rhe reaction with iodol, first described by Hirschsohn in 1893, can 

 also be used for the detection of small amounts of cineol. The 

 determination may be made by dissolving in a small quantity of 

 the oil as much iodol as it will readily take up, gently heating if 

 accessary. After a short time, if cineol be present, a crystalline 

 compound will separate; this addition product consists of equal 

 molecules of the components, and when recrystallised from alcohol 

 or benzene melts at about 112 C. 



(c) A crystalline compound is formed with cineol, when dry hydrobromic 



acid gas is passed into a mixture of the well-cooled oil, or most 

 suitable fraction, and an equal volume of petroleum ether; the 

 crystals are filtered off and washed with petroleum ether. This 

 hydrobromide melts at 56-57 ° C. and is readily decomposed into 

 cineol and hydrobromic acid on the addition of water. 



(d) Cineol also combines with gaseous hydrochloric acid, with iodine, 



with a and /3 naphthols, as well as with phosphoric and arsenic 

 acids, and resorcinol. 



THE PHOSPHORIC ACID COMPOUND. 



Cineol forms a crystalline compound with phosphoric acid of specific gravity 

 about 175, and this reaction is taken advantage of for its detection, as well as 

 for its quantitative determination. It is not a satisfactory reagent, however, 

 when only a small quantity of cineol is present in the oil, and even if containing 

 as much as 20 or 30 per cent, it is often necessary to start the crystallisation by 

 the addition of a minute crystal of cineol phosphate, prepared with a richer oil, 

 and to use an ice cold bath. The combination between the cineol and the 

 phosphoric acid is a very loose one, and even at room temperature the compound 

 slowly changes with separation of cineol. 



The reddish colouration given to Eucalyptus oils by phosphoric acid when 

 cineol is tested by this method, is caused by the reaction between the acid and 

 the sesquiterpene, a constituent which occurs in most Eucalyptus oils, sometimes 

 in considerable quantity. In the oils of some species, however, it is present in 

 very small amount, as for instance in those of the group to which E. Australiana 

 belongs, so that in the oils of those species the colouration is usually somewhat 

 indistinct. This is also the case when the oils have been rectified by direct 

 distillation, as in this way the greater portion of the sesquiterpene, or other 

 high-boiling constituent, mostly remains behind in the still, so that the 

 colouration is not shown so distinctly as with the crude oils. The selective 

 influence of cineol for phosphoric acid does not however take place, and the 

 appearance of the pink colouration may thus be deceptive if considered as an 

 indication of the end reaction. 



It has been considered, and is often so stated, that the cineol and 

 phosphoric acid enter into combination in molecular proportions ; thus forming 

 a solid compound with a definite composition. Helbing and Passmore (Phar- 

 macological Record No. XXXV) describe this method for determining cineol, 

 and assume the following equation : — C IO H l8 + H 3 P0 4 = C IO H lS OH 3 P0 4 , in 

 which the cineol represents 61 -i per cent. 



The question is, however, does the phosphoric acid enter into combination 

 with the cineol in molecular proportions, or does it combine in the form in which 

 it is used? If the latter, then the statement that the compound contains 61 -i 

 per cent, of cineol is not correct. 



We have endeavoured to solve this problem, with the result that our 

 investigation shows that the phosphoric acid, specific gravity about 1-75, combines 



