽  
M. Hoppert ◽  
M. Krenkel ◽  
M. Bartels ◽  
T. Salditt
Keyword(s):  
Phase Contrast ◽  
Phase Retrieval ◽  
Mass Density ◽  
Field Of View ◽  
Large Field ◽  
Single Individual ◽  
X Rays ◽  
Contrast Imaging ◽  
X Ray ◽  
Freeze Dried

Quantitative waveguide-based X-ray phase contrast imaging has been carried out on the level of single, unstained, unsliced and freeze-dried bacterial cells ofBacillus thuringiensisandBacillus subtilisusing hard X-rays of 7.9 keV photon energy. The cells have been prepared in the metabolically dormant state of an endospore. The quantitative phase maps obtained by iterative phase retrieval using a modified hybrid input–output algorithm allow for mass and mass density determinations on the level of single individual endospores but include also large field of view investigations. Additionally, a direct reconstruction based on the contrast transfer function is investigated, and the two approaches are compared. Depending on the field of view and method, a resolution down to 65 nm was achieved at a maximum applied dose of below 5 × 105 Gy. Masses in the range of about ∼110–190 (20) fg for isolated endospores have been obtained.

IV. On the existence of phosphoric acid in rocks of igneous origin

1844 ◽  
Vol 134 ◽  
pp. 53-56
Keyword(s):  
Phosphoric Acid ◽  
Royal Society ◽  
Elementary Body ◽  
Satisfactory Explanation ◽  
Great Resistance ◽  
Igneous Origin ◽  
Mineral Acids ◽  
White Porcelain

The important although obscure functions attributed to the elementary body phosphorus, both in the vegetable and in the animal kingdoms, and the well-known fact that rocks of nearly every description afford on disintegration soils more or less capable of supporting the life of plants, and from which consequently phosphoric acid cannot possibly be absent, seemed to render a search for that substance in rocks of igneous origin generally very desirable, because if there found, an easy and satisfactory explanation of the origin and first source of the element in question would be given. As I am not aware that any direct researches on this subject have yet been made, or at least placed on record, I venture to submit to the notice of the Royal Society the results of a few experiments made by myself, which, so far as they go, resolve the question in the affirmative. The first substance tried was the fine white porcelain-clay of Dartmoor, Devon, the result of the disintegration of the felspar of the granite of that district. This is one of the chief components of porcelain and of the finer kinds of English earthenware, and was found on analysis to correspond very closely in composition with that of the material employed in the manufacture of the Sèvres porcelain. It was thought that phosphoric acid, if present, would be in combination with a portion of the alumina; and as the phosphate of that earth is readily soluble in dilute mineral acids, while the silicate offers great resistance to these agents, mere digestion with acid would suffice to extract the whole, or the greater part of the phosphate, which could be afterwards precipitated by an alkali, and examined.

scholarly journals Further observations on the optical phenomena of crystals

1837 ◽  
Vol 3 ◽  
pp. 455-456
Keyword(s):  
Phosphoric Acid ◽  
Polarized Light ◽  
Gum Arabic ◽  
Mixed Solution ◽  
Polarised Light ◽  
Dark Colour ◽  
Black Cross ◽  
Optical Phenomena ◽  
High Degree ◽  
Great Energy

The author had described, in a former paper, the remarkable cir­cular mode of crystallization frequently occurring from a solution of borax in phosphoric acid, and producing, when examined by the polarising microscope, the appearance of a black cross, with four sectors of light, and occasionally coloured rings, upon each crystal. In the present memoir, he describes some deviations from the usual forms of crystalline circles ; the most striking varieties consisting in the cross being itself highly coloured, instead of black, upon a white ground. The author shows that these crystals consist of boracic acid alone, resulting from the decomposition of the borax by the phosphoric acid. He gives an explanation of the optical ap­pearances they present on the hypothesis of their being constituted by an aggregate of acicular crystals, radiating from a central point; and the whole circle being of variable thickness at different distances from its centre, and acting with great energy on polarised light. Other modes of crystalline formation, dependent chiefly on the Presence or absence of combined water, are next described. These sometimes produce crystals composed of two opposite sectors of a circle, united at the centre; at other times, they exhibit irregular elongated shapes, having a stem, either subdivided at both extremi­ties into minute diverging fibres, or abruptly truncated; and occa­sionally they present regular geometric forms : but, whatever be their shape, they undergo, in general, spontaneous changes in the course of one or two days after they have been formed. The author then notices a property belonging to some crystals, similar to that possessed by the tourmaline, of analysing polarized light; for which reason he denominates them analytic crystals . As an example, he mentions those obtained by dissolving sulphate of chromium and potash in tartaric acid by the aid of heat. A drop of this solution, placed on a plate of glass, soon yields, by evapora­tion, filmy crystals, which frequently have this property. The plumose crystals of boracic acid, when crystallized from a solution of borax in phosphoric acid, also possess this analytic power, and present very beautiful appearances when viewed with the polarizing microscope. Another instance occurs in the oxalate of potash and chromium, a salt whose optical properties have been investigated by Sir David Brewster. If gum arabic be added to a solution of this salt, and a drop of it be put between two plates of glass, a very beautiful arborescent, but microscopic crystallization takes place, composing a multitude of minute prisms, growing, as if by a species of vegetation, and variously arranged in sprigs and branchlets, often resembling in miniature, the tufts of marine confervæ. A similar plumose appearance, accompanied with the same analytic proper­ties, is obtained from the evaporation of a drop of a mixed solution of nitre and gum arabic. This analytic effect is shown to be the consequence of the high degree of doubly refractive power pos­sessed by these crystalline filaments, and which exists even in those whose diameter is evanescent on microscopic examination. The author entertains hopes that it will be possible to obtain large and permanent artificial crystals, which may possess the advantages of the tourmaline, without the inconvenience resulting from its dark colour.

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