334 
Mr. Hatchett’s Analysis of 
acid are saturated with pot-ash or soda, they assume a very 
deep blue colour at the moment of saturation. The molyb- 
dsena is not, however, precipitated in the form of the blue 
oxyde, but for the greater p^rt remains combined with the 
acid menstruum and the alkali, and thus forms a triple salt in 
solution, which differs considerably from another triple salt, 
which is slowly precipitated at the time of saturation in the 
form of a white flocculent matter, and is composed of the same 
three ingredients, but contains the oxyde in the largest pro- 
portion. 
Sometimes a fourth ingredient becomes added to the last 
mentioned white precipitate ; for when iron is present in the 
sulphuric or muriatic solutions, it is precipitated by pot-ash 
or soda intimately combined with the other ingredients, and 
appears to render the decomposition of the precipitate very 
difficult. 
Although the triple salt which is in solution will pass 
many folds of paper without leaving any residuum, yet it is 
not permanent ; for by repeated evaporations, the neutral salt 
resulting from the combination of the acid menstruum and the 
alkali becomes crystallized, and a white flocculent matter is 
separated, which does not contain iron like that which was 
precipitated when the acid solution was saturated with the 
alkali, but can be converted into the yellow molybdic acid by 
being distilled with nitric acid, which takes from it. the small 
portion of the acid menstruum and the alkali required to con- 
stitute the triple salt. 
It has already been observed, that nitric acid has not any 
effect when immediately digested on molybdic acid, but I 
have found it otherwise when a third substance was present ; 
