207, 208] Analysis of Basic Slag 131 



a-half hours. The reprecipitation in the same way wil) occupy 

 an hour. 



207. Second method, used for estimation of phosphoric 

 acid only. Should the percentage of lime not be required, the 

 weighed portion of slag (1 gram) may be dissolved in 25 c.c. of 

 strong H 2 S0 4 . This is done in a flask on a sand bath, and the 

 liquid heated until it fumes strongly. It is then allowed to cool 

 and is poured into a beaker containing 75 c.c. of water. The 

 flask is rinsed out two or three times with water. The muddy 

 liquid is allowed to settle, and filtered. The precipitate is well 

 washed, 8 grams of citric acid and excess of ammonia are added, 

 and the liquid cooled. The phosphoric acid is precipitated as 

 before by 25 c.c. of MgCl 2 mixture and excess of strong am- 

 monia. This method is not so reliable as the last, as the 

 calcium citrate has a solvent action on the precipitate, whilst, 

 on the other hand, the sulphuric acid present tends to throw 

 down a basic magnesium sulphate along with the phosphate 

 precipitate. 



208. Rapid method for the estimation of phosphoric acid. 

 For this estimation it is necessary to prepare two solutions, 

 one of ammonium nitrate, the other of ammonium molybdate. 



Ammonium Nitrate. Dissolve 100 grams in 90 c.c. of hot 

 water ; when cold, make up to 165 c.c. with distilled water. 



Ammonium Molybdate. Measure 100 c.c. of water into a 

 large flask. Add 50 grams of molybdic acid, then 100 c.c. of 

 *88o ammonia. Stir until dissolved. Pour the solution quickly 

 into a large stoneware jug containing 720 c.c. of cold nitric 

 acid (S.G. 1*20), stirring well whilst adding. Allow to stand 

 over night, and filter. 



Weigh out exactly -5 gram of the sample. Transfer to a 

 4-oz. wide-mouthed beaker, and add 8 c.c. of strong pure HC1. 

 Evaporate to dryness on the water bath, finishing on the sand 

 bath. Allow to cool ; then moisten with 8 c.c. of pure HC1, 



