AGEICULTUKAL CHEMISTRY — ^AGROTECHNY. 507 



the maximum amount of hydrocyanic acid (0.045 per cent) was found in the 

 24-in. plants." 



Solvents employed in the determination of hop-bitter constituents and 

 their estimation by means of cold extraction, R. Seibriger ( Wchnschr. Brau., 

 SO {1913), Nos. 12, pp. 111-119; 13, pp. 196-198, fig. 1; abs. in Chem. Abs., 1 

 {1913), No. 19, p. 3381).— The author states that by constantly shaking hops 

 with cold petroleum ether (boiling point 30 to 50° C), the bitter principle can 

 be removed in from three to four hours. This can also be accomplished by 

 shaking with carbon tetrachlorid in the cold for from one to two hours, but the 

 results are higher. Boiling petroleum ether gives intermediate results. 



Investigation on hops. — IV, A method for quantitative determination of 

 resins in hops, O. Winge and J. P. H. Jensen (Compt. Rend. Lab. Carlsberg, 

 11 {1914), No. 2, pp. II6-I4I).— It is pointed out that the valuation of hops for 

 brewing purposes must be made on the basis of the chemical analysis, and the 

 object of this work was to find a convenient method whereby hops could be 

 valued by chemical means without the services of a skilled operator. It is be- 

 lieved that an approximately correct expression of the value of hops can be 

 obtained by the following cold extraction method : 



Thirty gm. of hops is comminuted by passing through a meat chopping ma- 

 chine. The first 5 gm. coming through the machine is discarded and the re- 

 mainder coming through, which is usually about 15 gm., is carefully mixed. 

 Five gm. of this, corresponding to a volume of 25 cc, is removed with a measur- 

 ing glass and placed in a 300-cc. Erlenmeyer fiask of known weight. The flask, 

 with its contents, is weighed, dried in a vacuum desiccator for 24 hours at 35° 

 C. over sulphuric acid, and again weighed, the loss in weight representing the 

 moisture content of the hops. Then 150 cc. of water-free ethyl ether is added, 

 the mixture allowed to stand for about one-half hour, with repeated shakings, 

 the ether extract is filtered into an Erlenmeyer flask, and the residue and 

 filter washed with 100 cc. of ethyl ether. The ether extract is then titrated 

 with twentieth-normal potassium hydroxid solution in 93 per cent alcohol, 

 using from 6 to 8 drops of a 1 per cent phenolphthalein in 93 per cent alcohol 

 as the indicator, until a permanent red tint is obtained. Since 1 cc. of the nor- 

 mal potassium hydroxid solution corresponds to 0.4 per cent of resin, the per- 

 centage of resin in water-free hops is equal to this factor multiplied by the 

 number of cubic centimeters of potassium hj'droxid solution utilized, divided by 

 the total solids of the hops. 



A method for the recovery of the ether used is described. 



The resin of hops, contrary to previous opinion, is considered of value, be- 

 cause it gives flavor to the wort and aids in the precipitation of the proteins. 

 "Although the resins of hops, which are all soluble in cold ethyl ether, are not 

 all equally bitter and equally valuable — the relation between their bitterness 

 can be expressed by the proportion o : /3 : 7=10 : 7 : 4 — yet the total quantity 

 of resins extracted from the hops by means of cold ether and determined by 

 titration is an approximately accurate expression of the bitterness value of 

 hops." 



A comparative study was made between the cold ethyl ether extracts made 

 and the carbon tetrachlorid method of Seibriger. See also work by Tartar and 

 Bradley previously noted (E. S. R., 27, p. 814). 



Investigations on hops. — VII, The employment of artificial light in titra- 

 tion of the resins in hops, S. H. Labsen {Compt. Rend. Lab. Carlsberg, 11 

 {1915), No. Jf, pp. 184-181, figs. 2). — In the course of work on the quantitative 

 determination of resins in hops by the Winge and Jensen method, noted above, 

 it was found that on dark or cloudy days difficulty was experienced in noting 

 the end point during the titration process. A titration table was devised to 



