WAT

WAT

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fpeedily, and the power of the tefl is fo great,that the a£l of b owing through litmus water,diluted fo as to be barely coloured, will veryfenfibly alter the hue by means of the carbonicacid of the breath which unites with it. Itffiould be remembered that paper or muflinitained with litmus fpontaneouily reddens byexpofure to ail, alfo that the colour is nearlydeltroycd by long expofure to light, fo thatwhen ufed as a ted they fhould be recentlyftained. Litmus is alfo reddened by fulphu-retted hydrogen.

As the acid of mineral waters is generally thecarbonic, and as this acid, when uncombinedwith any bafe or in excefs (in which cafe aloneit atls on litmus as an acid] is expelled by boil-ing for a few minutes, the trial of litmus beforeand after ebullition will determine whether theacid of the water is fixed or volatile.

Litmus already leddenedbyan acid will haveits purple reltored by an alkali, and thus it mayalfo be ufed as a ted for alkalies, but it is muchlefs active in this refpe£t than other dirett alka-line teds.

2. Red Cabbage has been found by Mr. Watt 3to furniih as delicate a ted for acids as litmus, andto be dill more fenuble to alkalies. The naturalcolour of an infufion of this plant is blue, whichis changed to red by acids, and to green by al-kalies in very minute quantities. 'I he colouris extracted limply by infufing the freth leavesof the plant in warm water of about I .o c for afew hours. The difadvantage of this liquorhowever is that it is peculiarly liable to changeby putrefa&ion , when its properties as a tedare lod. To preferve the cabbage for a lengthof time Mr. Watt advifes to mince the leaves,ipread them on paper, and dry them with agentle heat, and then put them in ciofely corkedbottles. When to be ufed, diged fome of theleaves in a very dilute vitriolic acid which willgive a red liquor; bring this to exact neutrali-zation by chalk, fo that the colour is a pureblue inclining neither to green nor purple, andthen pour off the clear liquor and employ it.By adding a little alcohol it will keep good forfome days.

3. Brazil Wood. When chips of this woodare infufed in warm water they yield a redliquor which readily turns blue by alkalies,either caudic or carbonated- It is alfo bluedby the carbonated earths held in folution bycarbonic acid, fo that it is not an unequivocalfceit of alkalies till the earthy carbonats have

been precipitated by boiling. Acids change teyellow the natural red of Brazil wood, andredore the red when changed by alkalies.

4. Violets. The delicate blue of the com-mon feented violet is readily changed to greenby a kalies, and this affords a delicate ted forthefe fubdances. Syrup of violets is commonlyufed, as it is generally at hand, being ufed inmedicine, but a tinflure of the flower willanfwer as well.

5. Turmeric. This is a very delicate tedfor alkalies, and on the whole is perhapsthe bed. The natural colour of turmericeither in watery or lpirituous infufion is yellow,which is changed' to a brick or orange red byalkalies, caudic or carbonated, but not by car-bonated alkaline earths, on which account it ispreferable to Brazil wood. The pure earths, fuchas lime or barytic water, produce the fame change,but thefe are never found in mineral waters.

6. Rhubarb. Infufion or tindfure of rhubarbundergoes a fimilar change with turmeric, andis equally delicate.

7. Sulphuric Acid . A drop or two of con-centrated fulphuric acid added to water that con-tains carbonic acid, free or in combination, caufesthe latter to efcape with a pretty brilk effervef-cejice, whereby the prefence of this gafleousacid may be detefted.

8. Nitric and Oxymurialic Acid. A peculiarufe attends the employment of thefe acids inthe fulphuretted waters, as the fulphurettedhydrogen is decompofed by them ; its hydrogenis ablorbed, and the fulphur feparated in itsnatural form. The theory of this operation hasbeen fully explained under the article Siilphuret.

9. Oxalic acid and Oxalat of Ammonia. Ox-alic acid is the mofc delicate tell for lime thatwe are acquainted with, as it decompofes all thefoluble calcareous {alts, and precipitates withthe lime as an infoluble oxalat. This precipi-tate when collected and dried, and ltronglyheated, blackens and melts, and the acid burningoff, the lime is left white and carbonated. Ox-alat of lime, though nearly infoluble in water,diffolves without difficulty in a moderate quan-tity of its own or any.other acid, and hence inanalyfis oxalat of ammonia is often preferredas no excefs of this fait can redifiolve the preci-pitated oxalat ol lime. On the other hand theammonia fhould not exceed, otherwife it mightgive a falfe indication.

10. Gallic Reid and Tincture of Galls. Thiswell known tefl of iron is peculiarly ufeful inthe examination of mineral waters, as this i*

Vliil. Tjant. V&l. Uxiiii.