212 ESSAY XIX. 



having been edulcorated with water, was put into another 

 phial, (d) On this yellow powder I poured 8 scruples 

 of caustic volatile alkali, and exposed the phial to heat; 

 the yellow colour presently vanished, and the powder became 

 white. This solution was then in like manner poured into 

 a separate flask, and the powder edulcorated. As the matter 

 was sensibly diminished by these operations, I repeated them 

 many times on the same powder, digesting it first in the 

 nitrous acid, and then in the volatile alkali, till at length 

 the greatest part of it was dissolved. What remained un- 

 dissolved weighed 3 grs., and seemed to be siliceous earth. 

 Muriatic acid produces the same effect upon tungsten as the 

 nitrous, but the solution was of a deeper yellow. 



SECTION III. 



(a) The solutions made in the foregoing manner with 

 the nitrous acid being all mixed together, some drops of 

 phlogisticated alkali were added, upon which about 3 grs. of 

 Prussian blue were precipitated, (b) The mixture was then 

 saturated with caustic volatile alkali ; but as no precipitate 

 appeared, some solution of alkali of tartar was added ; a white 

 powder now fell to the bottom, which, when washed and 

 dried, weighed 2 scruples and 5 grs., and was found to be 

 aerated lime unadulterated ; so also is the earth obtained 

 (Sec. I. (#)). (c) The extracts procured by volatile alkali were 

 precipitated with nitrous acid ; the precipitate was washed 

 with cold water and dried ; it is exactly the same as that 

 mentioned in Sec. I. (/). (d) It is of an acid nature, not 

 easily soluble in water, for near twenty parts of boiling water 

 are required to one of the precipitate ; it colours the tincture 

 of litmus red, and has an acid taste. 



