194 EXPERIMENTS ON MOLYBDENA. 



and after it was cold it resembled altogether a concentrated 

 solution of acetite of copper inclining a little to blue, in 

 other words, it was of a deep blueish green ; it Was of a 

 metallic and bitter taste ; and no precipitate was lormed. 

 The addition of a little muriatic acid appeared to restore 

 tbe original blue colour. This experiment evidently shows, 

 that the blue oxide is capable of passing to a higher degree 

 of oxidation by the effect of simple boiling in water ; and 

 that this degree of heat must if possible be avoided, when 

 we wish to obtain blue oxide. Several other experiments, 

 which it would be superfluous to detail here, taught me, 

 that the following process is best adapted to produce a pure 

 and permanent blue oxide. 

 Best process for Take one part of metallic molybdena and two parts of 

 obtaining pure -j / 4.1, ^" f u -j j r 



aadpermanent P"^6 molybdic acid \or three parts ot brown oxide and four 



blue oxide. of acid), triturate them a considerable time in a porcelain or 

 glass mortar, moistening the mixture with distilled water, 

 either at the beginning or after it is reduced to a fine pow- 

 der, so as to give it the consistency of pap. Continue the 

 trituration with a moderate heat, till the matter is very blue. 

 Then add eight or ten parts of water, and boil for a few 

 minutes. After the liquor has stood a little while, filter it, 

 and continue to triturate and lixiviate the residuum, till no 

 more blue solution is obtained. All the solutions being 

 poured into a porcelain capsule, they are to be evaporated 

 at a heat of 30° or 40° of R. [100° or 122° F.], when the co- 

 lour will undergo no sensible change, and a very fine blue 

 residuum will be obtained, which is soluble in a veiy 

 Fvawcration small quantity of water. Care must be taken, that the 

 must not be too evaporation does not go on too slowly; fori think I have 

 * '^^' observed, that in consequence of being in contact with the 



oxigen of the atmosphere, the blue oxide passed gradually 

 to gi-een, yellow, and lastly even to white molybdic acid. At 

 icast I have remarked these phenomena, when potash or am- 

 monia was present in the blue solution. 

 Means of pre- This accident however may be prevented effectually, by 

 veuting too leaving a little metallic molybdena or brown oxide in contact 

 ' with the solution evaporated, till the liquor has attained the 

 con«istence of a sirup. This will prevent the oxigen present 

 from producing a higher degree of oxidation. 



From 



