Encyclopædia Britannica: or, A dictionary of arts and sciences, compiled by a society of gentlemen in Scotland [ed. by W. Smellie]. Suppl. to the 3rd. ed., by G. Gleig

Component this clafs of animals are, fhells, mother of pearl, and pearl.

Parts of Animal Subftances.

2883 Shells.

2884 Mother of pearl.

2885

Pearl.

2886

Zoophytes.

1. Shells. Such as have been particularly examined by Mr Hatchett, are divided into two claffes. In the one he includes those which have the appearance of porcelain, and have an enamelled furface, which he calls porcellaneous fhells. Such are the various fpecies of voluta and cypræa. Thefe fhells were found by analysis to be compofed of carbonate of lime, with a fmall portion of animal gluten.

2. Mother of pearl.-The second clafs comprehends thofe which are generally covered with a strong epidermis, under which is the fhell, compofed chiefly of the fubftance called nacre, or mother of pearl. Such are the oyster, the river mussel, the baliotis iris, and the turbo olearius. In thefe the proportion of carbonate of lime is fmaller, and that of the animal matter, greater. 3. Pearl. This is a concretion formed in feveral fpecies of fhells, as in fome fpecies of the oyiter and the muffel. It is confidered by fome as a morbid concretion, owing to an excess of the fhelly matter, or to a wound of the fhell containing the animal. Pearls are of a filvery or bluish-white colour, iridescent and brilliant. The refraction of the light is afcribed to the lamellated structure, for they confift of concentric layers of carbonate of lime and membrane alternately arranged. The conftituent parts of pearl are the fame as mother of pearl.

VII. Subftances peculiar to Zoophytes.

The zoophytes, many of which have been examined by Mr Hatchett, are compofed of carbonate of lime, phofphate of lime, and animal matter of different de

Animal

grees of confiftency. In fome the conftituents are on- Component ly carbonate of lime and a gelatinous matter. Such Parts of are fome fpecies of the madrepore, as the madrepora Subftances. muricata, virginea, and labyrinthica; fome fpecies of millepore, as the millepora cerulea and alcicornis, and the tubipora mufica. Others again are compofed of carbonate of lime and a membranaceous fubftance. Such are the madrepora fafcicularis, the millepora cellulofa and fafcialis, and the iris hippuris. White coral and articulated coralline are compofed of fimilar fubftances. Another divifion of zoophytes are compofed of carbonate of lime, a small portion of phosphate of lime, and membrane. Such are the madrepora polymorpha, the gorgonia nobilis or red coral, and the gor. gonia fetofa; but fome of the zoophytes are alfo found to confift chiefly of animal matter, with scarcely any portion of earthy fubftance. To this divifion belong fome fpecies of gorgonia, and many fpecies of fponge.

CHAP. XX. Of Arts and Manufactures.

In this chapter it was intended to give a general view of the application of the principles of chemistry to different arts and manufactures, fuch as the manufacture of foap, of glass and porcelain; the arts of dyeing, bleaching and tanning. In this view it was propofed to explain the principles of thefe arts and manufactures, fo far as they depend on chemistry, leaving the detail to the different treatises on thofe fubjects in. the courfe of the work. But the unavoidable length to which this article has extended, obliges us to refer our readers for the whole to the different treatises.

2887 Analysis of the ochroites.

APPENDIX.

AFTER the chapter on earths was printed off, we received the account of a new earth discovered by Klaproth.

Of Ochroit. This earth was difcovered in a mineral to which Klaproth has given the name of ochroites, of which the external characters are the following:

1. The colour of this mineral is between carmoifin red, clove-brown, and reddish-brown. It is compact, breaks fplintering in irregular but not very sharp or angular pieces. It is perfectly opaque, the powder is reddish-gray; it is not very hard, but brittle. The fpecific gravity is 4.60. This mineral is found in the mine of Bafnætes, near Riddarhytta in Westmannland.

A. "a. A piece of the mineral, after having been ignited to redness, loft two per cent. Its reddish colour had been changed to brown. Its figure had fuffered no alteration.

was reddish gray, and brittle. On being diffufed through water, as ufual, the obtained folution was colourlefs. It remained perfectly tranfparent; a proof that it did not contain tungsten oxide; nitrate of filver, mercury, lead, barytes, &c. proved the abfence of acids.

b. The infoluble refidue of the laft procefs was boiled in nitro-muriatic acid, the filiceous earth being feparated, the folution was decompofed by potash, and the whole boiled for fome time. The alkaline fluid after being neutralized with muriatic acid, and then mingled with carbonate of potash, fuffered no change.

C. a. Two hundred grains of the finely pulverized mineral, were firft boiled in two ounces of muriatic acid, to which half an ounce of nitric acid was gradually added, and the digeftion continued for fome time. The whole became thus diffolved except the filex contained in the mineral. Its quantity amounted to 68 grains.

b. To the folution obtained in the laft procefs, carbonate of ammonia was added fo long, till no permanent precipitate was produced. On letting fall into it fuccinate of ammonia, a curdly precipitate fell, which vanished again on agitation, leaving merely a pale red 5 E 2 precipitate

Ochroit precipitate of fuccinate of iron. This being collected, washed, dried, and strongly ignited, yielded nine grains of oxide of iron.

2888 Peculiar earth.

2889 Ochroit

c. The fluid thus freed from iron, and now colourlefs, was decompofed by carbonate of ammonia. The precipitate obtained was white, and weighed 168 grains; on being deprived of water and carbonic acid by heat, its white colour changed to cinnamon-brown. weighed 109 grains.

d. All the water employed for washing the different precipitates were mingled, evaporated to drynefs, and the ammoniacal falt volatilized; a minute quantity of a muriate was obtained, the bafis of which could not be determined.

From what follows it will become evident, that the cinnamon-brown precipitate (c.) which forms the principal part of the foffil, is a peculiar earth, diftinét from all the others hitherto known. The characteristic property which it poffeffes of acquiring a light-brown colour after being heated, has induced me to call it ochroit earth (A), which may alfo ferve for the mineral

Characteristic Properties of Ochroit Earth.

1. Ochroit earth is capable of combining with car. earth com- bonic acid during its precipitation from acids by carbines with bonated alkalies, and ftrongly confolidating a portion

carbonic

acid.

of water.

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2. Ochroit earth, after being freed from carbonic acid and water, by heat, always appears in the form of a cinnamon-brown powder. The intensity of the colour is in proportion to the heat applied. This colour is not owing to the presence of iron, or manganefe, &c. but it is a characteristic property of the earth.

3. Ochroit earth included in a charcoal crucible, and exposed to the heat of the porcelain furnace, fuffered no change whatever.

4. Urged by the blow-pipe, it becomes phosphoref

cent; fufed with phosphate of foda and ammonia, Ochroit it becomes tinged by it, without effecting a folution of the earth. The falt acquires merely a marbled lemonyellow colour. Borax has likewife no chemical effect upon it. This falt only effects a mechanical division. The earth always appears diffufed through the borax in minute flocculi.

5. Ochroit earth mixed in different proportions with proper fluxes, and applied for painting of porcelain, proved unfuccefful. The painted articles were lightbrown, but the colour was not uniform; a proof that no combination had been effected.

6. Ochroit earth combined with carbonic acid is eafily foluble with effervefcence in acids. The tafte of the folution is very rough and aftringent. The concentrated folution is of an amethyst-red colour; diluted with water, it becomes colourlefs. Ignited ochroit earth, on the contrary, is difficultly foluble in acids in the cold; if nitric acid be employed, the folution is yellowish red.

7. The combination of ochroit earth with fulphuric acid, is cryftallizable. The figure of the cryftals formed in the mafs of the fluid is the octahedron. They are heavy, of a pale-amethyst colour, and difficultly foluble in water; but the fulphate of ochroit, with excefs of acid, is more foluble; the figure of the cryftals formed on the fides of the veffel, is needle-shaped, radiating from a centre. They are more foluble than the former.

8. If a folution of fulphate of foda be mingled with a folution of muriate or nitrate of ochroit, a mutual decompofition takes place. A white infoluble precipitate is formed, confifting of fulphuric acid united to the ochroit earth. This combination may be decompofed by boiling it with double its weight of carbonate of foda. By this means ochroit earth may be obtained

very pure.

9. Ochroit earth is likewife foluble in fulphurous acid, the folution crystallizes in needles of a pale amethyft colour.

10. Muriatic acid diffolves ochroit earth, and yields cryftals, the figure of which is the prifm. It is folu ble in alcohol without imparting to its flame any par ticular colour.

12. Acetite of ochroit could not be crystallized, but yielded an adhesive mafs.

13. Nitrate and muriate of ochroit are decompofable by carbonated earths and alkalies, the precipitate is milk-white. Alkalies and earths freed from carbonic acid, occafion a yellowish-gray precipitate.

14. Prufliate of potash precipitates ochroit from all its neutral folutions, milk-white. The precipitate is foluble in muriatic and nitric acid (B).

15. Tincture of galls occafions no change in the folutions of this earth.

16. Hydroguretted hydrofulphuret of ammonia precipitates the folution of ochroit earth, yellowish white. 17. Water impregnated with fulphurated hydrogen occafions no change in the folutions of ochroit earth. 18. Succinates precipitate ochroit earth white. 19. Phosphate

(4) From the Greek word wxgos, (flavefcens), brownish-yellow.

(B) If the earth contained the muriates and quality of iron, it becomes by this means manifefted.

Ochroit

Earth.

19. Phosphate of foda occafions in the folutions of this earth a white precipitate, which again vanishes by the addition of nitric or muriatic acid.

20. Tartrites of potash alfo precipitate this earth white.

21. Oxalates effect a like decompofition, the oxalate of ochroit, however, is not foluble in nitric or muriatic acids.

22. Alkalies and alkaline carbonates do not act on ochroit earth.

23. Ammonia feebly acts on it, under certain circumstances, as may be evinced from the following experiment:

A folution of nitrate of ochroit, prepared by dif folving 100 grains of carbonate of ochroit (not abfolutely free from iron,) in nitric acid, was decompofed by carbonate of ammonia, and digefted in the fluid, containing a confiderable quantity of carbonate of ammonia in excefs, for fome days. The fluid which had acquired a yellow colour, was feparated and neutralized by fulphuric acid, and then fet in a warm place. A gray precipitate was thus obtained, which,

2890

characters

"From what has been stated, it becomes obvious, that General rethe ochroit earth bears the nearest relation to yttria; marks and for, like this, it forms a connecting link between the of the ochearths and the metallic oxides. Like yttria, it has roit earth. the property of forming a reddish coloured falt with fulphuric acid, and is precipitable by prufliate of potafh; but differs from yttria, that it does not form fweet falts, that it is not (at least very fparingly) foluble in carbonate of ammonia; and that, when ignited, it acquired a cinnamon-brown colour. farther differs from yttria by not being foluble in borax or phosphate of foda when urged upon charcoal before the blow-pipe, which falts eafily effect a folution of yttria, and melt with it also into a pellucid pearl" *.

*Nichol. Your. viii. P. 212.

ERRATA in CHEMISTRY.

P.483. 1. 22. col. 1 ft. For Berthollet read Bartholdi. P.508. 1. 10. col. 2d. It is faid that Mr Keir found that fulphuric acid froze at 45° Fahrenheit. This is only inferred from the thermometer being

Plate CXLII.

ftationary at 45° during the melting of the frozen acid. A greater degree of cold was always found neceflary for its congelation. Phil. Tranf. 1787. p. 279.

EXPLANATION of the PLATES.

Fig. 1. Reprefents Harrison's pendulum conftructed on the principle of the unequal expanfion of metals. Fig. 2. The calorimeter of Lavoisier and Laplace, fee page 476.

Fig. 3. Iron bottle and bent gun-barrel for procuring oxygen gas from manganefe. The black oxide is reduced to powder, and introduced into the bottle A. The bent tube is put on the mouth of the bottle at C, and luted with the materials defcribed at the foot of page 490. The bottle is then expofed to a red heat, and the gas which comes over is received in jars on the pneumatic apparatus.

Fig. III. and 4. reprefent the apparatus for the decompofition of water. See page 496.

Fig. 5. Pneumatic trough for collecting gafeous bodies. Suppofe a quantity of fulphurated hydrogen gas is to be collected, which is described in page 505. The iron filings and fulphur which were melted together in a crucible, and which then form a black brittle mafs, are to be introduced into the glass veffels. Fig. 6. B is a bent tube ground to fit the mouth D, and is air-tight. To the other mouth C is fitted the ground ftopper A. One end of the bent tube is fitted into the mouth D, and the other placed under the glass jar Fon the fhelf of the pneumatic trough E, which is filled with water about an inch above the furface of the fhelf. The jar is alfo previoufly filled with water, cautiously inverted, and fet on the fhelf. The apparatus

being thus adjufted, muriatic acid is poured into the opening C, and the ground ftopper is immediately replaced. A violent effervefcence takes place, a great quantity of gas is difengaged, and as there is no other way for it to escape it paffes into the glass jar. When this is filled, it is removed to another part of the fhelf; another jar which was previously filled with water is put into its place, and fo on till the whole gas is collected.

Fig. 7. Papin's digefter. A is the body of the veffel, which has been generally made of copper or iron,. very thick and strong. BB are two ftrong bars fixed to the fides of the veffel. To the upper end of these bars is fixed the cross bar C, through which paffes a ftrong fcrew D, which preffes on the lid of the veffel at E, fo that it is enabled to refift the elastic force of the vapour; and the water can thus be raifed to a higher temperature than the ordinary boiling point.

Fig. 8. This represents an apparatus for distillation. A is the furnace, B is the body of the ftill, which is generally made of copper; C is the top or head, made of the fame metal. The vapour as it rises from the liquid by the application of heat, paffes along the tube D, which communicates with a spiral tube in the refrigeratory E, which being filled with cold. water, the vapour is condenfed, and paffes out at the other extremity of the tube F, and is received in the veffel G.

Plate

Explanation

of Plates.

Plate CXLIII.

Fig. 9. Glafs Retort.
Fig. 10. Tubulated retort.
Fig. 11. Glafs Alembic.
Fig. 12. Solution glass.
Fig. 13. Crucible.

Fig. 14. Apparatus for obtaining muriatic acid from muriate of foda by fulphuric acid. The muriate of foda is introduced into the retort A, and by means of the bent tube B the fulphuric acid is added. The ma. trafs C is adapted to the retort, to receive the portion of impure fulphuric acid and muriatic acid which paffes over towards the end of the operation. D, E, and F, are bottles containing water; the quantity of which fhould be equal in weight to that of the falt employed. These bottles are furnished with tubes of safety GG; or the tube of fafety may be applied as H in the bottle E.

Fig. 15. Apparatus for impregnating fluids with gafes. A is a tubulated retort which is joined to B, a tubulated receiver, from which a bent tube C paffes to the fecond receiver D. This laft communicates with the bottle F by means of the bent tube E. The end of the tube C which enters the receiver D, is furnished with a

valve which prevents the return of any gas from the Explanation receiver D to the receiver B, in cafe a vacuum fhould of Plates. take place in the courfe of the operation in the receiver B, or in the retort A. The gas which is not abforbed by the water in the receiver D, paffes through the tube E to the bottle F.

Fig. 16. A gazometer, which is a convenient ap paratus for holding gafes. It is ufually made of tin plate. A is an inverted veffel, which exactly fits another, which is fixed within the cylinder B. When it is preffed down to the bottom of the cylinder, water is poured in, by which means the fmall quantity of air which remains in the intermediate spaces, is forced out, and the gas to be preferved may be introduced at the lower ftop-cock C. The vessel A is nearly balanced by the weights DD, which are connected with it by means of the cords a a a a, which move on the pullies bbbb. As the gas enters the apparatus, it forces up the veffel A, and in this way it may be completely filled. It is forced out by turning the ftop-cock E, and preffing down the veffel A, and may be conveyed into a pneumatic apparatus, and received in jars by means of the flexible tube F.