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ed of two four-sided pyramids applied base to base, with thelops truncaled, forming a ten-sided crystal, but perfect crystals are not to be eXpected in preparations of any sali upon alarge scale, and the disposition whicli iis angies silow to the assumption of this form is suffcient. One part is solubie in
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The crystals of subcarbonate os soda, is exposed to air, lose a part of their Water, and emoresce or fati into poWder. Heiace, the proportion os soda contained in the sali hept in the shops becomes indefinite. In this sali completely emoresced, the proportion of Water lost may be nearly one-halfof the whole. By a desinite exposure to heat the wholewater may be eVaporaled, and the sali thus prepared is moreuseful and uniform in many of iis applications. Care musthe taken that the beat be not urged too far, for a red heat deprives it also os iis carbonic acid. Dried subcarbonate offoda contains, according to Κirwan, carbonic acid 40,O , Soda 59,86 ; and IDO paris of the crystals are deprived of their 64 of Water.
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Tahe of the Salt whicli rem alias after thedistillation os muriatic acid, t vo
This preparation depends upon the fame principleg asthose tipon Whlch the sulphate os potass is formed; but soda differs froni potas; in iis relation to sulphuriC acid, and does not Seem to unite with it into a Super-Sali; aS, hoWever, more than half their weight of water enter into the compocltion of the crystals of sulphate of soda, is that water
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be acid it will insuenco the character of the sali, and lienceiis saturation with aikali is as necessary here as in the formerinstance. Iis crystals are siX-si ded prisms terminated by twosided pyramids, but they are most common ly irregular and channelted ora their fides. One part is solubie in someWhat less than three of water at 6O', and in less than iis own bulla at 2l2'. Κirwan gives iis proportions as ac id 23, 52, Sodal , 8, water 58,O0. Ιf heat ed, it melis Dom the agency of iis mater of crystallization, and when this is evaporat ed, it may be fused by an increase of the heat. Aster this toss of Water, Κirwan States it to consist os acid 56, soda 44. In France it has been prepared by disturbing iis more regularcrystalligation by stirring ; When it talaes a sillay spicular form, and has been calle θ' improperly Sal HEpsom. It willhe observed, that besides this process for iis formation, sulphate soda Stands as an article in the catalogue of Materia Medica. The quantity obtained, by the pharmaceutic process forsuppiying muriatic acid, is not sussicient for the consumption ; and there ro it has been judged right to admit it also
rom the manufacturers, Who Prepare large quantities, especialty in the works for muriate os ammonia, Where they Ob-tain a very impure subcarbonate os ammonia in their frst distillation os bones, and separate these impurities by sulphuricacid; they afterWards employ a doubie decomposition, miX-ing the sulphate os ammonia with muriate of soda; Dom this they sublime the muriate os ammonia, when the sulphate offoda remains, whicli, is it be crystalli et ed, is sussiciently pure and very cheaP.
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Ordinary alum sonaetimes appears to contain ammonia 28weli as potass, but not so uniformiy, or in such quantity, asto affect iis application to medicine ; and Vauquelin . de C m. V. 50.ὶ having examined various foris Doni different countries, gives the following as the usual proportions in I 00,OO paris: acid 30,52, alumine 10,50, potasS IO,lo, Water 48,58. Iis crystals contain ' 44 of Water, and when exposed to heat they meli, and the Water evaporateS away; this is the object of the present preparation, Whicli is intend-ed for external use. It should be remembered in preparingit, that a violent heat Nili decompose the sali and drive off
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This sali is employed in glandular complainis With some effeci. It was formerly known in chemistry under the nameos ed Ammoniae, Dom iis being obtained by a process similar to that now used . Ιis modern adoption is oWing to Four-croy, and in this country to Dr. Beddoes, and it has also been employed by iis solution in Water, for the production ofiniense artificiat cold by Mr. Walher. It consisis, accoriang
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In the former Pharmacopoeia lime Was ranked among the articles of Materia Medica, and taken as prepared for iis coarser Uses in the ariS: for many purposes this might bosussicient, but for others it is osten important that it shouldbe much purer, and more certain, and the present directions arethere re introduced. T vo varieties of the carbonale also ars talaen Dom Whicti it may be prepared ; lime-stone and shelis ofoysters : the lalter of whicli usualty contains tess foreigii admixture : but even the former thus prepared will be much
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purer than that whicli is usually made frona chath. Carbona te of lime consisis, according to Kirwan, of . 45 carbonicacid and . 55 lime. From whatever combination it be obtain-ed, lime is always the fame subStance, POSSeSSing the Same characters, and producing the fame effecis, though it may disser in the proportion of heterogeneous matters With Whichit is miXed; the distinctions, there re, Which vere formel ly made belween iis medicat qualities as obtained froin differ ent Solarces Were superfluous, and Will not, in the present State os science, be lihely to be rene ed by the present introduction of more than one. It is necessary to the perfectionos the lime that the carbonic acid should be entiret y e Xpel- led, and pure and good lime is not eastly obtained as an article os trade; in the preparation of the ordinary fori, this expulsion is very imperfectly made, for it is sussicient for alleommon purposes is it be burni so as to stahe on the additionos Water; on the other hand, it may also be noti ced, that where lime-stone is employed, the heat may be pushed too far and be too long continued. The pure eartiis Will not
they may, Under these circumstances, vitrisy, and form a Coating ΟVer the surtace of the lumps, which will defend themisom the action of water, and thus preverat their stahing orsolution: lime, there re, may thus he over-burni. The
evolved, part of the water rises in steam, and pari combines
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Tahe of Challi, a potanti. Add a s mali quantity of Water to thechath, and grin i it into a sine poWder; thro illis poWder into a large vesset fuit of Water, thera stir it, und ui ter a Shori interVal, POUrthe Supernatant turbid solution into uno thervesset, and Set it by that the poWder may subside; lastly, having po ured a Way the vater, dry the poWder.
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Aqua aluminis composita, P. L. I 8I. Aqua aluminosa bateana, P. L. I 745.
Tahe of Alum, Sulphate of Zinc, of each half an
Boiling Water, tWo Pinis. Dissolve ut the fame time the alum and sulphate os ginc in the water, and then Strain the solution through Paper.