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2,500 feet in elevation, contains soda enough to supply the Karlsbad waters alone for more than 30,000 years.” {Ibid. p. 338).
Division and Properties. —Mineral waters may be classified accord-ing to their temperature, their chemical composition, or their medicinalproperties. But hitherto no satisfactory classification has been effectedby any of these methods, nor perhaps can it be formed. The most con-venient arrangement is that founded on chemical composition, and whichconsists in grouping mineral waters in four classes.
Class 1. Chalybeate, ferruginous, or martial waters.{Aquae miner ales ferruginosae; aquae martiales ).—Oxide of iron is a con-stituent of most mineral waters, and when the quantity is considerable,the term chahjbeate is applied to them. Chalybeate waters have aninky, styptic taste, and the property of becoming purplish black on theaddition of tannic or gallic acids, or of substances which contain these,as the infusion of galls or of tea. If the iron be in the state of sesqui-oxide, the ferrocyanide of potassium causes a blue, and sulphocyanideof potassium a red colour.
Most chalybeate waters contain the carbonate of the protoxide of iron;and are termed carbonated-chalybeates. Such waters, when exposed tothe air, evolve carbonic acid, attract oxygen, and deposit the sesquioxideof iron. By boiling also, the whole of the iron may be precipitated assesquioxide. When the protocarbonate of iron is associated with aconsiderable quantity of free carbonic acid, the waters are termedacididous-carbonated-chalybeates, or simply acidulous-chalybeates ; as thecelebrated waters of Spa in Belgium . When a carbonated-chalybeatecontains alkaline and earthy salts, but not much free carbonic acid, it istermed a saline-carbonated-chalybeate; as the waters of Tunbridge Wells ,Oddy’s saline chalybeate at Ilarrowgate, and the Islington Spa nearLondon .
In some cases the oxide of iron is in combination with sulphuric acid :these waters might be termed, in contradistinction to the above, sul-phated-chalybeates. Exposure to the air, or boiling, does not precipitateall the iron, and in this they are distinguished from the carbonated-chalybeates. The sulphated-chalybeates usually contain sulphate ofalumina, and, in that case, are termed aluminous-chalybeates : of these,the Sand Rock Spring, Isle of Wight , the strong Moffatt Chalybeate,and Vicar ’s Bridge Chalybeate, are examples: the last-mentioned isprobably the strongest chalybeate in existence.
The effects of chalybeate waters are analogous to those of otherferruginous compounds which I shall have occasion to notice in asubsequent part of this work, and to 'which, therefore, I must refer forfurther information. I may, however, mention here that these waters aretonic, stimulant, and astringent, and produce blackening of the stools.The acidulous-carbonated-chalybeates sit more easily on the stomachthan other ferruginous agents, in consequence of the excess of carbonicacid present. The aluminous-chalybeates are very apt to occasion car-dialgia, especially if taken in the undiluted state.
The use of this class of waters is indicated in cases of debility, espe-cially when accompanied with that state of system denominated anaemia.It is contra-indicated in plethoric, inflammatory, febrile, and haemorrhagicconditions.
Class 2. Sulphureous or hepatic waters. (Aquae minerales
i.