MEDICINAL USES OF HOPS. 25 



According to Wagner ('.Chemical Technology '), the essen- 

 tial oil, the flavouring principle of the hops, is met with in 

 air-dried hops, to the amount of 8 per cent. ; it is yellow- 

 coloured, with an acrid taste, without narcotic effect, of a 

 specific gravity = 908, turning litmus paper red. It re- 

 quires more than 600 times its weight of water to effect a 

 solution. It is free from sulphur, and belongs to the group 

 of essential oils characterized by the formula C 5 H 8 , and can 

 become oxidized under contact with the air into valerianic 

 acid (C 5 H 10 2 ), this oxidation being the cause of the pecu- 

 liar cheesy odour of old hops ; it is a mixture of a hydro- 

 carbon C 5 H 3 isomeric with the oils of turpentine and rose- 

 mary, with an oil containing oxygen C 10 H 18 0, having the 

 property of oxidation alluded to. 



Tannic acid is found in the several kinds of hops, in quan- 

 tities varying from two to three per cent., and is an important 

 constituent, as it precipitates the albuminous matter of the 

 barley, and serves to clear the liquor. It gives with the per- 

 salts of iron a green precipitate; treated with acids and 

 synaptase, does not separate into gallic acid and sugar; 

 and by dry distillation, does not give any pyrogallic acid. 

 The hop resin is the important constituent of the hops, and 

 contains the bitter principle or lupuline. It is difficultly 

 soluble in water, especially in pure water, and when the 

 lupuline or essential oil is absent. But water containing 

 tannic acid, gums, and sugar dissolves a considerable quantity 

 of the resin, especially when the essential oil is present. It 

 is intensely bitter in taste, and becomes foliated when exposed 

 to the atmosphere. 



