Disinfection and the preservation of food : together with an account of the chemical substances used as antiseptics and preservatives / By Samuel Rideal.

  • Rideal, Samuel, 1863-1929.
Date:
1903
Catalogue details

Licence: In copyright

Credit: Disinfection and the preservation of food : together with an account of the chemical substances used as antiseptics and preservatives / By Samuel Rideal. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

    49/532 (page 33)
    35 and badly conducting articles much more rapidly than dry heat. In entering the interstices of cold bodies steam undergoes condensation and imparts its latent heat to the objects in contact with it. At the same time, as water, it occupies only about rirVr of its former volume. To fill the vacuum thus formed more steam enters, and so on until the whole mass has been penetrated. On the other hand the contraction of hot air in cooling is very much smaller; being, for each i° C, ?vi! of its volume at o. As an example, 394. volumes at 121° C. would become 283 volumes at 10°, a contraction of only about 28 per cent. The work of Pasteur, Tyndall, Lister, Koch, Parsons, and others, has, therefore, determined the fundamental conditions for successful disinfection by heat. Conditions required in a Disinfector It remains to- be shown that the mechanic can meet the requirements of the bacteriologists, and, at the same time, deal with the practical difficulties that invariably arise during the intro- duction of novel machinery. The conditions for dry-heat disinfection, so far as temperature and duration of exposure are concerned, have not been very clearly defined; but from experience gained by Dr. Hopwood at the London Fever Hospital, it may be gathered that an exposure of bedding to hot air at a temperature of 121° C. for a period of nine hours is generally sufficient, and no material damage is caused thereby to the goods. The great difficulty in designing a stove to fulfil these conditions arises from the fact that it is almost impossible to obtain a uniform equable temperature in a sufficiently large chamber. Exposure to air at a temperature of 127°' C. for nine hours weakens many woollen materials, and a temperature of 138° C. distinctly discolours them, whereas an error of five or ten degrees on the lower side of 121° C. renders disinfection by these means uncertain. The allow- able range of temperature in a hot-air disinfector should, therefore, not exceed 10°, and the mean should be about 121° C, since, according to Drs. Parsons and Klein, the free exposure of anthrax spores to air at 118° C. for one hour suffices for their destruction. Most engineers are well acquainted with the great difficulty met with in heating air to a uniform temperature, D