244 ANNUAL OF SCIENTIFIC DISCOVERY. 



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pose a large quantity of the molybdate solution is prepared as follows : 

 one part of molybdic acid is dissolved in eight parts of ammonia, and 

 twenty of nitric acid. The phosphate is dissolved in nitric acid, and 

 there is added to it, a quantity of molybdic acid equal to about thirty 

 times that of the phosphoric acid. The solution with the precipitate 

 is digested for some hours with the aid of a very gentle heat, filtered, 

 and washed with the same solution which was used for the precipita- 

 tion. The whole is then dissolved in ammonia, and the phosphoric 

 acid thrown down by a magnesian salt. The presence of molybdic 

 acid is not injurious, as the double molybdate of ammonia and mag- 

 nesia is easily soluble. Sonnenschien's experiments on the separation of 

 phosphoric acid from alumina and other bases all gave very good 

 results. 



With a view of confirming this discovery, and also of ascertaining 

 with more precision the cause of the peculiar behavior exhibited by 

 this substance towards re-agents, numerous trials have been made with 

 it by Mr. Craw. Solutions of the caustic alkalies, and the alkaline 

 carbonates and phosphates, dissolve the yellow compound even in 

 the cold. So do also chloride of ammonium, and oxalate of ammonia. 

 The mineral acids also act upon it to some extent. Cold water 

 dissolves it with great difficulty, though it is soluble in hot water. It 

 appeare to be decomposed to a small extent by the combined influence 

 of air and moisture, as it turns blue when dried in the atmosphere after 

 washing with water. Its behavior towards solvents is changed by the 

 presence of molybdate of ammonia, so that it becomes nearly insoluble 

 in acids even on boiling. The act of solution is probably in all cases 

 attended with decomposition and removal of molybdic acid which is 

 prevented by the presence of molybdate of ammonia. Some quanti- 

 tative experiments were also made on the separation of phosphoric 

 acid from the bases, and the results obtained confirm those of Sonnen- 

 schein, and show that the method as regards accuracy, is all that can 

 be desired, while in point of simplicity, it is superior to any of the old 

 processes. It will prove of especia"! advantage in cases where, as in 

 the analysis of soils, a small quantity of phosphoric acid is associated 

 with a variety of other substances existing in much larger proportion. 

 It may be important to remark, that when effecting the precipitation 

 by means of molybdate of ammonia, this, as well as nitric acid, should 

 be in decided excess. To ascertain when this is the case, before fil- 

 tering off the solution, a drop of it may be transferred to a solution of 

 sulphuretted hydrogen, when a brown precipitate of sulphuret of 

 molybdenum will appear. After separating the yellow precipitate 

 from the solution, the latter should be always allowed to stand for 

 some time in a warm place, to see whether any additional precipitate 

 is formed. 



ON A SPECIAL ACID OF THE LUXGS. 



M. DUMAS recently presented a paper to the academy, giving an 

 account of his and M. VerdiePs researches on a special acid secreted 



