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Scientific Proceedings (127) 



causes of error, attention was given to the ashing process, modi- 

 fications of the Neumann ashing process being used. In this 

 method, which had given satisfaction for the macro estimation 

 of phosphorus for a long time, two possible sources of error were 

 discovered. 



Although when heated alone, phosphoric acid does not 

 volatilize until a temperature of about 260° C. is reached, when 

 it is heated with sulphuric acid at 180°-200° C. it volatilizes 

 slowly in the vapors of sulphuric acid — a fact which the writer 

 subsequently found had been demonstrated by Hillebrand and 

 Lundell. This source of loss was found to occur both in the 

 Bloor and Bell and Doisy methods. In addition, when the lat- 

 ter method of ignition was used, some conversion of ortho to 

 pyrophosphoric acid was usually found to occur because of the 

 very small amount of sulphuric acid used. 



The fact that volatilization occurs under the conditions pres- 

 ent in the Bell and Doisy and Bloor ashing processes was dem- 

 onstrated as follows : 



One c.c. of a phosphate solution containing 1.0 mg. of P 

 was placed in the bottom of a pyrex test tube 8x1 and 

 to it were added a few washed quartz pebbles, 8 drops of 

 sulphuric acid and 1 c.c. of nitric acid as suggested by Bell and 

 Doisy, or 1.5 c.c. of a mixture of equal parts of sulphuric and 

 nitric acids as Bloor uses. The upper part of the tube was then 

 drawn out and bent at right angles and the tubes heated as in 

 the ashing processes of these authors. The vapors were collected 

 in a dish of water. The solution containing the vapors was con- 

 centrated on the water bath and the acid neutralized with freshly 

 distilled ammonium hydroxide. The amount of phosphorous 

 was then estimated in the distillate and residue. Losses of 

 from 2 to 15 per cent, were found to occur. A typical experi- 

 ment with the Bloor ignition method is given : 



Amount of phosphate used 1.00 mg. 



in distillate .07 

 " residue .94 



When the Bell and Doisy ignition method was used the sum of 

 the phosphorus in the distillate and residue was usually less than 

 the amount started with due to conversion of ortho to pyro- 

 phosphoric acid. 



