1 72 AGRICULTURAL ANALYSIS 



dilute sulfuric acid (i :2o). A, B, and C represent different meth- 

 ods of filtering the molybdic solution. In A a platinum cone is 

 placed in the constricted portion of the tube and the asbestos felt 

 placed thereon and the tube then filled with the granulated zinc. 

 In B there is first inserted a perforated disk, then some very fine 

 sand, and this is covered with another disk. In C there is a perfor- 

 ated disk which is covered with asbestos felt. The filtering ar- 

 rangement should be" such as to prevent any zinc particles from 

 reaching the flask and yet permitting the filtration to go on with- 

 out much difficulty. A blank determination is first made by adding 

 to 180 cubic centimeters of water 12 of 0.96 ammonia and 10 of 

 strong sulfuric acid. This is poured through the reducing tube 

 and followed with 200 cubic centimeters of water, taking care 

 that no air enter the apparatus. Hydrogen peroxid is formed if 

 air enters. Even after standing for a few moments the tube should 

 be washed with dilute sulfuric acid before again using it. The 

 filtrate should be titrated with the permanganate solution and the 

 amount required deducted from the following amounts obtained 

 with the molybdic salt. 



Calculations. The calculations of the amount of phosphorus 

 in a given sample of iron or steel are made according to the fol- 

 lowing data: 29 In a given case let it be supposed that the per- 

 manganate solution is set with a solution of piano wire containing 

 99.27 per cent, of pure iron, and it is found that one cubic centi- 

 meter of permanganate liquor is equal to 0.003466 gram of me- 

 tallic iron. It is found that 90.76 parts of molybdic acid will pro- 

 duce the same effect on permanganate as 100 parts of iron. Hence 

 one cubic centimeter of permanganate solution is equivalent to 

 0.003466X0.9076=0.003145 gram of molybdic acid. In the yel- 

 low precipitate formed, in the conditions named for the analysis 

 it is found that the phosphorus is one and nine-tenths per cent, 

 of the molybdic acid present. Therefore, one cubic centimeter 

 of permanganate liquor is equal to 0.003145X0.019=0.0000597 

 gram of phosphorus. If then, for example, in a sample of iron 

 or steel eight and six-tenths cubic centimeters of permanganate 



* Dudley and Pease, Journal of Analytical and Applied Chemistry, 1893, 

 7 : 112. 



