METHODS OF HATCHING CHICKENS 313 



These instruments, however, do not give the actual relative 

 humidity in the machine. To get a reading of the hygro- 

 meter that will represent the humidity of the whole egg 

 chamber, it is necessary that the bulb be fanned. That is 

 because the moisture which is evaporated from the bulb 

 remains near the bulb, and that part of the egg chamber is 

 therefore more moist than other parts of the machine. 



By fanning the bulb, if that were possible in the in- 

 cubator, the stagnant moisture in the machine would be 

 driven from near the bulb, and the reading would then 

 represent actual conditions of the whole egg chamber. It 

 is in this way that the Government weather bureau obser- 

 vations of the humidity of the air are secured ; the hygro- 

 meter is fanned. It is not practicable to do this in the 

 incubator, nor is it necessary in practice to know the cor- 

 rect humidity. It is sufficient to know that a certain read- 

 ing of the wet bulb thermometer, or a certain percentage 

 of humidity as determined without fanning gives the 

 desired condition for successful hatching. 



Loss in Weight of Eggs a Guide to Moisture. Another 

 method of learning whether the humidity is right is to 

 weigh at intervals of a few days during the hatch a number 

 of eggs and note the loss in weight. A dozen eggs may be 

 marked and weighed when put in the machine, then again 

 every six days until the 18th day. An accurate scale of 

 course must be used. Different eggs vary in the amount 

 of loss due to the difference in the texture or structure of 

 the shell, but an average loss within the following limits 

 has been found to be about right : 



During the first 6 days 3.5 to 4 % loss 



During the second 6 days 4 to 4.5% loss 



During the third 6 days 4.5 to 5 % loss 



Total 12. to 13.5% loss 



(Utah Bulletins 92 and 102. Oregon Bulletin 100.) 



