Mar. i8, 1918 



Respiration of Stored Wheat 



693 



kernel, the complex phenomenon being known as respiration. The latter 

 is accelerated by an increase in the rate of diffusion, which in turn is 

 dependent upon the existence of a gel, and the relative viscosity of that 

 gel. For these reasons the moisture content of sound grain determines 

 to a considerable extent the rate of respiration and consequent liability 

 of heating when bulk grain is stored. 



To determine the relation of moisture content to respiration in stored 

 wheat, a large sample of spring-sown Haynes Bluestem wheat known as 

 Minnesota 169 was obtained. The weight per bushel of the sample was 

 57K pounds (26.08 kgm.) ; the w^eight per i ,000 average kernels, 24.62 gm. ; 

 and it contained 2.21 per cent of nitrogen on the dry basis. It was then 

 divided into several portions, and each portion was brought to a different 

 moisture content, the percentages of moisture ranging from 12.50 to 

 17.07 per cent. The quantity of carbon dioxid respired per 24 hours by 

 each 100 gm. of dry matter is given in Table I and is shown graphically 

 in figure i. The rate of increase in respiration is fairly gradual from 

 12.50 to 14.78 per cent, but after the latter percentage is exceeded the 

 rate is markedly accelerated. The break in the curve occurs when the 

 moisture content slightly exceeds 14.5 per cent, and it is probable that 

 this represents about the maximum percentage of moisture that this class 

 of wheat may safely contain without danger of heating when stored in 

 bulk. 



Table I. — Respiration of Haynes Bluestem (Minnesota i6g) -wheat, <^ incubated at j^ -8° C 



for four days 



"Weight per bushel of sample, 57^4 pounds, 

 basis, 2.21 percent. 



Weight per 1,000 kernels, 24.62 gm. Nitrogen on dry 



The acceleration of respiration as the moisture content increases is 

 shown in Table II. These data are based upon the estimated respiration 

 values at even percentages of moisture, and the computed increase in 

 respired carbon dioxid for each increase of i per cent of moisture. In 



computing these data the following formula was employed : —^ — ^^^ 



in which Km represents the respiration value at a particular percentage 

 of moisture, and Km _ i represents the respiration value for the same wheat 

 containing i per cent of moisture less than Km. It is evident that the 

 acceleration between 12 and 14 per cent of moisture is very gradual, while 

 it increases markedly after 14 per cent is exceeded. 



