WATER. 



■mean temperature, is ftated to abforb from f ds to ^ths of 

 its bulk of this gas, and by long agitation more than its 

 bulk. At a temperature of 80° or 90°, however, this fluid 

 can with difficulty be made to diflblve any of it. Sul- 

 phuretted waters, therefore, on expofure to heat, or even 

 to the open air without heat, foon lofe their charadleriflic 

 properties, and become turbid, the hydrogen being difli- 

 pated, and the fulphur depofited. The fource of this gas, 

 in general, is not obfcure, it being formed in great abun- 

 dance during the decompoStion of pyrites, and other mine- 

 rals containing fulphur. Phofphuretted hydrogen is faid 

 to be occafionally extricated from marfhes and ftagnant 

 pools, but it is not known to conllitute an ingredient in 

 mineral waters. 



5. The Alkalits and their Salts. — The fixed alkalies feldom, 

 if ever, occur in natural waters in a free flate. Even the 

 number of their falts is fo limited, that Dr. Saunders 

 thinks it neceffary to enumerate only two, namely, the ful- 

 phate and muriate of foda. The firft of them is a very 

 common ingredient in mineral waters, but rarely occurs 

 alone in any quantity, fo that it can hardly be faid ever to 

 give a peculiar charafter to a water. Muriate of foda is 

 fo extenfively and abundantly diffufed through nature, 

 that we rarely meet with a natural water which does not 

 contain more or lefs of it. Sea-water, and many natural 

 waters or brines, owe their peculiar charadlers to this fait, 

 which has been known from the earlieft times, and fecms to 

 be almoft a neceffary ingredient in our food. The muriate 

 of foda, however, never occurs alone in natural waters, but 

 is commonly accompanied by fome of the earthy falts, 

 efpecially the fiilphate of lime. Chemilts have been puz- 

 zled to account for the origin of the vaft quantity of this 

 fait which is met with in the fea and elfewhere ; but a 

 little refleftion will (hew, that the exiftence of this fub- 

 ftance is not more difficult to be accounted for than that 

 of any other ingredient of our globe. From its property 

 of being foluble in water, it is, perhaps, more generally dif- 

 fufed than any other principle ; but it is doubtful if it 

 aAually exids in greater abundance than filex, and many 

 other folid fubftances, and which, in a geological point of 

 view, differ from it only in the mechanical circumftance of 

 their infolubility in water. The carbonate of foda is occa- 

 fionally met with in waters. Its diftribution, however, is 

 very partial, being ufually in very minute quantities, or in 

 very large ones. When in fmall quantity, it is generally 

 fupcrfaturated with carbonic acid. The mod remarkable 

 inftance of an excefs of this fait is in " the natron lakes 

 of Upper Egypt. It is here often mixed with common 

 fait, and they both are largely didolved in the water, and 

 form a cruft of feveral feet in thicknefs at the edge of the 

 lake, owing to the copious evaporation of their water of 

 folution etfefted by a tropical fun." Potafli, or its falts, 

 very feldom occur in mineral waters. Carbonate of am- 

 monia is occafionally found in fmall quantities in fome waters, 

 arifing probably, as Dr. Saunders conjeftures, from decom- 

 pofed animal or vegetable fubftances. 



6. The Earths and their Salts. — The earth moft fre- 

 quently occurring in natural waters is lime, and fo gene- 

 rally is this the cafe, that very few inftances are known in 

 which this earth is not met with in fome ftate or other. 

 The neutral carbonate of lime, or chalk, is one of the moll 

 infoluble fubftances known ; but the fupercarbonate of 

 lime is very foluble, and is a frequent ingredient in many 

 fprings. " It is one fource of hardnefs in waters," fays 

 Dr. Saunders, " but is eafily got rid of by boiling, which 

 drives off the excefs of carbonic acid, and thus caufes the 

 chalk to be precipitated ; hence the earthy cruft. or furr on 



kettles m which hard water has been boiled for a number of 

 times. Some natural waters contain an unufual quantity of 

 this calcareous earth, which is rapidly depofited as foon at 

 they become expofed to the air, and thereby give an earthy 

 hning to every tube through which they flow, and encruft 

 with the fame material every fubftance that accident or 

 defign may put in their way. Of this kind are the various 

 petrifying fprings that form part of the natural curiofities 

 of feveral mountainous diftrifts, and have been applied to 

 life in a very ingenious manner at the baths of St. Phihp, 

 in Tufcany, and ftill more extenfively at Gualecavelica, in 

 Peru."—" The fulphate of lime (the gypfum or felenite of 

 the older writers) is one of the commoneft of all the earthy 

 falts that are found in natural waters, and generally ac- 

 companies every faline fubftance, except where there is an 

 excefs of alkali. It is almoft invariably found in con- 

 junftion with the carbonate of lime ; and hence the calca- 

 reous depofitioi.s, petrifaftions, and the like, frequently con- 

 tain a fmall admixture of felenite." This fait imparts very 

 little tafte to water, but gives it " that rough and harfh 

 feel to the fingers and tongue, which charafterize the 

 infipid hard w.iters." The muriate of lime commonly ac- 

 companies the other falts of hme, but efpecially the muriate 

 of foda. When in excefs in any water, it imparts to it a 

 bitter and difagreeable tafte, and aftive medicinal properties. 

 The great bitternefs of " the waters of the Dead fea is 

 owing to the muriates of lime and magnefia, and not to 

 bitumen, as was erroneoufiy fuppofed." The carbonate of 

 magnefia is infoluble in water ; the fupercarbonate of 

 magnefia, when it occurs in waters, is always accompanied 

 by the fupercarbonate of lime, both the earths being held 

 in folution by an excefs of carbonic acid. The fuper- 

 carbonate of magnefia, however, is more foluble than the 

 fupercarbonate of lime, and is not, therefore, fo -eafily 

 feparated by boiling. The fulphate of magnefia, or Epfom 

 fait, as it was formerly denominated, is the moft important 

 of the falts of this earth. It almoft always accompanies the 

 fulphate of foda ; and to thefe two falts moft of the natural 

 purging waters owe their cathartic properties. It is like- 

 wife frequently combined with the fulphate of lime, and 

 alfo with iron. The fulphate of magnefia imparts to the 

 waters containing it in any confiderable quantity a ftrongly 

 bitter and faline tafte. It was firft difcovered in a fpring 

 at Epfom, whence its name ; but is ufually prepared at 

 prefent from the refufe fait of fea-water, after the common 

 fait has been feparated. The muriate of magnefia, as before- 

 mentioned, commonly accompanies the muriates of foda and 

 lime ; hence it is found in various briue-fprings, and forms 

 a confiderable part of the faline contents of fea-water, to 

 which fluids, efpecially when concentrated by evaporation, 

 it imparts a ftrong bitter tafte. Salts of alumina are not 

 of very frequent occurrence in waters. The moft common 

 is the fuperfulphate of alumina, or common alum, which is 

 ufually aftbciated with the fulphate of iron. The fource 

 of this fait is for the moft part alum-flate, the fulphur 

 contained in which becomes acidified on expofure to 

 the air, and forms fulphuric acid, which, uniting with the 

 alumina, produces the fait in queftion. The prefence of 

 the fulphate of iron is eafily accounted for upon fimilar 

 principles, fince more or lefs of iron ppiies almoft in- 

 variably accompanies alum-flate. Silex, in a ftate of mi- 

 nute divifion, is fometimes found fufpeiided in fmall 

 quantity in running waters, but is foon depofited on their 

 remaining at reft. This earth, however, occafionally occurs 

 in a ftate of folution in hot and tepid fprings, efpecially in 

 the neighbourhood of volcanoes. The menftruum apjjears 

 to be ufually a littje free or carbonated alkali, the folvent 

 B 2 powers 



