174 ESSAY XII. 



very violently in digestion, and deprives it of its phlogiston, 

 upon which it grows white, and regains its former property. 

 Vitriolic and muriatic acids have no effect upon it. 



SECTION XI. 



The earth of molybdama which is procured by nitre 

 (Sec. v.) is in several circumstances different from that just 

 mentioned. (1) It requires much more water for its 

 solution ; 2 oz. of water, dissolved by continued boiling, 

 11 1 scruples. (2) It expels not the vitriolic acid from 

 vitriolated tartar. (3) It is more easy of fusion. (4) It 

 does not sublime in an open crucible. (5) When fused with 

 charcoal powder, it affords a solution with water, containing a 

 neutral salt, which precipitates all other neutral salts. 



SECTION XII. 



The cause of this great difference lies in the alkali, of 

 which this precipitate obstinately retains a part. That it 

 contains alkali, though it be purified by repeated solutions 

 and crystallisations, is easy to infer from the following 

 experiments : (1) When to a hot solution some concentrated 

 nitrous acid is added, and the boiling continued, the greatest 

 part of the dissolved earth falls to the bottom in the form 

 of small crystals. If afterwards the clear liquor is evaporated, 

 some nitre is obtained. These small crystals have the same 

 properties with that earth of molybdaena that is procured by 

 nitrous acid (Sec. in.). (2) The salt which is obtained by 

 fusion (Sec. xi. (5)) proves the same. This neutral salt is 

 produced in the following manner : The earth which con- 

 tains only a small quantity of alkali, and yet operates like 

 an acid, because it changes the colour of lacmus to red, 



