GEOLOGY. 14 



;- 



almost always assailed by calumny, and who are 

 sometimes borne down by ingratitude, may in con- 

 sidering the benefits which they have rendered to 

 the human race, confidently appeal to heaven for 

 their reward, and to posterity for their justifica- 

 tion. 



LETTER XXXIV. 



Western Region, August, 1820, 

 My Dear Sir, 



Although my luggage is small, yet I never 

 travel without a blow-pipe, and some tests and re- 

 agents. If in want of any of the usual acids to 

 detect the presence of lime, I substitute strong 

 vinegar, which will generally produce an efferves- 

 cence, when poured on a calcareous substance. 

 If I am desirous of ascertaining the existence of 

 an alkali, or an acid, I stain paper with the petals 

 of a blue flower, and dip it in the water which is 

 to be tried, and if it turn green, it indicates an al- 

 Itnline impregnation, and if red an acid one. If 

 silver becomes black whei rown into water, it 

 denotes that sulphur is held in soluti >n, 

 presence of iron is de«i ous irk 



of oak give water a < p e. V. 



