Chapter I: Apparatus

1. _Sample Bottles._—Any size, shape or quality of bottle may be used for a bacterial sample, provided it holds a sufficient amount to carry out all the tests required and is such that it may be properly washed and sterilized and will keep the sample uncontaminated until the analysis is made. Four- or eight-ounce, ground-glass-stoppered bottles are recommended. These should be protected by being wrapped in paper, or their necks covered with tin foil, and should be placed in proper boxes for transportation.

2. _Pipettes._—Pipettes may be of any convenient size or shape provided it is found by actual test that they deliver accurately the required amount in the manner in which they are used. The error of calibration shall in no case exceed 2 per cent. Protecting the pipettes with a cotton stopper is recommended.

3. _Dilution Bottles._—Bottles for use in making dilutions should preferably be of tall form, of such capacity as to hold at least twice the volume of water actually used. Close-fitting ground-glass stoppers are preferable, but tight fitting cotton stoppers may be used, provided due care is taken to prevent contamination and to avoid loss of volume through wetting of the stopper before mixing has been accomplished.

4. _Petri Dishes._—Petri dishes ten centimeters in diameter shall be used with glass or porous tops[211] as preferred. The bottoms of the dishes shall be as flat as possible so that the medium shall be of uniform thickness throughout the plate.

5. _Fermentation Tubes._—Any type of fermentation tube[203] may be used provided it holds at least three times as much medium as the amount of water to be tested.