92 HOT SPRINGS, ARKANSAS. 



Gases. — The gases given off by the hot waters were carefully col- 

 lected and analyzed. The results show that they consist of carbon 

 dioxide, oxygen, and nitrogen. The ratio of oxygen and nitrogen 

 corresponds very closely to that of atmospheric air, and, taking into 

 account the relative absorption of the two gases by water, there can be 

 no doubt that the oxygen and nitrogen given off by the water come 

 from absorbed air. 



Source of water. — From what has already been said in discussing the 

 geological and topographical relations of the springs, and from the 

 composition of the water and of the gases, there seems no doubt that 

 the hot springs correspond closely to the ordinary springs of the 

 mountain region save in the very important element of heat. As will 

 be shown later, it is believed that the waters of a very large but 

 entirely normal spring, or springs, have been heated by vapors rising 

 through fissures penetrating its unknown depths. 



Source of mineral contents. — The mineral matter of the waters has 

 come from the rocks traversed by the waters. Recollecting the solvent 

 power of hot water, it is rather remarkable that the waters are so pure. 

 The undertying rocks are Silurian sediments resting on an unknown 

 complex, but the Silurian rocks alone are competent to supply all the 

 mineral matter of the waters. 



ARE THE HOT SPRINGS DYING? 



The question whether the hot springs are changing in character 

 and will eventually either cease flowing or become cold springs 

 is of both popular and scientific interest. The evidence seems to 

 show that there is a very small decrease in temperature since the} T 

 were first examined, now nearly a century ago. The temperature 

 recorded by Dunbar and Hunter in 1804 for the larger spring was 150° 

 F., and another had a temperature of 154°. In 1859 the springs were 

 carefully examined by David Dale Owen, State geologist, whose map 

 of temperatures and elevations is reproduced in Plate VIII herewith. 

 A more accurate map was published by William Glasgow, jr., in 1860 

 from careful instrumental surveys, together with records of temper- 

 ature and outflow. 



Since then many changes have been made about the springs, all of 

 which have been dug out and inclosed in masonry arches, with the 

 consolidation of two or more springs into one in some instances, the 

 development of new outflows b} T digging wells or sinking pipes, and 

 the drying up of adjacent natural outflows. For these reasons all the 

 springs now existing can not be positively identified with those shown 

 on the earlier maps, but a majority of them are so correlated without 

 doubt. 



Temperatures.- — The comparison of the old records mentioned with 

 those recently made shows that the highest temperature known to-dav 

 is 117° F., as against 151° in 1804, and 150° by Glasgow and 148^ by 

 Owen in 1860. In a number of springs there is a decline of 2° since 

 the latter date. Such a slight difference might, however, be due to 

 differences in the manner or place of taking the temperatures, or the 

 instruments used in the earlier } T ears ma} 7 not have been accurate. It is 

 noteworthy that Owen's highest temperature, taken in 1859 with a 

 standardized thermometer, was 148°, and that recorded now is 147°. 

 In other words, the temperature is decreasing so slowly that the change 



