126 Journal of Agricultural Research voi. xxii. no. 3 



obtaining a uniform blue color. Very often the precipitate was decidedly 

 green. It was found that by warming and letting the precipitate 

 stand for some time in loosely stoppered bottles a uniform blue color 

 could be obtained. The use of nitric or sulphuric acid instead of hydro- 

 chloric acid or the addition of potassium fluorid, all of which have been 

 suggested by other workers, did not seem to eliminate, entirely, the 

 green color. While the defects of the Prussian-blue method are fully 

 realized, it compares favorably with other methods.' In no sense are 

 the values reported in this paper to be regarded with the same degree of 

 accuracy as a protein or even a crude-fiber determination. For this 

 reason no conclusions should be drawn from the results unless the figures 

 presented are uniformly consistent or the differences large. 



The calculations in this paper are based upon approximately 200 gm. 

 of green material. When the grass was wilted or dry the weight of sample 

 used was proportionately lessened. It is impracticable to secure green 

 samples of uniform weights of dry matter, particularly if they are 

 gathered during different hours of the day and throughout several weeks 

 and months. Then, as will be shown in what follows, the hydrocyanic 

 acid is localized in the plant, being present in the largest amounts in 

 those portions of the plant possessing the greatest vegetative activity. 

 For this reason leaves were separated from the stems whenever these 

 were present. The amount of hydrocyanic acid obtained is small in 

 proportion to the total weight of samples used. It was seldom more 



than 0.015 per cent. 



EFFECTS OF MACERATION 



The first sample was collected June 22, when the grass was about 6 

 inches high. This was cut into pieces about % inch long and digested for 

 three hours in water at room temperature. Less than i mgm. hydrocy- 

 anic acid was obtained. Another sample, taken the next day, was cut 

 and thoroughly macerated by pounding in an iron mortar and was then 

 digested in water. This sample gave 27 mgm. hydrocyanic acid. On 

 June 28 a sample was secured and divided into two equal portions. One 

 portion was cut and macerated as described above, and the other was 

 cut and macerated with coarse, sharp sand. Both were digested in 

 water for the same length of time. The portion macerated with sand 

 gave 26 mgm. hydrocyanic acid, and the other gave 36 mgm. It ap- 

 peared from this that maceration with sand was not necessary and might 

 result in a loss. Subsequent experiments showed that as soon as the 

 grass is macerated the hydrocyanic acid is liberated and for this reason 

 may be lost. On August 18 a sample was divided into four portions 

 and, after the preliminary treatment mentioned, was digested overnight, 

 with the result given in Table I. 



* ViEHOVER, Arno, and Johns, Carl O. on the determination of small quantities op hydrocy- 

 anic ACID. In Jour. Amer. Chem. Soc, v. 37, no. 3, p. 601-607. 1915. 



