Mar. 8, 1924 
Effect of Nitrate on Prussic Acid in Sorghum 
719 
this seeding were all used in perfecting the manipulative procedure, and 
for these there are no quantitative data. Qualitative tests showed that 
those plants grown with added nitrate contained a higher proportion of 
hydrocyanic acid. 
method of analysis 
The method of analysis thus developed and used with the subsequent 
plantings was as follows : 
The fresh green material was weighed, passed through a food chopper, 
and placed in a Kjeldahl flask, with not more than 500 cc. of water, using 
only enough to wash the sorghum out of the chopper into the flask. This 
mixture was allowed to autolyze for two hours at 45 0 C., or over night at 
room temperature, and then, without addition of acid, distilled into 
dilute sodium hydroxid solution. The basic distillate was then treated 
with 2 or 3 cc. of a 3 per cent solution of ferrous sulphate, and allowed to 
stand about 20 minutes, by which time part but not all of the iron was 
oxidized to the ferric state, and then made acid with dilute sulphuric 
acid. The blue color developed slowly or quickly, according to the 
amount of hydrocyanic acid present, and on this account it was found 
best for the test solution to stand for some hours before being compared 
in a Campbell-Hurley colorimeter with the standard color prepared 
from potassium cyanid. 
It was found convenient to make the standard equivalent to 10 
mgm. of potassium cyanid per 100 cc. of standard solution, and usually 
about 30 gm. of the green sorghum was used for each determination, 
but in the case of green leaves, or of very young whole plants, much 
smaller samples sufficed, while with large, stocky plants, larger samples 
were necessary. As about 150 cc. of distillate was usually secured, the 
volume of the test solution was made up to 200 cc. except in cases of 
samples that contained unusually large amounts of hydrocyanic acid, 
when the volume was increased. 
SORGHUM FROM LATER PLANTINGS 
As soon as the first crop had been harvested, seed was planted among 
the roots, on January 30, and the second crop grown without cultivation 
or addition of any fertilizer except nitrate. 
The plants of the second crop on the Thurston loam subsoil, where no 
nitrate had been added, were short, slender, and very light in color, 
indicating extreme nitrogen hunger, and did not furnish enough hydro¬ 
cyanic acid to permit of its quantitative determination, or in some 
cases even to permit of its detection (Table I). Even the lighter applica¬ 
tions of nitrate produced marked improvement in growth and color, 
and gave readily measurable amounts of hydrocyanic acid. Larger 
applications of nitrate raised the hydrocyanic-acid content proportion- 
ately. 
The nitrogen hunger was not marked in the first crop on the Merrimac 
loamy sand, and even in the second crop it was not extreme. Although 
the available nitrogen in the unfertilized jars had been diminished by the 
first crop, there still remained enough to give a growth to the plants of 
the second crop better than on either of the other soils. In the case of 
lots E and F, there was no difference in appearance between the plants 
grown with and without nitrate, but in lot I the plants without nitrate 
were much lighter in color. In every lot the percentage of hydrocyanic 
acid was considerably increased by the addition of nitrate (Table II). 
