174 



decayed vegetables in summer ; yet most authors speak of 

 it as only found in the neighbourhood of volcanoes. This is 

 not the case in Wales. 



It is so well known in housewifery that it hardly requires 

 identifying: I, however, add a part of Kirwan's description. 

 Its colour is yellowish with some shade of green ; it 19 

 found concrete or in loose powder; by friction emits a pe- 

 culiar odour*, and becomes electric; heated to 170° Fahr. 

 it generally evaporates ; melts at 1 85°, and then appears red j 

 it flames of a bright blue at 302°, emitting a sharp or pun- 

 gent odour when it absorbs the pure air of the atmosphere, 

 causing a stifling sensation, and becomes acidified, forming 

 Sulphuric Acid; in close vessels it sublimes without much 

 alteration. 



* Pretty well known. 



TAB. CXCI. 



When I first visited the Isle of Dogs, atBlack\vall,Ithoughf 

 it would be interesting to observe and collect the strata as 

 belonging to a certain level pretty well determined by its 

 vicinity to the Thames. Among other subjects it was both 

 beautiful and interesting to observe the Sulphur forming on 

 the old stumps of the trees that were found from nine to 

 eighteen feet below the common level of the place ; and 

 perhaps it is no less remarkable that a stratum of leaves, 

 which was in some places three or more feet thick, had a 

 strong odour of Sulphur; but the Sulphur in general formed 

 Sulphate of Lime, or Gypsum, with the little Lime among it, 

 sparkling in the sun like minute diamonds. The same 

 occurred sometimes upon the stumps of trees; but in some 



