CH. Ill] VESSELS, ETC., USED IN CULTIVATIONS 39 



in the air-chamber for several hours (three to six) to a te m- 

 perature of from 130° to 150° C. . while hot they are taken 

 out seriatim, plugged with the sterile cotton-wool, and re- 

 placed in the air-chamber, and heated again for several 

 hours. All this, and other operations to be described below, 



'l 



KjG. 4.— Hot Air-chamber for Sterilising Test-tubes, Cotton-wool, &c. 



An iron chamber with double wall, the inner chamber having separate folding 

 doors. In the inner chamber are placed the test-tubes, glasses, &c., and the 

 cotton-wool, the latter in a loose condition. Both sets of doors are closed; and 

 the apparatus heated by a large Fletcher's burner. A thermometer passing from 

 the inner chamber through the upper wall indicates the temperature of the chamber. 

 The hot-air apparatus can, according to the requirements of the laboratory, be 

 constructed of larger size than the one here depicted. I use one that is made four or 

 five times this size and is divided into several compartments. 



may appear to some rather tedious 'and unnecessarily com- 

 plicated, but it cannot be too strongly insisted on that in 

 these matters one cannot be too scrupulous. A slight re- 

 laxation may, and occasionally is, followed by disastrous 

 consequences in the shape of accidental contamination, and 

 consequent loss of materials prepared at the cost of much 



