1824.] Mr. Grafs Reply to the Editor. 125 



slip of my own ; for here after you had twice copied from my 

 book the symbol for phosphorous acid, P l , as being a product 

 of this experiment, you assert, within the compass of only six 

 lines, that I have taken no notice of its production. Nor is this 

 all, for you go on to say I have not even hinted at the decompo- 

 sition of the water. Is it possible that the Editor of the Annals 

 of' Philosophy can be unable to read a chemical theorem 

 expressed in symbols 1 Upon no other ground can this censure, 

 and the one hitherto passed of my not knowing the difference 

 between iodic and hydroiodic (for so I shall continue to spell it) 

 acids, be explained. The two formulae I have given in symbols 

 express two theories of this experiment. The first I 3 , P chang- 

 ing into I' 2 , P 1 expressing that of Berzelius, in which iodine, I s , 

 is considered as a superoxide of iodinum containing three 

 charges of oxygen, which, being acted upon by phosphorus, P, 

 a simple body transfers one charge of its oxygen to the phos- 

 phorus, forming phosphorous acid, P 1 , while the iodine having 

 of course only two charges of oxygen left united with it, is 

 changed into the iodic acid, P, of Berzelius, not of Gay-Lussac : 

 in this theory, the water is passive. The other formula I, P, H 1 , 

 changing into I H, P 1 expresses the theory of Gay-Lussac. 

 Here iodine, I, and phosphorus, P, are both considered as sim- 

 ple bodies, and the water, H 1 , is active in the experiment, and is 

 indeed decomposed, its hydrogen, H, uniting with the iodine 

 and forming hydroiodic acid, I H, while its oxygen J- being thus 

 set free unites with the phosphorus and forms phosphorous acid, 

 P l . By this developement of the symbolic formulae, how little 

 cause there was for your censure is evident. As these experi- 

 ments on iodine are of no use in pharmacy, I should not have 

 mentioned them at all, leaving them to the pure chemists to 

 detail ; but that there existed a wide difference between the 

 views which Berzelius and Gay-Lussac have taken of the subject. 

 It was this slight connexion between them and the professed 

 object of my work, which caused me to express these incidental 

 matters in symbols, partly as an exercise to the student, and 

 partly because Berzelius's opinions on iodine, as detailed in the 

 Annals of Philosophy, have not been noticed in any of our ele- 

 mentary treatises on chemistry, and I was anxious that they 

 might be brought forward. 



As to the use of the term hydroiodic acid, instead of hydrio- 

 dic, it may surely be justified by this single observation. The 

 union of hydrogen with chlorine produces, according to Gay- 

 Lussac's nomenclature, the hydrochloric acid ; with sulphur, the 

 hydrosulphuric acid ; — with tellurium, the hydrotelluric acid ; — 

 with cyanogen, the hydrocyanic acid ; — with phthore, the hydro- 



Imthoric acid ; so strict analogy requires that the union of 

 lydrogen and iodine should produce the hydroiodic acid, and 

 our own language is not so rich in vowels that we can afford to 



