WATER. 



powers of which are doubtlefs much increafed by heat, or 

 by fome unknown caiife. 



7. Metals and their Salts The metal moft ufually met 



with in natural waters is iron ; never, however, in its me- 

 tallic ftate, but in a ftate of oxyd combined with an acid. 

 The carbonate of iron is a frequent ingredient of natural 

 waters, the bafe of which is the black or protoxyd of the 

 metal, for the red oxyd does not feem capable of combining 

 with carbonic acid, or at leall of forming with it a foluble 

 compound. This is, doubtlefs, a wife provifion of nature ; 

 for, as Dr. Saunders julUy obferves, if the contrary were 

 the cafe, almoll every natural water would be a chalybeate. 

 The carbonate of iron, like all the other falts of this metal, 

 imparts to waters containing it a peculiar inky tafte, 

 " which," fays Dr. Saunders, " is very perceptible, even 

 when the proportion of iron is fo fmall as hardly to be 

 ettimable by any chemical procefs." Waters containing 

 the carbonate of iron depofit this metal readily on expofure 

 to the air, partly from the efcape of the carbonic acid, and 

 partly from the further oxydation of the metal. The ful- 

 phate of iron or green vitriol is met with occafionally in 

 waters in confidernble quantity. This fait, as before ob- 

 ferved, generally occurs in union with the fulphate of alu- 

 mina, or alum, and is the natural produftion of the decom- 

 pofuionof iron pyrites. Waters containing this fait in any 

 quantity, poffefs the properties of chalybeates in a high 

 degree, and are peculiarly ftyptic. The muriate of iron is 

 occafionally met with in natural waters ; but its exiftence 

 in any confiderable quantity is a rare occurrence. Copper, 

 or rather its falts, and efpecially the fulphate of copper, is 

 occafionally met with in natural waters. This generally, 

 however, occurs in the neighbourhood of copper-mines ; 

 and the fulphate of copper, as Dr. Saunders obferves, is 

 probably formed, like the fulphate of iron, by the decom- 

 pofition of copper pyrites. Waters containing this metal 

 are highly poifonous, and are never ufed internally. Man- 

 ganefe is occafionally found in fmall quantity in natural 

 waters. It appears, in general, to be ailociated with iron ; 

 but the ftate in which it exifts is not accurately known. 

 As far as prefent obfervation goes, it imparts no fenfible 

 or other properties to the waters containing it. Lead, per- 

 haps, never naturally occurs in waters ; but fome waters 

 have the property of difTolving, or holding in fufpenfion, a 

 minute portion of this pernicious metal, when expofed to it 

 in the metallic ftate. Pure foft waters are faid to poffefs 

 this property in the moft ftriking degree. 



8. Mineral Acids. — Both the muriatic and fulphuric acids 

 are occafionally met with in mineral waters in a free ftate. 

 Such fprings ufually occur in volcanic countries. 



9. Bitumen. — Bitumen is faid by many of the older 

 writers to be a frequent ingredient in mineral waters. This 

 ftatement, however, has been generally found erroneous by 

 modern chemifts, who have in moft cafes demonftrated the 

 fuppofed bituminous principles of their predeceffbrs to be 

 fubftances of a very different nature. There are fome 

 fprings, however, which yield a real bitumen ; but this, 

 from its infolubility in water, is never diflblved in that fluid, 

 except in a few rare inilances, through the medium of an 

 alkah. 



Such is a ftiort account of the principal mineral fub- 

 ftances which are met v^ith in natural waters when they 

 iftue from the earth. " When," fays Dr. Saunders, " they 

 flow within a channel over the furface of the ground, they 

 often become much changed in their chemical compofition, 

 lofing fome of their contents by evaporation, others by (low 

 depofition, or by being decompofed through the influence 

 of light and air. At the fame time they often acquire new 

 6 



contents, which are furnilhed by the foil over which they 

 flow. Thus the ftreams which pafs over a country covered 

 with vegetable matter, or which water large towns, will 

 contain a fenfible quantity of mixed alluvial contents, or a 

 heterogeneous compound of animal and vegetable extraft of 

 mucilage. 



Different authors have chofen different principles of 

 arrangement in treating of natural waters. An arrange- 

 ment purely chemical, or purely medicinal, cannot be 

 effefted in the prefent ftate of our knowledge ; we (hall 

 not therefore attempt either, but ftiall confider them under 

 the following heads : 



1. Potable waters. 



2. Saline waters. 



3. Chalybeate waters, fimple and compound. 



4. Acidulous waters, fimple and compound. 



5. Sulphureous waters, fimple and compound. 



6. Thermal waters, fimple and compound. 



This arrangement of natural waters, according to their 

 fenfible properties, coincides likewife, as well perhaps as 

 the prefent ftate of the fubjeft will admit, with their chemi- 

 cal and medicinal prooerties. It may, however, be objedled 

 to the diviPionsfinple and compound, that neither of them is 

 accurately correct, and this muft be admitted in a ftriAly 

 chemical point of view ; but taken in the enlarged and ge- 

 neral fenfe here underftood, there feems to be no ferious ob- 

 jeftion to this mode of divifion. 



1. Potable IVaters. — Under this divifion we wifh to in- 

 clude every variety of this fluid ordinarily ufed by mankind 

 and other animals for fatisfying their thirft. Thefe may be 

 comprehended under the heads of, a, pure or diftilled water ; 

 t, atmofpheric water ; c, fpring-water ; d, running water ; 

 and e, ftagnant water. 



a. The chemical properties of pure water have been al- 

 ready defcribed at the head of this article. As before ob- 

 ferved, it never occurs in nature, and was therefore pro- 

 bably never intended as an article of drink for mankind ; cer- 

 tainly, atleaft, not as one abfolutely neceflary for their ex- 

 iftence, or even healthy condition. 



L. Under atmofpheric waters are included rain-water, fnow- 

 water, dew, &c. 



Rain-water, colledled at a diftance from large towns, or 

 any other objcdl capable of impregnating the atmofphere 

 with noxious materials, approaches more nearly to a ftate of 

 purity than perhaps anv other natural water. Even coUedl- 

 ed under thefe circumftances, howevtr, it invariably yields 

 traces of the muriatic acid, and, according to MargraafF, 

 of the nitric alfo. Rain-water of courfe differs according 

 to the ftate of the atmofphere through which it paffes. 

 " The heterogeneous atmofphere of a fmoky town," fays 

 Dr. Saunders, " will communicate fome impregnation to rain 

 as it pafies through ; and this, though it may not be at once 

 perceptible on chtmical examination, will yet render it liable 

 to fpontaneous change ; and hence rain-water, if long kept, 

 efpecially in hot climates, acquires a ftrong in:ell, becomes 

 full of animalcula;, and in fome degree putrid." Rain-water 

 in general, in warm climates, is much more impure and lia- 

 ble to becom.e offei.five than in cold and temperate ones. 

 Rain alfo that falls in the fpring and lummer, or after a 

 long-continued drought, or very hot wea.her, is faid to be 

 more impure than that which falls at other feafons of the 

 year, or after a long-contii'ued nioiil fcafon ; circumftances, 

 doubtlefs, owing to the exiftence of a greater proportion of 

 animal and vegetable principles in the atmofphere in fuch 

 climates and feafons. Thefe foreign fubftances have fomc- 

 times been fo abundant and peculiar iu their appearance, as 



to 



