Natural History. 405 



hood of the cascades formed by the river, experience a smarting 

 and pain in the eyes from the effect of the minute spray in the 

 air. The analysis, by M. Rivero, of this water, gave per litre 

 (2.113 pints), sulphuric acid 16.68 grains; muriatic acid 2.84 

 grains ; alumine 3.7 grains ; lime 2.47 grains, and some indication 

 of iron. The presence of muriatic acid, says M. Rivero, confirms 

 the observations made on the vapours and stony productions of 

 Vesuvius and other volcanoes. Other sources of similar water 

 occur in the neighbourhood, which have been called the small 

 vinegars. The specific gravity of the water of the larger river was 

 1.0015. 



The volcano of Purace is a dome of semivitreous trachyte, of a 

 bluish gray colour and conchoidal fracture ; it rises from a syenitic 

 porphyry including common felspar, which in turn is superposed on 

 transition granite abundant in mica. The volcano has not a large 

 crater but many small mouths. On ascending it, and just 

 upon the limit of perpetual snow, it was observed that the sulphur 

 which occurred disseminated in the trachyte rock was increasing. 

 Further on, a column of yellow smoke, and a fearful noise indicated 

 the neighbourhood of one of the mouths of the volcano. It was 

 difficult of approach in consequence of the steepness of the moun- 

 tain and the occurrence of cracks covered only by a crust of 

 sulphur, the thickness of which was unknown : the extent of the 

 crust was estimated at 12,000 square feet. 



The mouth of the volcano was a perpendicular opening, six 

 feet long and three wide. It was covered by a crust of very pure 

 sulphur in the form of a vault, eighteen inches in thickness, which 

 the elastic vapours had broken open on the northern side. At the 

 distance of twelve feet the warmth was agreeable, the thermometer 

 rising to 60" F. nearly. The noise heard near this opening is 

 almost always of the same intensity, and may be compared to that 

 of many steam engines, the valves of which have been suddenly 

 opened. By throwing stones, it was found, that within the crevice 

 was a basin of water in ebullition. The vapours which escaped 

 with so much violence were sulphurous acid, and it was soon found 

 that the waters of the subterraneous lake were saturated with sul- 

 phuretted hydrogen. M. Humboldt had no means of determining 

 the temperature of the vapours, but they appeared to be subject to 

 extreme pressuie in the interior of the volcano. 



After several attempts, some water was obtained from the basin ; 

 it exhaled a strong odour of sulphuretted hydrogen, was not acid to 

 the taste, and was slightly precipitated by nitrate of silver. The 

 crust of sulphur over llie basin is considered as produced by the 

 mutual decomposition of the sulphuretted hydrogen and sulphurous 

 acid. The water itself was observed covered by a film of sulphur. 



Hence it appears, that the waters of this and other similar lakes 

 on the volcano, have no analogy with the water of Vinegar river, 

 except in the presence of a snjuU quantity of muriatic acid ; the 



