Fig. 124. Curve of the temperature of the water contained in the steriliser, and of the bottles immersed in it.
M. Chavane demonstrated in my laboratory at the Charité that milk immersed in boiling water for forty-five minutes attained the temperature of the water -- 100° C. His results, however, have been disputed. Marfan [1] writes:
"What is the actual temperature of the milk contained in the small bottles when surrounded by the boiling water of the steriliser for forty-five minutes? Some say that it does not exceed 80° C.; Chavane alleges that it reaches 100° C.; so I re-investigated the question. During various phases of the sterilisation I placed a thermometer, graduated to 200° C., in the small bottles. After a quarter of an hour the temperature of the milk is between 90° and 92° C.; after half-an-hour, between 95° and 96° C. As I never found it surpass the last figure, the casein ferment is probably not destroyed by this process. The efficiency of the sterilisation varies with the duration of the heat: according to Freer, after fifteen minutes heating several hundreds of colonies develop within twenty-four hours; after thirty minutes, several dozens, and after forty-five minutes sterile plates are often obtained. Rodet corroborates these results."
I asked M. Nicloux to repeat M. Chavane's experiment. He did so, avoiding all possible sources of error with the greatest care. His results show that the milk quite readily attains a temperature in the neighborhood of 100° C., viz. 99.9° C. One cannot conceive how it could be otherwise. He used a specially constructed thermometer of great precision, graduated in fifths of a degree to 200° C. Variations of 1/16 of a degree could be readily appreciated by it. The experiments were carried out with the same apparatus as is daily used to sterilise milk in the Clinique. M. Nicloux says:
"I placed one thermometer in the water of the steriliser, and another in one of the small bottles containing the milk which was being sterilised. As I could not then put on the lid, I used a folded towel to prevent the steam escaping too freely. Temperature readings were taken every five minutes, as is seen in the first curve (the abscissa represents time; the ordinate, degrees Centigrade). The dotted line marks the beginning of boiling; the temperature at boiling-point was 96° C. in the steriliser, and 77° C. in the small bottles. After this point was reached, readings were taken every two and a half minutes. Ten minutes later the temperature was found to be 100° C. in the steriliser and 99° C. in the small bottles. On multiplying the ordinate by 20 (Curve 2) one finds, that while the temperature of the water remains constant at 100° C., that of the milk in the small bottles rises till it attains 99.9° C., but no further."
[1] Marfan, Traite de l'allaitement et de l'alimentation des enfants, Paris, 1899.
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Fig. 124. Curve of the temperature of the water contained in the steriliser, and of the bottles immersed in it. |