1098 WATERS, MINERAL 



necessary (for the purpose of repairs) the taking-out of the meter. As it is arranged 

 that any two of the meters are of sufficient capacity to deliver the quantity required, 

 it will be apparent that this can be done while the regular supply is going on. 



Messrs. Walker and Son's duplex water-meter, figs. 2097 and 2098, is somewhat 

 different from this. The water passes into an annular chamber A, in which is a rotator 

 arbor, on which are fixed two measuring screws c, with their blades at contrary angles, 

 and on the same arbor, between these screws, are two cones, which serve to guide the 

 water smoothly on to the screw-blades, and likewise to lift the rotator off its lower 

 pivot and keep it suspended in its bearings whilst in action, thereby preventing end-pres- 

 sure. The water, by means of a partition, is divided as it enters, and it passes over 

 the screws at opposite sides in two streams of equal force. In the central compartment 

 the water is again divided into two streams, the one descending and passing between 

 the blades of the lower screw, and the other ascending and passing between the blades 

 of the upper screw ; these two currents join, and the water passes off by the outlet. 



The first example given, in some respects resembles a Barker's Mill ; while in the 

 other the revolutions of the screws are made to measure the quantity of water passing 

 through the meter. 



WATERS, iraXNERAIi. Those waters which contain such a proportion of foreign 

 matter as render them totally unfit for ordinary purposes, and give them a sensible 

 flavour, and a specific action upon the animjil economy, are called mineral waters. 

 They are various in their composition, temperature, and in their effect upon the 

 system. In regard to temperature they are divided into warm, thermal, and cold. 

 They are generally so far impregnated with acid or saline bodies as to derive from 

 them their peculiarities, and are commonly divided into four classes. Acidulous or 

 carbonated waters are characterised by an acid taste, and by the disengagement of 

 gas. They contain five or six times their volume of carbonic acid gas ; their 

 salts are muriates and carbonates of lime and magnesia, carbonate or sulphate of 

 iron, &c. Saline waters contain, in general, salts of soda and lime, or of magnesia 

 and lime, with carbonic acid and oxide of iron. Chalybeate or ferruginous waters 

 have a decided styptic taste ; the iron is sometimes in the state of an oxide, held in 

 solution by carbonic acid, sometimes exists as a sulphate, and sometimes both as a 

 sulphate and carbonate. Sulphureous waters are easily recognised by their disagree- 

 able smell, and their property of tarnishing silver and copper. 



Dr. Gairdner, in his ' Natural History of Mineral and Thermal Springs,' has en- 

 deavoured to generalise the connection between the composition of mineral waters 

 and the rock-formations from which they flow: 1. 'The salts held in solution in 

 mineral waters have no connection with the acid, saline, or earthy matter which enter 

 into the composition of the rocks which they traverse in their passage to the surface 

 of the earth. 2. The mineral waters of the primitive formations are almost all 

 thermal, and generally possess a very high temperature. Their predominant im- 

 pregnation is sulphuretted hydrogen gas, free carbonic acid gas, carbonate of soda, 

 and, in general, salts with a base of soda, silica, few calcareous salts, except carbonate 

 of lime in some peculiar situations, and but a small quantity of iron. 3. The waters 

 of the palaeozoic and older secondary formations participate in those belonging to the 

 primitive rocks. They are generally of a lower temperature, though some of them 

 are still very hot ; free carbonic acid is much less common, and sulphuretted hydrogen 

 is almost entirely absent. Salts of soda still predominate, but carbonate is not so 

 common; sulphate of lime is found in the greater number of these waters; silica 

 exists in but two or three examples. 4. The waters of the newer secondary and 

 tertiary formations are as distinctly characterised as those of the primitive rocks, 

 placed at the other extremity of the series. They are all cold. Free carbonic acid is 

 almost entirely absent. Their predominant ingredients are the carbonate and sulphate 

 of lime, sulphate of magnesia, and oxide of iron. 5. The trachytic and basaltic 

 formations, and modern volcanic rocks, present in their mineral waters many of the 

 circumstances of temperature and composition which are found in the waters of granite 

 and other primitive rocks. Sulphuretted hydrogen, carbonic acid, carbonate of soda, 

 carbonate of lime, and silica reappear, and many contain the free sulphuric and 

 hydrochloric acids. The sulphate of lime, magnesian salts, and oxide of iron, are again 

 wanting. 6. It is often found that the mineral waters of a district have almost the 

 same composition, in which case they generally issue from the crystalline and 

 independent formations. In other cases they are subject to great varieties within a 

 comparatively limited space, so that waters of a totally different composition rise close 

 to each other when they emerge from sedimentary rocks. 



Sir Charles Lyell, in his Address at the meeting of the British Association at Bath, 

 stated that, 'Notwithstanding the general persistency in character of mineral waters 

 and hot springs ever since they were first known to us, we find on enquiry that some 

 few of them even in historical times have been subject to great.changes. These have 



