. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . d the use of thefollowing apparatus:— The Autoclave.—This is a form of Papins is represented in figure 100, and consists of a boiler towhich may be firmly fixed a lid furnished with a steamcock, safety valve and gauge ; the latter indicates thesteam pressure and the temperature corresponding to it,thus a pressure of one atmosphere of steam correspondsto a temperature of 120° C. It is the most generally serviceable of
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . d the use of thefollowing apparatus:— The Autoclave.—This is a form of Papins is represented in figure 100, and consists of a boiler towhich may be firmly fixed a lid furnished with a steamcock, safety valve and gauge ; the latter indicates thesteam pressure and the temperature corresponding to it,thus a pressure of one atmosphere of steam correspondsto a temperature of 120° C. It is the most generally serviceable of all the steril-isers, both on account of the rapidity of its action, andfrom the fact that a short exposure in the super-heatedsteam serves to thoroughly sterilise. In its use certain precautions must be adopted. Caremust be taken that there is sufficient water in the 430 LABORATORY WORK. bottom reservoir, and that all the air is thoroughlydriven out before the steam cock is shut off. If thelatter precaution is not taken the gauge will record, inaddition, the pressure of the expanded air; thereforeto ensure that all the air is driven out, the steam should. Fig. ioo.—The autoclave, showing flasks in the interior undergoing sterilisation. be allowed to issue through the stop cock for about fiveminutes. When the cock is closed, the guage must beclosely watched, lest any accident should happen. Thedesired temperature having been reached, the gas mustbe lowered, in order to keep the temperature con- STERILISATION. 431 stant. The stop cock nrnst not he opened till the pressure in-side the boiler has regained the normal. For most purposes an exposure to a temperature of115° C. for twenty minutes, or to 120° for ten to fifteenminutes, serves to sterilise. Gelatine, it is to be re-membered, must not be superheated, so that the stopcock must be left open whilst making it. In the manu-facture of agar, the autoclave is very useful, the high
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