70 F. B. GUTHRIE AND A. A. RAMSAY. 



A method published by Gerhardt 1 was also investigated, 

 but gave very unsatisfactory results. The method depends 

 upon the formation of superphosphate when calcium car- 

 bonate is neutralized by phosphoric acid, according to the 

 equation 2 H 3 P0 4 + CaCC^ETsO + CaH 4 (P0 4 ) 2 + 00 2 

 This reaction is not, however in accordance with observed 

 facts. The method will be made the subject of further 

 investigation before a decided opinion is expressed upon it. 



Herzfelder 2 finds that none of the processes in use are 

 trustworthy and suggests a new one based on the facts 

 that free phosphoric acid is soluble in ether and that phos- 

 phates are not, and that monobasic phosphates are neutral 

 to methyl orange and dibasic phosphates alkaline. 



It was thought that it would be interesting to study the 

 behaviour of different indicators towards free phosphoric 

 acid and phosphates. Phosphoric acid was prepared by 

 burning phosphorus in an excess of oxygen, dissolving the 

 pentoxide formed in water, evaporating and drying in a 

 desiccator under diminished pressure. 



A. 10 grammes of this phosphoric acid was dissolved in 

 1000 cc. water and 20 cc. (containing *2 grms. acid) titrated 

 with decinormal soda, using various indicators. 



B. 2 grammes of the phosphoric acid prepared as above 

 described was treated in the cold with successive portions 

 of ether (free from water and alcohol) a small amount of 

 residue was left behind. The ethereal solution was evapor- 

 ated off, water being added until the ether was expelled 

 and an aqueous solution of phosphoric acid obtained. This 

 was made up to 200 cc, and portions of 20 cc. (*2 grams. 

 H 3 P0 4 ) were titrated against N/10 NaOH, using different 

 indicators. 



1 Chem. Zeitung., 1905, Vol. xxix, p. 178. 

 2 Analyst, Vol. xxvm, No. 333, p. 372. 



