8 14 THE POPULAR SCIENCE MONTHLY. 



the gypsiferous beds and dolomites of the Trias. At Birmenstorf the 

 natural leaching of the gypsum rocks is imitated artificially ; and 

 either salt is dissolved according as it predominates in the particular 

 stratum on which the process is performed ; so that two kinds of 

 medicinal waters are prepared. The purgative springs of Sedlitz, 

 Seidschiitz, and Piillna in Bohemia, derive their sulphate of magnesia 

 from the Tertiary marl which they have traversed ; and, this fact once 

 recognized, similar waters have been produced for half a century by 

 washing the rock — an experiment which was the starting-point of the 

 artificial mineral-water industry. The origin of most of the sulphuret- 

 ed waters, or, to speak more exactly, of their sulphuret of calcium, is 

 explained by the facility with which the sulphates can yield their 

 oxygen to organic matters ; a thing which occurs notably when car- 

 bonaceous matters, lignite, stone coal, or bitumen, are found associated 

 with gypsum. 



The origin of gaseous or acid springs, which constitute one of the 

 most important families in a hygienic aspect, is connected with exhala- 

 tions of carbonic acid, which are in turn one of the most remarkable 

 phenomena of the globe's interior economy. The emanations of car- 

 bonic acid, as well as the springs to which they give character, are 

 m^ost commonly grouped near volcanoes, active or extinct, and ancient 

 volcanic rocks, basalts, and trachytes. The granitic table-land of cen- 

 tral France, in the chain of the Puys, as in the masses of Mont-Dore, 

 the Cantal, and the Vivarais, exhales daily torrents of the gas, either 

 dry or in solution, from more than five hundred springs. There are 

 Royat, with its tumultuous ebullition. Saint- Allyre at Clermont, Saint- 

 Nectaire, where all the oozings of the ground, even the road-ditches, 

 boil with gas. Disengagements of carbonic acid are frequent in the 

 mines of Pontgibaud, which are situated on the side of a crater and 

 an ancient lava-flow, and where veins of silver-bearing lead-ore furnish 

 conduits for the asphyxiating gas. 



Countries where the volcanic rocks do not aj^pear on the surface, 

 but which are broken by deep dislocations, may also be the seat of ex- 

 halations of carbonic acid. The gaseous springs of Pongues, and some 

 others of the Nievre, are situated upon simple faults. In northern 

 Germany, on the left bank of the Wescr, the country is riddled Avith 

 fractures which give passage to abundant disengagements of carbonic 

 acid, especially upon the plateau of Paderborn, and in the neighbor- 

 hood of Pyrmont, Disburg, and Meinsberg. Acid springs occur under 

 nearly the same conditions of stratification as the warm springs of 

 which we are about to treat ; and, like them, they reach the surface 

 with the assistance of quartz or other mineral veins. 



Sometimes the carbonic acid is abundant enough to make the 

 waters in which it is incorporated spurt up violently ; as at Montrond, 

 Loire, where the intermittent eruptions from a depth of five hundred 

 metres attain a great height ; and at Nauheim, in Yeteravie, where a 



