Ox the Estimation of Organic Phosphorus 173 



To avoid these sources of error, several other oxidizing agents 

 were tried in the hope that a lower temperature for oxidation 

 might be used. Redistilled 30 per cent, hydrogen peroxide was 

 finally chosen. (I am indebted to Dr. I. Greenwald for bring- 

 ing this reagent to my attention). The material is oxidized in 

 a large test tube covered with a watch glass, with 8 drops of 

 sulphuric acid and 0.2 c.c. of the peroxide. Additional hydrogen 

 peroxide is added if necessary — two or three drops at a time. 



From this point various methods may be used for the esti- 

 mation. We have proceeded as follows : The contents of the 

 tube are washed into an evaporating dish and concentrated on a 

 water bath until most of the water is removed. The solution is 

 then transferred to a graduate and the phosphorus estimated ac- 

 cording to the colorimetric process of Bell and Doisy. 



For estimating lipoid phosphorus of blood, the Bloor extrac- 

 tion has been used while other tissues have been dried with 

 plaster of Paris and extracted with ether and alcohol. 



No difficulty has ever been experienced in securing complete 

 recovery from pure phosphate solutions by the proposed process. 

 A comparison of results obtained by this method and by that of 

 Bell and Doisy with inorganic phosphate solutions and tissue 

 extracts follows : 



Proposed method. Bell and Doisy. 



1 mg. sodium phosphate 1.01 mg. 0.93 mg. 



0.2 mg. sodium phosphate 0.20 mg. 0.16 mg. 



Tissue Extract A 0.31 mg. 0.30 mg. 



B 0.36 mg. 0.34 mg. 



C 0.28 mg. 0.24 mg. 



I) 0.15 mg. 0.14 mg. 



E 3.02 mg. 2.62 mg. 



F 1.50 mg. 1.35 mg. 



It should be added that precautions must be observed in re- 

 distilling hydrogen peroxide; the distillation is done under dim- 

 inished pressure and the distillate protected from coming in 

 contact with rough surfaces or organic matter. 



All glassware must be very carefully washed with distilled 

 water and all reagents except the carbonate-sulphite solution 

 must be tested to be certain that they are phosphate free. 



