6 BULLETIN 1013, U. S. DEPARTMENT OF AGRICULTURE. 



products. The shaded portion marked " invisible loss " is the differ- 

 ence in the weight of the wheat with the temper water added and the 

 total weight of mill products obtained from milling. With each 

 increase of relative humidity there is an appreciable decrease in the 

 invisible loss occurring during milling and a proportionate increase 

 in the total yield of mill products. For example, the average in- 

 visible loss resulting from milling 11 samples at relative humidities 

 ranging from 25 to 29 per cent, inclusive, was 5.2 per cent, while in 

 milling 59 samples at relative humidities ranging from 65 to 69 per 

 cent, the average invisible loss amounted to only 3.3 per cent. This 

 loss in weight is due principally to the evaporation of moisture con- 

 tained in the wheat, and, except in the cases of low atmospheric 

 humidity, amounted to less than the quantity of water added in tem- 

 pering. In other words, the weight lost through the evaporation of 

 moisture during milling was greater than the weight of the temper 

 water added when the samples were milled at relative humidities 

 lower than 35 to 39 per cent and less when milled at higher relative 

 humidities. 



COMPARISON OF THE INFLUENCE OF RELATIVE HUMIDITY AND 

 OF MOISTURE CONTENT OF WHEAT ON MILLING YIELDS. . 



That both the relative humidity of the air and the moisture content 

 of the untempered wheat have a considerable influence on the weight 

 lost or gained during milling as compared with the weight of the 

 wheat before tempering is quite evident from figure 3. In preparing 

 this diagram the samples were grouped according to certain ranges 

 in the percentages of moisture contained in the wheat samples before 

 tempering, and a separate curve was made for each group. This 

 scheme of diagramming makes it possible to show the relation of 

 both relative humidity and moisture content to the total yield of 

 mill products. 



The curves show that the higher yields are associated with the 

 higher relative humidities and with the wheats of lower moisture 

 content. Each 10 per cent increase in relative humidity above 35 

 per cent shows an average increase of about one-half of 1 per cent in 

 the total weight of the products obtained, and each decrease of 1 per 

 cent in the moisture content of the wheat before tempering shows 

 about six-tenths of 1 per cent increase in yield. Compared with the 

 weight of the wheat before tempering, the samples containing from 

 9 to 9.9 per cent moisture showed a net gain in weight of total mill 

 products for all relative humidities given, while the samples contain- 

 ing from 12 to 12.9 per cent moisture before tempering showed a net 

 loss in weight of total mill products except for relative humidities 

 higher than 60 to 69 per cent. The greatest average gain in weight 



