melted sulphuret of potassium, which is always whitish grey, whereas the sulphur produced by the other methods has a slight tinge of the yellow, but the chemical constitution of the different sulphurets in solution will sufficiently illustrate this, since, according to theory, the solution of the sulphuret of potassium, procured by melting, is free from hydrosulphurous acid, the decomposition of which cannot be entirely avoided in the solution of the other sulphurets. Yet slight traces of hyposulphite of potassa will still be found in a solution of hepar sulphuris, which is to be ascribed to the oxidizing influence of the atmo spheric air. Amongst other proofs of its existence is this: that after the precipitation of the lac sulphuris under the usual precautions, the supernatant fluid will become turbid from the decomposition of the hyposulphurous acid. Hence it is requisite to separate the precipitate from the supernatant fluid as soon as possible, and to use only so much acid as is necessary to decompose the pentasulphuret without the hyposulphite.

Lac sulphuris heated upon platina, should entirely volatilize any impurity of solid substances will remain behind, and can easily be tested. Boiling water should extract nothing from it, and it should be free from hydrosulphuric acid, the presence of which can be substantiated by mixing it with a solution of acetate of lead.

It is not uncommon to find arsenic in lac sulphuris, arising chiefly from the application of the ordinary hydrochloric acid. To ascertain its presence, the sulphur is to be digested with caustic ammonia, which, with a trace of sulphur, will dissolve the sulphuret of arsenic. After the evaporation of the ammonia, the residue is to be treated with concentrated nitric acid, and the solution, saturated with carbonate of lime, is to be evaporated and ignited the residue again dissolved in hydrochloric acid is to be introduced into Marsh's apparatus, by which the smallest traces of arsenic can be discovered.

Pure lac sulphuris, well lixiviated and dried, will remain unchanged by atmospheric air.

In reference to its chemical constitution, it has been assumed by some Chemists, that it is a hydrate of sulphur; by others, that it differs from flowers of sulphur only in the minuteness of its particles.

The enquiries which I have instituted on the subject, confirm the opinion which I have already entertained, that it is a sulphur of minute division, containing also a small proportion of hydrosulphuric acid, perhaps a persulphuret of hydrogen.

Although every kind of sulphur that I examined, contained a small proportion of hydrosulphuric acid, still lac sulphuris yielded the most, and as this sulphur is often mixed with the

sulphur obtained from a hyposulphite salt, I have ascertained both their quantitative proportions of hydrosulphuric acid. Boiling water will only remove that portion of this acid which adheres mechanically to the sulphur, but not that which is chemically united with it, nor does a solution of acetate of lead indicate its presence, but when the sulphur is melted, the hydrosulphuric acid is discharged. For that purpose I introduced 200 grains of the dry sulphur to be experimented upon, into a small glass retort, and brought the same by connecting tubes in communication with two glass vessels, one containing a solution of chloride of copper, the other a similar solution supersaturated with ammonia. The sulphur was melted and boiled until all gaseous disengagement ceased, when a current of atmospheric air was passed through the vessels, in order to carry every particle of the emitted gas through the solutions of copper. The sulphuret of copper thus obtained was collected upon a small filter, quickly lixiviated, and oxidized by concentrated nitric acid. In this solution the sulphuric acid was precipitated by nitrate of barytes, and from the sulphate of barytes was computed the quantity of hydrosulphuric acid. Thus 100 grains of lac sulphuris gave 0.03939 grains of H, S (hydrosulphuric acid), whereas sulphur obtained from the decomposition of pure hyposulphite of soda contained only 0.01900 grains H, S.

The sulphur obtained from the decomposition of sulphurous acid by hydrosulphuric acid, has the same appearance as that derived from a hyposulphite salt; both acids may meet in a highly diluted state, and the precipitated sulphur may remain suspended in the water for some time, yet where the sulphur is deposited, it will be of a yellow colour. It is the same with sulphur obtained from the decomposition of hydrosulphuric acid by peroxide of iron. The only precipitated sulphur that resembles lac sulphuris, is that derived from the decomposition of an aqueous solution of hydrosulphuric acid gas.

Lac sulphuris represents, under the microscope, an aggregate of small globules, as shown in fig. E, each globule varies, about from to Totoo of an inch in diameter: they appear opaque and smooth, and bear no indication of crystalline structure. The globules of sulphur obtained from hyposulphites show the same this difference, that they remain exposed to the atmospheric air, for a length of time in a semifluid state, whereas those of lac sulphuris, as soon as they are removed

The figure in this plate exhibits various sulphur globules magnified to 400 linear dimensions.

from the menstruum in which they are precipitated, become directly solid. This is the cause why the sulphur of the hyposulphurous acid forms, freshly precipitated, an adhesive mass adhering to the sides of the vessel. The globules stick to each other, and often unite to larger ones, and enclose impurities, such as metallic substances, contained in the fluid from which they have been separated, and from which they are difficult to be freed, but which are detected as soon as the sulphur is dissipated by heat.

Sulphur globules in this semi-fluid state exhibit, under particular circumstances, interesting changes, which I found best illustrated by those of sublimated sulphur.

The flowers of sulphur (sulphur sublimatum), such as they are obtained from manufactories, consist of globules of different sizes, whose diameter varies between 0 and 60 of an inch. They are opaque, and not crystalline, as generally considered, "arising from the opinion that sulphur assumes a crystalline form

in its passage from a state of fusion." To ascertain the cause of this anomaly, I allowed the vapour of boiling sulphur to fall upon a glass slide at different distances from the mouth of the tube, which exhaled the sulphur vapours, and found, under the microscope, that it contained transparent globules of various sizes (See fig. B.) from 70 to 1200 of an inch, and even smaller, according to the distance at which the glass slide had been held; hence the size is dependent on the union of one or more of the small globules,

Fig. B.

so that, if the glass slide is kept very near to the orifice, the globules will unite together. into one mass, as represented in fig. 11. These globules are semi-fluid, which is proved by gently passing a glass rod over them, when they are drawn in long filaments like a resinous substance. This condition of the globules has already been noticed by Frankenheim. (See Poggendorf's Ann. xxxix., p. 376-384.)

Fig. C.

If these globules be kept from the influence of light and left undisturbed, they loose their transparency and become solid, but retain their smooth globular forms, as in fig. C. Thus, they are found in the dark chambers in which the sulphur has been deposited by sublimation.

Fig. F.

But these globules undergo a gradual and interesting change when the glass-slide, upon which the freshly sublimated sulphur has been deposited, is shaken and exposed to light. Several globules unite at first into one, as in fig. D.

They lose at the same time their transparency, their surface becomes rough, and at last unite into larger semi-globular masses as in fig. F.

From these masses are growing out small indistinct crystals, which, after a few days, increase, and become more distinct, whereby those dark points from which the crystals emanated, become lighter. The figures 6, 7, 8, 9, 10 represent, in single large globules, these gradual changes. (Figs. 1, 2, 3, 4, 5, show merely the smallest size of globules).

The whole mass is frequently changed into transparent crystals, whose diameter is often nearly thrice as large as that of their globules, see fig. 12. These crystals are quite transparent and some are perfect, forming an elongated octohedron with a rhomboidal base.

between lac sulphuris and the sulphur obtained from the various other methods.

Royal German Spa, Brighton, Dec. 1842.

Mr. Scholefield observed, in reference to the contamination of hydrochloric acid with arsenic, alluded to by Mr. Schweitzer, that a method had recently been suggested for removing the arsenic; namely, to agitate the acid in contact with a small portion of

Fuller's Pharmacopoeia Extemporanea

Kirkpatrick's Advice with Regard to Health 1768

1740

Jackson on Sympathy

Saunders's Institutes of Therapeutics

Cullen's Nosology

Clarke's Practice of Physic

Miller's Disquisitions in the History of Me-
dicine

Thomson's Elements of Materia Medica and
Therapeutics

The Bengal Dispensatory, Dr. O'Shaughnessey
The Treasure of Evonimus, conteyninge the
Wonderfull Hid Secretes of Nature, touch-
inge the most apte Formes to Prepare and
Destyl Medicines, &c.

;}

Dr. P. H. GREEN.

Mr. C. F. BUCKLE
(Peterborough)

1559

DONATIONS TO THE MUSEUM.

Mr. TAYLOR, New Bridge Street.-Sublimed Indigo.

Mr. BELL.-Soda Sulphas, impure-Ditto, pure.

Mr. G. BENNETT, Newark.-Ten specimens of Minerals.

Messrs. DAVY, MACMURDO & Co.-Acetate of Lead, in fine crystals Nitrate of Potassa, in fine crystals.

Messrs. S. & G. ALLEN, Cowper Street, Finsbury Square.-Specimens of Turkey, Indian, and English Rhubarb, in powder-Essential Oils of Almond, Juniper, Caraway, and Pimento.

APPARATUS.

Messrs. DAVY, MACMURDO & Co.-Table of Chemical Tests, coloured. Mr. WOOLLEY, Regent Street, Westminster.-Case of Hydrometers, complete.