W A T

WAT

( 476 )

iron by expofure to air, fo that the track ofthefe lprings on the foil is marked by a line ofreddiih yellow ochre.

19. Copper is only found as a fulphat, and inthe neighbourhood of copper pyrites, from thedecompoiition of which it originates. It isftrongly marked by the cupreous tafte.

20. Mdnganefe difiblved in the muriatic acidhas been found.

21. Befides thefe ingredients there is oftenfound diffolved in water a fmall quantity of ablack matter, not cryftaliizable, foluble in alco-hol, deftrudtible by fire, which gives a blacktinge to fuiphuric acid, and is obvioufly carbo-naceous. its quantity is always too fmall forminute examination, but it is ufually confideredas a kind of bitumen. This appears differentfrom the foluble part of decayed vegetablematter which water fometimes meets with andholds in folution ; and is equally dittindt fromthe mucilage which is generated in water whennearly ftagnant, from the growth of confervasand other aquatic vegetables.

Some arrangement of mineral waters hasbeen attempted by different writers on the fub-jeft. This however is of little importanceexcept as relates to their medicinal powers, foreven among thofe kinds that relemble eachother the moft, fuch as the carbonated, tirechalybeate, the fulphurous, &c. the individualwaters often differ fo much in chemical ana-lyfis as to require to be admitted as feparategenera in any methodical arrangement. Thediftinction of warm and cold fhould howeverbe noticed, the former being uniformly abovethe average temperature of the air into whichthey rife. Of thefe there are many in theneighbourhood of adtual volcanoes, or in coun-tries obvioufly volcanic, which have the tempe-rature of 212° when they burft into day, andin all probability are much hotter before. Suchboiling lprings are found in Iceland, in Italy , inSouth America , and in great abundance inKamlcitr.-ka. In inis country the Bath water isthe hoiteft natural fpring that we poflefs, whichrifes to 11C 0 . The cooleft of our therm. 1waters is the Matlock, which is fleadily at 6o°in the co'deit winters.

We proceed to the befl mode of examininga mineral water, in which lome differencesexift among the beft'chemilts.

1 he physical properties of the water fhouldbe firfc noticed.

Thefe are the degree of clearnefs or limpi-dity—fparkiing or bubbling when poured intoa glafs—the tafte—fmell—fpecific gravity—■

and temperature. It is ufeful alfo to mark theftrata of foil from which it fprings, the copioul-nefs of the fpring, and whether this is airi diedby a dry or wet feafon, whether any vegetables,filhes, or animalcule are found in it, and whetherit incrufts the fubftances over which it flows, ordepofits any fediment.

The next ftep is the application of tejh ofdifferent kinds, which is of the utmoft import-ance, as by thefe the nature and number of allthe foreign ingredients (with one or two excep-tions) may be difeovered, and even feme opinionmay be formed of their relative quantity, andthefe fa£ts are the guide by which the futureanalyfis is conducted. Several precautions how-ever are required in the application of tefts toavoid deceitful appearances, and the tefts them-felves fhould be prepared with great care, whichmay be the more readily done as very minutequantities judicioufly applied will anfwer everypurpofe. Moft of the tefts indicate the fub-ftances for the detection of which they are uled,by producing a fenfible turbidnefs which gradu-ally collects into a precipitate. There is how-ever with all a limit to this power of precipi-tation, for when two naturally incompatiblefalts are mixed together in very dilute folution,the decompoiition is totally prevented by thegreat bulk of water compared to the falinematters. Thus very fmall quantities- of fulphatof lime and carbonat of loda will coexilt in thefame water, and thefe will not be mutually de-compofed till the bulk of liquid is reduced byevaporation. In like manner minute quantitiesof fulphat of magnefia and muriated lime, orof muriated lime and fulphat of foda,. may becontained in the fame water.

Another limit to the power of tefts is wherethe intended decompofition does indeed takeplace, but where the quantity of liquid is folarge that the refuhing compound, inftead ofbeing precipitated, remains fufpended in thewater.

The principal tefts are the following :

Litmus. The infufion or tindture of litmusfold in the (hops is a thick liquor of a very darkpurple, containing a great body of co.our. Thepurple of litmus is changed to red by everyacid, fo that this is the teft utually applied todilcover any excefs of acid in mineral waters.It may be uled either by dipping into the watera paper ftained with litmus, or by adding a dropof the tinct ure to the water to be examined,and comparing its hue with that of an equ.dquantity of the tindture in diftilled water. Inthis latter way the change is produced more