Prof. Johnston on the Iodide of a ?iew Carbo-hydrogen, 7 



attention has recently been recalled to the subject by a paper 

 on Hellenine, by M. Gerhardt (Ann. de Chim. et de Phi/s. 

 vol. lxxii. p. 163), in which he gives for this substance the for- 

 mula C 15 H 10 2 or C 30 H 20 4 , containing apparently a ra- 

 dical isomeric with the carbo-hydrogen C 30 H 20 , which exists 

 in the iodide above described. By the action of chlorine, hel- 

 lenine becomes (C 15 H 10 O 4 + C 15 H 10 C1 4 ) according to Ber- 

 zelius, or (C 15 H 9 CI 2 + H CI) according to Dumas, in 

 which we see a considerable analogy with the formulae for 

 the oxichloride above described. By the action of anhydrous 

 phosphoric acid on hellenine, a yellow liquid carbo-hydrogen 

 is produced, to which M. Gerhardt gives the name of hel- 

 lenene, and which is represented by the formula C 15 H 8 , -r- 

 the hypothetic radical which enters into the constitution of 

 our oxichloride as it is represented in the formula (4). 



These interesting approximations indicate a series of com- 

 parative experiments, to which the iodide described in the 

 present paper might be subjected, with the hope of throwing 

 new light on the nature of the ever-varying isomeric modifi- 

 cations, of which the compounds of carbon and hydrogen are 

 susceptible. I hope to be able soon to return to the subject 

 with a view to this investigation. 



In regard to the presence of a carbo-hydrogen represented 

 by the formula C 30 H 20 in coal gas, it need not excite our 

 surprise if many other such compounds should hereafter be 

 met with among the volatile and gaseous products obtained 

 from the distillation of coal. When we consider how many less 

 volatile substances of this class have been extracted by Pelle- 

 tier and Walter* from the products of the distillation of resin 

 for the manufacture of gas, and how many more volatile ones 

 have been separated by Couerbef from the gas thus produced 

 when subjected to pressure, we shall be prepared to expect 

 in coal gas also, the vapours of many other volatile substances 

 in addition to those which have hitherto been detected. 



I have not as yet proposed any name for the supposed 

 radical C 30 H 20 . It belongs to the same group as mesitylene 

 (Enyl of Berzelius) =s C 6 H 4 and retinyle C 18 H 12 , in both 

 of which the elements are in the ratio of 3 to 2. It would 

 be exceedingly desirable to adopt the system of nomenclature 

 proposed by Berzelius for these compounds, in which the name 

 is compounded of the Greek numerals expressive of the num- 

 ber of atoms of each element which are contained in the 

 compound. But that such names may be univerally adopted, 

 it is necessary that the same atomic weights should also be 



* PoggendorfTs Annalen, vol. xliv. p. 81. 

 t Ann. de Chim. et de Phys.> vol. lxix. p. 148. 



