158 Fossils. 



imported it) from camels' dung ; but 

 now from bones by distillation. 



All Acids appear to be combinations of 

 oxygen or vital air, with elementary sub- 

 stances. Their taste is sour, as their 

 name imports. They change most of 

 the blue vegetable colours red, and have 

 a tendency to combine with earths, alka- 

 lies, and metallic substances. 



All acids, being compounds of oxygen 

 with different substances, the former prin- 

 ciple is the cause of their resemblance and 

 common properties ; the latter, being 

 different in each, may serve to character- 

 ize each in particular. For this reason 

 those matters which are variable in acids 

 are termed their radicals, or acidifiable 

 principles. Thus all acids are combina- 

 tions of radicals, or acidifiable substan- 

 ces, different in each species, with oxy- 

 gen, which is the same in all : whence it 

 follows, that their common properties, 

 their characters as acids, depend on oxy- 

 gen, which is the acidifying principle ; 

 their particular properties, their specific 

 characters arise from their radicals. The 

 word acid, indicating the general and 

 identical nature of these substances, forms 

 their generical name, while the particular 



