PHOSPHOROUS ACIDS. 425 



any change ; owing, without doubt, to the strong cohesion of its 

 particles.* 



(/.) Phosphoric acid separates the carbonic, with effervescence, 

 from its combinations. 



4. COMPOSITION. According to Lavoisier's elaborate experiments, 

 related in his Elements, phosphoric acid is composed of about 60 

 parts of oxygen to 40 of phosphorus, f or about 3 parts of the former 

 to 2 of the latter. Other and more recent philosophers give less 

 oxygen, but differ in their results. 



Rose, 100 phosphorus are combined with 114.6 oxygen. 



Dulong, 100 do. do. 124.8 do. 



Berzelius, 100 do. do. 127.5 do. 



Davy, 100 do. do. 135. do. 



Davy formerly obtained 153. for the proportion of oxygen. Dr. 

 Henry thinks that the true -proportion is probably 133J. The com- 

 bining weight of phosphorus has been deduced from the composi- 

 tion of phosphate of lead, and is taken at 12.J and that of phospho- 

 ric acid, adding 2 equivalents of oxygen, 16, at 28. 



5. POLARITY. It is attracted to the positive pole, and is therefore 

 electro-negative. 



6. USES. A powerful acid, not known in common life nor in the 

 arts. Some of its alkaline salts are used as fluxes. 



7. DISTINCTIVE CHARACTER. The solid phosphoric acid, heated 

 on charcoal by the blowpipe, exhibits a flame, proceeding from the 

 decomposition of the acid by the coal and the consequent emission 

 and combustion of phosphorus. 



PHOSPHOROUS ACIDS. 



1. HISTORY. Lavoisier, in 1777, first demonstrated that the two 

 acids of phosphorus, obtained by the slow and by the rapid com- 

 bustion, are different compounds, owing to their different propor- 

 tions of oxygen. 



2. PREPARATION. 



(a.) Till Sir H. Davy proved the contrary, it was thought that the 

 only mode of preparing phosphorous acid, was by a slow combustion 

 in the air. At a high temperature, phosphorus, whether burning in 

 common air or in oxygen gas, is saturated with oxygen, and produ- 

 ces phosphoric acid ; at a common temperature it becomes, at least 

 in part, phosphorous acid. 



* Fourcroy, II. 69. t Corresponding, if phosphorus is 12, with 5 equiv. of each. 



t For the grounds of this conclusion see Henry, Vol. I, p. 377, 10th ed. This 

 number is not universally adopted. See Turner's Chemistry, 2d ed. p. 261, where it 

 is stated that M. Dulong conceives the oxygen in the phosphorous and phosphoric 

 acids to be in the proportion of 1.5 to 2.5 or 3 : 5, and Berzelius thinks that phospho- 

 ric acid is composed of oxygen 56 parts and phosphorus 44, (very near the results 

 obtained by Lavoisier.) 



54 



