06 Proceedings of the Royal Irish Academy. 



and H 3-4:8, and with which our analyses are not in good agreement. The 

 general reactions of our substance, however, agree in every detail with those 

 described by llesse and by Zopf for salaziuic acid. Further, Zopf (Liebig's 

 Annalen, 352 (1907), pp. 1-44), by the action of acetic anhydride on salazinic 

 acid obtained a compound, which he named salazinaric acid, which melted at 

 206-207° C. ; and on repeating this experiment with our substance a crystal- 

 line compound was obtained, which, on recrystallization from alcohol, melted 

 at 205-206° G. 



In deciding between the two types of formula for salazinic acid — one 

 corresponding to a high molecular weight, such as that of Hesse, and one 

 corresponding to a low molecular weiglit, such as that of Zopf — the main fact 

 that lends weight to the latter type of formula is that Zopf found the 

 molecular weight of salazinaric acid in benzene solution to agree with the 

 formula CjiHieO,,, which is that of a mono-acetyl derivative of a compound 

 CisHuOi,,. For this reason Zopf concluded that the high molecular weight 

 formula of Hesse could not be correct. It is, however, tacitly assumed here 

 that the salazinic acid, when acted upon by acetic anhydride, simply acety- 

 lates without undergoing any other change — an assumption which is not 

 altogether justified, considering the susceptibility of salazinic acid towards 

 reagents. Nevertheless, it was deemed advisable to consider formulae based 

 on the low molecular weight of salazinaric acid, all the more so as, owing to 

 the very slight solubility of the salazinic acid, a reliable determination of the 

 molecular weight could not be made. On the assumption of a low molecular 

 weight, the analyses obtained for our substance agree well with the formula 

 CitHuOs, which requires C 56'29 and H 3'86 ; this formula requiring a 

 molecular weight of 362, that demanded by the formula CioHnOiu being 402. 



Salazinic acid has not, up to this, been found in Parmelia saxatilis Ach. ; 

 whereas another substance, similar to salazinic acid, namely protocetraric or 

 fumaroprotocetraric acid, has been mentioned as occurring in this lichen. 

 Thus Hesse (Journ. f. pr. Chem. (2, 62 (1900). pp. 430-477) states that 

 Parmelia saxatilis var. i^anniformis Ach. contains atranorin, protocetraric 

 acid, and the so-called stereocaulic acid (Usnetinic acid) ; and again (Journ. 

 f. pr. Cheni. (2) 68 (1903), pp. 1-71), he states that I'armdia saxatilis var. 

 retiruga Th. Fr. (identical with Parmelia saxatilis Ach.), contains atranorin, 

 protocetraric acid, and saxatic acid CjsHioOs (melting at 115" C, easily soluble 

 in acetone, ether, and alcohol). 



This protocetraric acid is in more recent papers termed by Hesse fumaro- 

 protocetraric acid, the name protocetraric being given to a derivative of 

 fumaroprotocetraric acid (Journ. f. pr. Chem. (2) 70 (1904), pp. 449-502). In 

 its general behaviour it resembles our substance very closely, but differs from 



