Frost—Bacteriological Control of Public Milk Supplies. 1309 
(E) A Bramhall Deane autoclave. Steam from high pressure 
steam system. 
In the comparative tests the following results were obtained: 
Table b. 
Comparison of Several Different Autoclaves. 
Loss in grams per 100 grams or per cent. 
Autoclave. 
Number of 
bottles. 
Greatest 
loss. 
Smallest 
loss. 
Average. 
A. 
128 
8.8 grams 
0.1 grams 
5.07 grams 
B. 
10 
1.9 
0.9 
1.51 
C... 
10 
3.5 “ 1 
2.7 
3.23 
D. ...1 
10 
8.7 “ | 
6.2 
7.73 
E. 
10 
2.8 
1.8 
2.32 
III. Cause of Loss. 
The loss by evaporation is very evidently due to the fact that 
condensation of the steam filling the sterilizing chamber occurs 
during the process of sterilization. This permits the ebullition 
of the fluids being sterilized. Undoubtedly this goes on during 
the entire process but is perhaps most pronounced at the end 
after the steam has been shut off. When the autoclave is allowed 
to cool off gradually by shutting off the steam a diminished pres¬ 
sure is produced. In autoclave A this varies, as determined by 
experience, from five to fifteen pounds. Under these conditions 
of reduced pressure it would seem that the hot fluid must boil 
with great vigor. If, however, the loss were due solety to the 
boiling at this time, the amount of liquid lost would be independ¬ 
ent of the time of exposure, but this is not in accord with the 
facts observed. It was found that a series of bottles autoclaved 
for five minutes and allowed to cool slowly, lost on the average 
4.8%, while another series run under exactly similar conditions, 
but for an hour and five minutes, and allowed to cool slowly, 
lost 7.6%, or nearly twice as much. 
IV. Prevention of Loss by Use of Closed Autoclave. 
A little reflection convinces one at once that it is possible to 
prevent this ebullition by closing the autoclave while cold and 
keeping it closed until the process of sterilization is completed 
and the autoclave cooled down, thus retaining air. It has been 
