316 D. L. Randall — Behavior of Molybdic Acid. 



slowly and with constant stirring into a mixture of !00 cmS 

 of strong nitric acid (1*42 sp. gr.) and 600 cm3 distilled water. 

 Then 50 milligrams of microcosmic salt dissolved in a little 

 water are added, the mixture is agitated thoroughly, the pre- 

 cipitate is allowed to settle for twenty-four hours and the solu- 

 tion is filtered before using. 



In order to have iron present during the precipitation of the 

 phospho-molybdate, a solution of ferric nitrate was prepared 

 and used in each experiment. A solution of the C. P. 

 ferric nitrate of commerce, Fe(N0 3 ) 3 9H 2 0, was made up to 

 contain 150 grams to the liter, with enough nitric acid added 

 to give the solution an amber color. To free the iron solution 

 from traces of phosphorus, 400 cm3 of the molybdenum solution 

 were added to the ferric nitrate and the whole well shaken and 

 allowed to stand for twenty-four hours. 



To measured portions of the phosphorus solution, in a 300 cm> 

 Erlenmeyer flask, were added 150 cm3 of the iron solution fil- 

 tered and warmed to 35° C. The flask was stoppered 

 with a rubber stopper and shaken for five minutes. The 

 precipitated phospho-molybdate was allowed to settle, and was 

 then filtered on asbestos in a perforated crucible and washed 

 with a solution of ammonium acid sulphate (15 cm3 ammonia, 

 25 em3 sulphuric acid, 1 liter water). The Erlenmeyer was 

 washed out with a solution of 20 cm3 of water and 5 cm3 of 

 ammonia, and this was poured on the asbestos in the crucible. 

 The molybdenum solution was acidified with 10 cm3 of strong sul- 

 phuric acid and was passed through the reductor into the ferric 

 alum solution. The molybdenum solution was preceded by 

 100 cm3 of hot water and followed by 200 om3 of the hot dilute acid 

 and 100 cm3 of water. The reduced solution was titrated imme- 

 diately with approximately tenth normal permanganate. In 

 the following table are shown results thus obtained in precipi- 

 tating phosphorus as the phospho-molybdate, passing the acidic 

 solution through the reductor into a solution of ferric alum, 

 and titrating the ferrous salt which is formed. 



Table IV. 

 P taken P found Error 



grms. grnis. grms. 



•003645 -003673 +"000028 



•003645 -003697 +'000052 



•003645 -003638 —'000007 



•003645 -003726 +'000081 



•003645 -003630 —'000015 



•003645 '003661 +-000016 



These results are calculated on the assumption that the ammo- 

 nium phospho-molybdate contains phosphorus and molybde- 

 num in the proportion given by the symbol (NH 4 ) 3 12Mo0 3 P0 4 , 

 and that the reduction proceeds to the condition represented 

 by the symbol Mo 2 3 . 



