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a large flask. Before filtering the broth, the filter paper 

 must be filled with water to see that there are no holes in 

 it; the solid particles are then pressed with an ordinary 

 meat press, the fluid squeezed out, and added to the filter. 

 The filtered broth is made slightly alkaline by gradually 

 adding a few drops of potassium hydrate, stirred, and tested 

 with a piece of turmeric paper. When slightly alkaline a 

 cotton wool plug is put in the flask, and it is put inside 

 an autoclave, where the heat generated is 115 to 120 C. 

 There is no thermometer attached to indicate the heat, but 

 the machine is so constructed that, whenever the pressure 

 of the steam inside raises the temperature beyond 120 C., 

 a safety valve allows some steam to escape. The manometre 

 indicates the pressure, but the machine is self-adjusting. 

 If the liquid in the flask is half a litre, five minutes of 

 steaming is quite enough ; if five litres, 20 minutes is 

 necessary to clarify the broth. The lid of the autoclave is 

 fastened with hooks to retain the pressure of the steam. 



1,361. When the five minutes (or 20 minutes, as the case 

 may be) are over, the gas is to be turned out, and the steam 

 allowed to escape very gradually. When cool, the lid is to be 

 opened and the flask taken out. The broth is now clarified, 

 and the precipitate will have to be removed by filtering again. 

 The filtering is done into flasks with very long necks, and 

 when about three-fourths full, the flasks are sealed at the lower 

 part with a blowpipe flame by continual turning, and the long 

 neck is broken off and thrown away. The sealed flasks 

 are then put inside the autoclave again at 115 or 120 C. 

 for 15 minutes to sterilize the contents, that is, to kill any 

 organic germs. When out of the autoclave, the flasks of 

 broth can be kept in store for any length of time, and for 

 use, the sealed neck will have to be rasped and cracked 

 open, and the broth transferred with the help of a ballon 

 pipette into matras. Lest any organism should settle in 

 these operations, the matras are left for 8 to 15 days on the 

 VVVV 



