184 C. Fairbanks — Determination of Phosphorus in Iron. 



The more convenient way, and after a little practice a ser- 

 viceable method for rapid work, is to put the solution and the 

 tartaric acid in a bottle, to add enough sodium hydroxide to 

 nearly neutralize the free acid, and then to make the solution 

 distinctly alkaline with an excess of acid sodium carbonate, 

 tipping the flask to one side to prevent loss during the effer- 

 vescence. The iodine solution must be drawn in immediately 

 or atmospheric oxidation will take place and the error of the 

 process be great. 



After either method of neutralization the iodine color in the 

 solution should perceptibly fade within fifteen minutes ; but 

 for complete oxidation the corked bottle should be set aside, 

 out of sunlight, for an hour and a half, and then the excess of 

 the iodine titrated with a standard solution of arsenious acid. 



Since there is a slight tendency on the part of the iodine, 

 especially when the sodium hydroxide and the acid sodium car- 

 bonate are used for neutralization, to form a little iodate, it is 

 wise to acidulate the solution in each case slightly with dilute 

 hydrochloric acid after the titration with the arsenic solution, 

 and then to determine by sodium thiosulphate the trace of 

 iodine which has taken the form of iodate. 



In the following table the absolute errors in terms of phos- 

 phorus are given ; and the percentage errors, between the phos- 

 phorus taken and the phosphorus found, referred to 10 grams 

 of material — the maximum amount of high grade iron or steel 

 usually taken for analysis — are also added. 





Am't of P 



Am't of P 











taken. 



found. 



Error on P. 



% Error of P. 



Neutralized by 



I 



002727 



0-002778 



0-000051 + 



0-0005 % + 



NaHCOs 



II 



0-001812 



0-001743 



000069- 



0-0007 %— 



NaOH + NaHC03 



III 



0000909 



0-000914 



0-000005 + 



0-00005^ + 



NaOH + NaHCOa 



IV 



0-003508 



0-003262 



0-000246- 



0-002 %- 



NaOH + NaHCOa 



Y 



005454 



0005417 



0-000037- 



00003 %- 



XaHCOs 



VI 



0-001818 



0-001861 



0-000043 + 



0-0004 % + 



NaOH + NaHCOs 



VII 



0-003636 



0003716 



0-000080 + 



0-0008 % + 



NaHCOa 



^III 



0-000909 



0-000988 



0-000079 + 



0-0007 ^ + 



NaHCOa 



IX 



0-000363 



0-000289 



0-000074- 



0-0007 %- 



NaOH + NaECOs 



X 



0008180 



0-008179 



0-000001- 



0-00001^- 



NaHCOs 



The error in lY is obviously high, and, in view of the results 

 obtained in the former paper to which reference has been 

 made, undoubtedly accidental ; but the result is inserted in the 

 series because no reason was apparent for excluding it. 



In all of the experiments, with one exception, from four to 

 five grams of pure iron oxide were introduced ; in experiment 

 IX the amount was 2*5 grm. 



In the first nine experiments, 0*5 grm. of potassium iodide 

 was used ; in experiment X more was theoretically necessary 

 and 0*75 grm. was added. 



