905 



BARIUM. 



BARK. 



fioa 



it is still more insoluble in water containing any salt in solution. It is 

 poisonous, and suffers no change by exposure to the air. When 

 heated to whiteness with charcoal it is decomposed, and on the addition 

 of water a solution of baryta is obtained. It consists, according to Dr. 

 Thomson, of 



1 equivalent of carbonic acid . 

 1 do. baryta 



2-2-0 

 76-6 



98-6 



It is used for the purpose of dissolving in various acids to procure 

 barytic salts, and, when heated with charcoal, also for preparing baryta, 

 especially when it is wanted merely in solution in water. Bicarbonate 

 and sesquicarbonate of br.ryta may be formed, but they are unimportant 

 compounds. 



yi Irate of Han/ta (BaO, N0 5 ) is readily procured by adding nitric acid 

 either to baryta, its carbonate, or to the solution of protosulphide of 

 barium. The solution is colourless, and by evaporation yields crystals, 

 the form of which is the regular octahedron. 



This salt requires 12 times its weight of water at 60 for solution, 

 and between 3 and 4 times its weight at 212. It is not altered by 

 exposure to the air, but when strongly heated it is, as already noticed, 

 decomposed, and baryta remains in a pure state. This salt consists of 



1 equivalent of acid ..... 54'0 

 1 do. baryta 76'ti 



130-0 



The crystals contain no water. 



XtiljJiate itf Barijhi (BaO, S0 3 ) ; Heavy Spar. This compound occurs 

 largely in many parts of Great Britain, especially in the lead-mines of 

 the north of England. It occurs both amorphous and crystallised. In 

 the former state it is sometimes colourless and transparent, but fre- 

 quently opaque. The crystals are often very large, and the primary 

 form, subject to many varieties, is a rhombic prism. It is extremely 

 heavy, its specific gravity being about 47. It is unalterable in the air, 

 insipid, and insoluble in water ; indeed, strong sulphuric acid is the 

 only fluid which dissolves it in any notable quantity, and from this it 

 is precipitated by water. It is composed of 



1 equivalent of sulphuric acid 

 1 do. baryta 



40-0 

 76-6' 



116-0 



Sulphate of baryta may also be prepared artificially by adding either 

 dilute sulphuric acid or any soluble sulphate to a solution containing 

 baryta or any of its salts. The sulphate of baryta precipitates as a 

 heavy white powder, insoluble in water, acids, and alkalies. 



Heat produces no decomposition in sulphate of baryta ; but, as 

 already noticed, when heated with charcoal it is converted into sul- 

 phide of barium. When boiled also in a solution of carbonate of 

 potash, a portion of it is converted into carbonate of baryta ; but the 

 decomposition takes place only to a limited extent. 



On account of the extreme insolubility of sulphate of baryta, its 

 constituents are delicate tests of each other's presence, and both sul- 

 phuric acid and baryta are almost invariably converted into this salt 

 when their weight has to be estimated in quantitative analysis. 



When sulphate of baryta is moderately heated with carbonaceous 

 matter, a substance is produced called BetogiMM phoiphia-ns, which 

 possesses the property of exhibiting luminosity in the dark for some 

 time after it has been exposed to the direct rays of the sun. 



BARIUM, SALTS OF. [BARIUM.] 



BA'RIUM, CHLORIDE OF Medical Properties o/. This compound 

 never occurs native, but is always obtained either by the decomposition 

 of the native carbonate of barytes, or witherite, as directed by the 

 London Pharmacopoeia, or of the sulphate, or heavy-spar, as directed 

 by the Edinburgh College. This List seems the preferable mode, not 

 only from the abundant occurrence of heavy-spar, but because the salt 

 so procured is generally purer (Christison) ; and as it is more employed 

 as a chemical test than in medicine at the present day, purity is an 

 essential condition for its utility. It crystallises in white, transparent, 

 shining, right rhombic prisms, sometimes in double eight-sided pyra- 

 mids, or, by rapid evaporation, in thin plates (Geiger). It is perma- 

 nent at the ordinary temperature of the air, but efflorescent in a very 

 dry atmosphere. Its specific gravity is 2-825. It is of easy solubility 

 in water : 100 parts dissolve 43'5 at 60 Fahr. ; at 212, 78 parts. Pure 

 alcohol does not dissolve any of it ; rectified spirit, a minute quantity. 

 The only officinal preparation is the watery solution, Liquor Barii 

 C'hloridi. 



Chloride of barium possesses acrid-narcotic properties, its taste being 

 irritating and burning. It resembles medicinally chloride of calcium, 

 , but is more potent ; in poisonous doses its action is similar to arsenic, 

 with this difference, that it requires a larger dose to destroy life, and 

 while its local action is less marked, producing less disintegration of 

 the stomach, it is more rapidly absorbed and produces death more 

 speedily. It is rarely employed as a means of self-destruction, or of 

 intentional injury to others. Fortunately an efficient antidote exists 

 in agents readily procured, and invariably efficacious if speedily 

 administered. Any alkaline sulphate, such as Epsom or Glauber 



salts, or sulphuric acid greatly diluted, will instantly form an insoluble 

 and harmless sulphate of barytes. Medicinally this compound is 

 employed in very minute doses in various forms of scrofula. It pos- 

 sesses slight tonic powers, improves the appetite, and promotes 

 absorption, reducing the glandular enlargements. It once enjoyed, 

 chiefly from the testimony of Hufeland, a high celebrity. But like 

 many other muriates once confided in for the removal of scrofula, it 

 has almost fallen into disuse, particularly since iodine has become 

 known. Some practitioners, thinking that two agents which are 

 thought singly to be of use, must do good when combined, have formed 

 an iodide of barium. This salt has a disagreeable nauseating taste. 

 It is given in the dose of the eighth of a grain, in some aromatic water, 

 three times a day. An ointment is also formed of it. 



Pure air, exercise, regular, and above all early hours, appropriate 

 diet, and other points of regimen, such as warm clothing, will do more 

 to eradicate scrofula than any medicines. 



(Lugol, On Scrofula, translated by Ranking, 1844.) 



BARK. There are several kinds of bark which enter largely into 

 commerce, and are used for processes in the arts, or for medicines. 

 The principal kinds in the first of these classes are the barks of the 

 oak, the cork, the mimosa, and the quercitron. Among the descrip- 

 tions of bark used for medicines we shall notice only that known under 

 the name of Jesuits' or Peruvian Bark : the others are not of much 

 commercial importance. Some other kinds of bark, as Cinnamon and 

 Cassia, will be noticed in other parts of this work. 



Oak Baric. (German, Eichenrinde Lake; Dutch, Run, Sunne ; 

 Danish, Bart, Garverbart ; Swedish, Bark, Ekhai-k ; French, Tan 

 Brut, Scarce dc Chine; Italian, Scoria di Quercia Corteccia della 

 Quei-cia,; Spanish, Corteza de Encina ; Portuguese, Casca do Can-allio ; 

 Russian, Uitbuwui Kvra ; Polish, Dab Garbarski; Latin, Quercuii 

 Cortex.) For a long tune, oak-bark was the only substance used in 

 England for the process of tanning ; and it was thus employed for 

 ages, without the tanners knowing what were the properties of the 

 substance which produced the chemical change whereby hides are 

 converted into leather. The increasing demand for oak-bark beyond 

 the means of supply so raised its marketable value, that an inves- 

 tigation became necessary, in order to ascertain whether, when the 

 nature of those properties was discovered, some cheaper substances 

 might be found to answer as substitutes. Other substances besides 

 oak-bark had before that time been used for tanning in certain foreign 

 countries; such as heath, gall-nuts, birch-tree bark, myrtle-leaves, 

 leaves of wild laurel, and willow-bark. In 1765 oak saw-dust was 

 applied with some success in England to the purpose of tanning ; and 

 this plan has been since pursued in Germany. 



The result of investigations showed that the tanning power of oak- 

 bark resided hi a peculiar astringent substance, to which, from the 

 use to which it is applied, the name of tannin has been given. In 

 more recent times, Sir Humphry Davy determined, by a series of 

 experiments, the relative value to the tanner of different substances 

 in which tannin is found ; and he has shown that 8 Ibs. of oak-bark 

 are, in this respect, equal to 2| Ibs. of galls, to 3 Ibs. of sumach, to 

 74 Ibs. of bark of the Leicester willow, to 11 Ibs. of bark of the 

 Spanish chestnut, to 18 Ibs. of elm-bark, and to 21 Ibs. of common 

 willow-bark. 



To prepare oak-bark for use, it is ground to a coarse powder between 

 cast-iron cylinders, or in bark-mills which implement makers have 

 lately invented. In the ground state it is put into the tan-pit, in 

 alternate layers, with the skins to be prepared. A better method 

 sometimes employed is to make an infusion of the bark in water, 

 which dissolves and holds the tannin. The action of this substance 

 upon skins may be explained in a few words. Before the skin ia sub- 

 jected to the tanning process, the hair, epidermis, and any fleshy or 

 fatty parts adhering to them, must be removed; the remainder con- 

 sists wholly of gelatine, a substance capable of being dissolved in 

 water, and which then forms the substance well known as glue. 

 Tannin, as we have seen, is likewise readily soluble in water ; but the 

 two substances, when brought together, form the insoluble and im- 

 putrescent compound called leather. See further on this subject 

 under TANNING. 



It has been found that the proportion of tannin which oak-bark 

 contains varies materially according to the season in which it is cut. 

 If taken in the spring, it has four and a half times the quantity, in a 

 given weight, compared with what it would have if cut in winter. 

 Sir Humphry Davy likewise discovered that the proportion is in- 

 fluenced by the age of the tree, tannin being more abundant in the 

 bark of young than of old trees. 



There are no means of knowing what quantity of oak -bark is used 

 annually by the tanners of this country. Of that which is imported, 

 about half comes from Holland and Belgium. 



Cork Bark. This substance is described in a separate article. [OoiiK 



AND COKK-CUTTING.] 



Mimosa, or Wattle Bark. This bark is collected from two species of 

 the mimosa, which are plentifully found in New South Wales, Van 

 Diemen's Land, and New Zealand, where, at least in the British 

 settlements, it is used for the manufacture of leather. This bark 

 contains about 150 Ibs. of pure tannin in every ton weight, which is 

 only about three-fifths of the proportion yielded by the best white 

 oak bark. It is also said that it gives a reddish colour to the leather, 



