80 



atoms from that hitherto accepted ; whilst, from its chemical nature, 

 he is of opinion that it contains a lactone group and belongs to the 

 class of pseudo-acids. These lactones, in aqueous or alcoholic 

 solution, can be titrated by alkalies, exactly as can the acids, except 

 that the reaction is slower. This peculiarity of the a-acid would 

 account for the author having obtained equivalent weights of 345 and 



"^^ 



337 by titration with alcoholic potash, agreeing well with the 



theoretical value of 352. The fact that this titration is possible 

 proves that in neutralisation there is no further breaking down of the 

 molecule but only a " rearrangement " ; otherwise values varying 

 largely from the theoretical would have been obtained. 



Therefore, according to SCHNELL the a-acid is most probably a 

 lactone functioning as a pseudo-acid, and the name " a-acid " might 

 be replaced by " Humulone," and, correspondingly, the unsaturated 

 oxyketonic acid formed on splitting up this " humulone " should be 

 described as " humulinic acid." 



Following upon these preliminary remarks concerning the 

 general chemical properties of the bitter resin and the crystalline 

 bitter principles present in hops, it remains to consider the distribution 

 of these bodies in the hop-flour, and their bearing in practical 

 brewing. 



Lupulin must be regarded as the actual source of the bitter 

 principles of hops. 



Lupulin, or hop-flour, consists of small organised granules or 

 lupulin grains. They form a part of the gland formation of the hop 

 cone, and HoLZNER 1 distinguishes 



1. Isolated glands. 



2. Head glands. 



3. Glandular scales. 

 The last form hop-flour or lupulin granules. 



Under the microscope they appear like multicellular, shield- 

 shaped scales, with conical or cup-shaped indentations, and 



1 Zeitschriftj. d. ges. Brauwesen, 1877, 267 ; 1892, 337 ; 1893, 103 ; 1899,87. 



