from Native Molyhdena. ig^ 



self, on cold bodies presented to it, under the form of nee* 

 dies and yellow scales. It appears that acidulous molybdatc 

 has often been employed lor pure molybdic acid. Thus 

 Lampadius gives reason to believe that the acid which he 

 prepared by the above process was not pure acid but acidu- 

 fous molybdate. He recommends decomposing the mass 

 which remains after deflagration by muriatic acid in excess. 

 It will be seen by the following experiments that the mo- 

 lybdic acid cannot be entirely freed from the potash. To 

 remove this ob-^tacle to the preparation of pure molybdic 

 acid, Scheele recommends dissolving the precipitate ob- 

 tained in the smallest quantity of water possible, and boil- 

 ing it for some minutes with a new quantity of nitric acid. 



When the alkali has been thus separated, the molybdic 

 acid is supposed to deposit itself in very small crystals. It 

 appears to me confirmed that in this manner there is sepa- 

 rated a little pure acid ; but the very large part of the acid 

 which remains dissolved with the acid added in excess is 

 obtained separately v.ith very great difficulty ; and whea 

 enough of acid is not added, a mixture of pure acid and acid 

 holdingr alkali is obtained. As this fourth process appeared 

 to me far preferable to the rest, being much shorter and 

 more oeconomical, I wished to try whether it was not pos- 

 sible still to improve it, and to render it common in the 

 preparation of the molybdic acid. 



As the proportion of nitre, even in the process of Four- 

 croy, appeared to me still too great, I was desirous to exa- 

 rnine whether something might not be saved in this point 

 of view. 



Experiment I. 



T heated to redness in a Hessian crucible six gros of salt- 

 petre, and projected on it, in parts, pure sulphurated moiyb- 

 dena pulverized. After I had added two gros and twenty 

 grains of this mineral, the deflagration was still very brisk. 

 I maintained the matter in fusion for some minutes longer, 

 after which 1 dissolved the mass in water. The solution 

 was complete, a few grains of oxide of iron and of silex ex- 

 cepted. On proceeding to the crystallization of the salts 

 contained in this mass, 1 obtained some small crystals of 

 undecomposed nitre. 



Erperiment II. 



According to the indication furnished by the preceding 

 experiment, I took two pv.mnds three quarters oJ' puriSed 

 nilte, which I brought to rrd fusion, and gradually pro- 

 jected ou It a pound of pulverised Bulphuret oi molybdena. 

 I^ 2 When 



