126 Mr. E. A. Parnell on the Composition qflnulin. 



The formula of sulphate of ammonia is not 4? (S 3 . N H 4 O), 

 because by heat it gives 2 (S 2 . N H 4 O) + 2 S 2 + 2 N, but 

 every property must be taken into account, and our idea of the 

 body derived from a careful induction, based on a study of all 

 the facts known of it and of its congeners. 



The red substance described by Mitscherlich resembles, in 

 fact, those obtained by Rose with sublimate and phosphuretted 

 hydrogen, and the bodies I have myself described, containing 

 arsenic. In fact, as Laurent and Bineau have noticed for 

 azote, and I myself for arsenic and phosphorus, these sub- 

 stances replace oxygen or amidogene in the proportion of one- 

 third of their ordinary equivalent. Phosphuretted hydrogen 



P H 3 does not resemble ammonia N H 3 = Ad H, but — . H 



3 



resembles Ad H or H O. The compound of iodide and phos- 

 phuret of hydrogen resembles not the hydriodate of ammonia*, 

 which is I H + H Ad, but the oxy-chloride of mercury, and 

 the compound of chloride and phosphuret of mercury is si- 

 milar. There are thus 



He* CI 4- 3 Hff — \ a ^ corres P oncun g bodies. 



HgCl + 3HgO 



Now the ammonia compounds when decomposed by heat 

 pass into this class, in one or two cases the action being suf- 

 ficiently violent spontaneously to effect it, and the substance of 

 Mitscherlich is 



N 

 2 Hg CI + 3 Hg — resembling the above. 



o 



I discovered this body myself when analysing white precipi- 

 tate ; but as I did not wish to stray from the direct discussion 

 of the amidides, 1 did not publish anything about it at the 

 time. I formed also some others of the same class, which, as 

 soon as I can obtain leisure I will complete the examination of, 

 and give the details of their history. 



XIX. On the Composition oflnulin. By Mr. E. A. Parnell*. 



THIS substance, which was first discovered by V. Rose 

 in the root of Inula Helenium, in 1804, has since been 

 found by Payen and other chemists in several other roots, as 



* Communicated by Professor Graham, 



