284 INCUBATION AND BROODING 



Testing the Thermometer. — In starting the hatch, no 

 thermometer, however good the make or however reliable 

 its past history may be, should be used without first test- 

 ing it by comparison with a standardized thermometer. 

 It has been found best to recalibrate or test the ther- 

 mometer at the beginning of each season, as the readings 

 change from year to year. This is due to the "seasoning" 

 of the glass from which the thermometer is made. 



To Test and Recalibrate an Incubator Thermometer. — 

 Provide a large shallow basin of water heated to 110°, 

 place a standardized thermometer and one to be tested 

 side by side in the water with the mercury bulbs about 

 one inch below the surface ; compare the two until water 

 has cooled to 96°, making a note of the comparative read- 

 ing on the two thermometers. Then mark the correction, 

 if any, on the incubator thermometer. 



Effect of Moisture on Incubation. — Close watch needs 

 be kept on the relative humidity of air in the machine. 

 Best results are obtained when the relative humidity is 

 not less than 50 per cent. With most machines the ad- 

 dition of moisture is necessary. The surest and safest 

 way to maintain humidity is by the use of the wet sand 

 tray. The water used for moistening the sand should 

 contain about one per cent of some volatile disinfectant. 

 In order to prevent the lowering of temperature within 

 the incubator, this water should be brought to 102° Fah- 

 renheit before being added to the trays. 



What Constitutes a Good Hatch. — The real test of the 

 hatch is not the fertility but the number of chicks resulting 

 from the total number of eggs incubated. The total num- 

 ber of chicks should not mean the total number that suc- 

 ceeded in freeing themselves from the shells without help, 



