428 PHOSPHOROUS ACIDS. 



ing. The theory will be intelligible after chlorine has been dis- 

 cussed. 



2. PROPERTIES. 



(.) Jlcid to the taste reddens vegetable blues, and forms phos- 

 phites with alkalies. 



(6.) Odor fetid give white vapors by heat combustible in the 

 air, and therefore contains an excess of phosphorus, which being ex- 

 pelled or burned, the residuum is phosphoric acid. 



3. COMPOSITION. 



Phosphorus, 56.81 100 132 



Oxygen, - 43.19 76 100 



100.00* 



Phosphorus, 56.524 100 



Oxygen, - 43.476 76.92 



lOO.f 



By a more recent investigation, Sir H. Davy concluded that 

 phosphorous acid contains just half as much oxygen as phosphoric 

 acid. Phosphorus, 59.7 100. 



Oxygen, - 40.3 67.5 



100. 



4. CONSTITUTION. Taking it for granted, that in phosphorous 

 acid, the elements are united, equivalent and equivalent, and calling 

 phosphorus 12 ; the phosphorous acid will be represented by 12 + 8 

 =20, the representative number, J while phosphoric acid is supposed 

 to be composed of phosphorus, 1 equivalent, 12, and oxygen, 2 

 equivalents, 16=28, as stated under phosphoric acid. 



The above are the views of Sir H. Davy and Dr. Thomson, but 

 Berzelius and Dulong consider the oxygen in the two acids as being 

 in the proportion of 2 to 5. 



HYPO-PHOSPHOROUS ACID. 



1. HISTORY. Discovered by Mr. Dulong^ in consequence of 

 observing the peculiar action of phosphuret of baryta upon water. 



2. PREPARATION. 



(a.) By this action, two compounds are said to be formed; an in- 

 soluble phosphate of the earth easily separable by the filter. 

 (b.) Jl soluble barytic salt which passes through the filter. 



* Gay-Lussac. t Dulong, Phil. Mag. XLVIII, 273. 



t Henry, Vol. I, p. 373, 10th Ed. Phil. Mag-. V. 48, p. 271. 



