of Molybdenum and some of its Compounds. 429 



Salts of Baryta. 



Molybdic acid forms a long series of salts with baryta, which 

 are crystalline, amorphous, soluble and insoluble. Their pre- 

 paration is in most cases easy, the corresponding baryta salt 

 being precipitated from a solution of any salt of potash or 

 ammonia. But a remarkable circumstance occurs in this re- 

 action, viz. the precipitated salt is always contaminated with 

 small quantities of the potash or ammonia salt employed, 

 which admixture cannot be removed by washing with boiling 

 water. The amount of these foreign admixtures is so small, 

 that were we to consider these salts as double salts, we should 

 be compelled to admit a most peculiar class of combinations, 

 in which one atom of the one salt would be combined with a 

 very large number of atoms of the other salt. 



This circumstance is of serious inconvenience in the analyses, 

 as the numbers found never agree accurately with the cal- 

 culated composition of the pure salt. Besides this uncertainty 

 there is another evil, arising from the great difficulty of com- 

 pletely decomposing the baryta salt. We adopted the fol- 

 lowing method for the analysis of these compounds : — We first 

 determined the loss which the salt experiences at a red heat. 

 This loss is water, but if an ammonia salt had been employed 

 for the precipitation, water and oxide of ammonium. The 

 residue was then treated in a beaker with an excess of dilute 

 sulphuric acid and evaporated, so that, eventually, the highly 

 concentrated sulphuric acid acts upon the salt. It was left in 

 this state from two to three days upon the sand-bath, then 

 diluted with water, filtered, the precipitate treated several 

 times with hot water and a few drops of sulphuric acid, the 

 precipitate placed upon the filter and washed with hot water. 

 In the calculations no attention has been paid to the small ad- 

 mixture of foreign salt, and on that account less baryta will 

 be found in all the analyses than theory requires. 



Neutral Molybdate of Baryta, Ba O, MoO 3 . — When a solution 

 of chloride of barium is added to any solution of molybdic 

 acid in an excess of ammonia, this salt instantly separates. 

 It should be filtered immediately, in order that the free baryta 

 in the solution may not absorb carbonic acid from the air 

 and accompany the precipitate. We proceeded as follows to 

 be certain of obtaining a pure salt : — 



I. A solution of the neutral molybdate of ammonia was pre- 

 cipitated with chloride of barium, the precipitate collected 

 upon a filter and washed for a very long time, although the 

 salt is somewhat soluble in water. 



II. A solution of the above-described double salt was mixed 



