230 



STATE BOARD OF AGRICULTURE 



venieuce sake may be dispensed with when no degree of accuracy 'is 



demanded as in experimental work. 

 Autociav. Mention has been made 



of the use of steam under 

 pressure and of course at a hi^dier 

 degree. For this method of steri- 

 lization, a special sterilizer is neces- 

 sary and is called an autociav. This 

 is of much the same pattern as the 

 steam sterilizer just described, but 

 instead of the steam escaping, the 

 chamber is made steam tight so as 

 to withstand several pounds pressure. 

 At the top is a gauge to denote the 

 pressure and a safety valve to pro- 

 vide against danger. The thermo- 

 meter is present as in the other 

 case. In this apparatus, the steam 

 may be raised to 115° C. [239° F.] 

 or 130° C. [266° F.] and one con- 

 tinuous heating will be equivalent 

 to several discontinuous heatings in 



the ordinary steam sterilizer, thus Fig. 13, Autociav. 



saving much time. The activity of steam becomes far greater as the tem- 

 perature passes above 100° C, [212° F.]. Owing to the saving of time 

 from the greater activity of the steam at 130° C. [266*" F.], this apparatus is 

 much favored in some places for certain purposes. 



Moist heat is adapted to the sterilization of media or liquids which ar© 

 prone to evaporate or undergo decomposition in the process of heating. 

 The preserving of fruits and vegetables may be accomplished by this 

 means and in canneries this agent is utilized in some manner. Anything 

 that will stand boiling or steaming may be subjected to this method of 

 sterilization without detriment and may be thoroughly sterilized if the 

 boiling water or steam will penetrate the material. 



I hesitate to consider the time required because it depends upon a great 

 variety of conditions and it is impossible to include them all. Some time 

 is always required to raise the substance under process of sterilization to 

 the ^me temperature as steam. If there is a large bulk, much time is 

 required; if only a small bulk, a few minutes will do. With this in mind, 

 it may be safe to state that two or three minutes will kill all bacteria in 

 the vegetative form. As an illustration of this, liquid in a tube three- 

 fourths of an inch in diameter may be sterilized at 100° C. [212° F.] for 

 fifteen minutes each day during three successive days — the fractional or 

 discontinuous method. Heating once at 130° C. [266° F.] in the autociav 

 will accomplish the same thing. If this same liquid were placed in a can 

 holding a quart, that quart of liquid would require at least an hour's 

 heating each day for three successive days. The situation is now stated, 

 and the conclusion can only be an exercise of the judgment in ascertain- 

 ing how long it will take to raise the substance to the degree required. In 



this way sterilization by moist heat is conductftl. 

 Dry heat. ^g ^^g guggested at the beginning of this discussion on 



sterilization, each form has its advantages over the others. 



