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extraction with a suitable solvent. In this way a yield of 0*2 to 0*5 

 per cent, is usually obtained. Of all the constituents of the hop cone 

 probably none has been the subject of so many misstatements and of 

 so much misconception as the volatile oil. Not only were the early 

 statements in regard to its composition incorrect in nearly every 

 respect, but the role it plays in the brewing process was for long 

 entirely misunderstood. 



The oil obtained by the above method is a colourless or pale 

 yellow mobile liquid, possessing a fragrant and characteristic odour, 

 and a slightly burning taste. It is almost insoluble in water (to which, 

 however, it communicates its smell), and is only slightly soluble in 

 dilute alcohol. It appears to have been first studied by PAYEN and 

 CHEVALLIER in 1822, who obtained it by distilling the lupulinic grains 

 with water. 



In 1853, WAGNER submitted the oil to examination, and stated 

 that it contained " a terpene " and an oxygenated constituent 

 " valerol." In 1854, PERSONNE endeavoured to obtain information in 

 regard to the nature of the constituents of this oil by fractionally dis- 

 tilling it, but without much success. In 1883, OSSIPOW studied the 

 oxidation products yielded when chromic acid is allowed to act on the 

 oil and identified acetic and isovaleric acids. 



All the above investigations were made by highly competent 

 chemists, but it was in the nature of things impossible that much 

 exact information should be gained by them owing to the fact that 

 most of the compounds occurring in essential oils were then unknown, 

 that great and important branch of organic chemistry which deals 

 with the terpenes and their derivatives being of quite recent birth. 

 The admirable and masterly contributions made to this department of 

 chemical science by WALLACH and his colleagues induced me some 

 years ago to undertake a study of the essential oil of hops in the light 

 of this modern knowledge, and with the help of the more refined 

 methods which are now at our disposal. In the course of this investi- 

 gation, the completion of which has, owing to unforeseen cir- 

 cumstances and the pressure of other affairs, been considerably 

 delayed, I have worked with seven different samples of oil, and it 



