and Laboratory Methods. 



1973 



The incubator (Fig. 1) is a wooden box '22.5 x 20 x 27 inches, made by a local 

 carpenter, and consists of two layers of seven-eighths boards (B and C) with an 

 inch space between them (D), which is lined with building paper and filled with 

 sawdust. Externally the box is covered with a layer of paper over which is a 

 layer of three-eighths matched boards (E). The inside is lined with zinc. The 

 box is supported by extensions of the sides and back, which raises the bottom 

 eight inches from the floor, leaving a space for a drip pan. The door (A), made 

 of two thicknesses of wood with paper between, is at the top. Below this is a 

 removable galvanized iron frame carrying a sheet of plate glass (K). The 

 chamber is divided into two parts by a movable partition (L) of galvanized wire 

 gauze. Around the walls of the upper chamber and entirely covering them is 

 coiled a quarter-inch thin walled lead pipe (G) having inlet and outlet at (M) 

 which carries water for cooling purposes. 



Heat is supplied when necessary by a 16 candle lamp, the bulb of which is 

 blackened. This lamp (H) is situated in the lower chamber and at a consider- 

 able distance from the regulator. The lamp is turned on or off as required by 



Fig. 2. 



a contact maker (Fig. 2) controlled by the regulator (E). The contact maker is 

 a modified telegraph sounder, the arm of which has been lengthened in order to 

 obtain the motion necessary to snap out the arc formed on breaking the circuit. 

 Current for the contact maker is supplied by a battery of four gravity cells in 

 series. The regulator (F) is constructed to close the circuit when the tempera- 

 ture falls below a predetermined point. It contains mercury in the arm and lower 

 small bulb, the other bulbs containing air only. Contact is made through the 

 mercury, one terminal being immersed in the mercury in the lower bulb, the 

 other sealed into the arm. The regulator is adjusted by letting air into or out 

 of the large bulb through the stopcock. This stopcock should be selected with 

 special care, as it must be absolutely gas tight. 



The working of the apparatus is as follows : 



Water from the city supply is allowed to flow continuously through the lead 

 coil. When the temperature falls below the point at which the regulator is 

 adjusted, contact is made in the regulator closing the circuit through the lamp, 

 which stays lit until the temperature rises to the required point. When water 

 can be obtained directly from the street main it is usually cool enough. If its 

 temperature becomes too high to properly cool the chamber, the water is cut off 

 entirely and a piece of ice placed in the lower compartment. 

 Hoagland Laboratory. E. H. WiLSON. 



R. B. Fitz-Randolph, 



