Reports of the special Committee upon Pathological Methods. V, The reaction of media.

  • Great Britain. Medical Research Committee. Special Committee upon Pathological Methods.
Date:
1919
Catalogue details

Licence: Public Domain Mark

Credit: Reports of the special Committee upon Pathological Methods. V, The reaction of media. Source: Wellcome Collection.

    11/20 (page 9)
    The method of employing phosphate solutions of a definite hydrogen 10n concentration and phenol red as an indicator, as standards for bacteriological work, was introduced by Hurwitz, Meyer, and Ostenberg on the basis of the previous work of Levy, Rowntree, and Marriott, who had determined the reserve alkali of the blood in this way. Hurwitz and his co-workers compensated for the colour of the medium by placing tubes of media in a line with the standard solution. In this way a very perfect compensation is easily accomplished. It is the same method which Walpole had previously employed in a different way. The standard solutions of Hurwitz, Meyer, and Ostenberg have been since employed by. Cole and Onslow and by Clark. Cole and Onslow use two standard solutions instead of one, and Clark has developed media based on the reaction between potassium phthalate and acid potassium phosphate and hydro- chloric acid or sodium hydroxide. With these reagents standard hydrogen ion solutions may be prepared ranging from Py = 2-11 to Py = 8-02. The solutions necessary for preparing a set of standards of definite hydrogen ion concentration are: 1, A 1/15 molecular solution of acid potassium phosphate EEL 2O,. 2, A 1/15 molecular solution of disodium phosphate Na,HPO, 2 0). 3. A 0-02 per cent. solution of phenol red. The following are the directions for preparing these solu- tions : 1. A pure acid potassium phosphate is prepared by recrystalizing the salt two or three times from distilled water. It is dried first between filter paper and finally in a water oven at 100°C. Of this salt, 9-078 grams are weighed out and dissolved in about 500 c.c. of distilled water contained in a litre flask; 45-5 ac. of the indicator solution are added and the volume made up to 1,000 c.c. with distilled water. 2. The dihydrate of disodium phosphate has been found to be the most suitable for preparing a standard solution. It is made as follows: A quantity of the crystalline sodium phosphate of the pharmacopoeia, which should be of the purest quality, is placed in a flat dish in a layer not more than 1-2 cm.deep. It is covered with paper to protect from dust and allowed to stand for about two weeks at room temperature. The room should be dry; for when the atmosphere is very humid, the salt may not lose the necessary quantity of water. The salt should be turned over with a spatula every second day, and any of the larger lumps crushed. At the end of two weeks the salt is trans- formed into a snow-white granular substance having the com- position Na,HPO,, 2 H,O. A check may be made of the loss of weight during the last tew days by weighing out about a hundred grams with an accuracy of 0-1] gram and weighing again in the course of a couple of days. The two weights should agree to 0-1 gram. It is advisable to have the water content of the salt