. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . ly adopted because, in addition to holding an amountwhich meets all the requirements of an analysis (eventhough it be necessary to repeat some of the tests), theyare strongly made and of a convenient shape; but ob-viously any stout glass bottle of pretty much the samedimensions, fitted with a glass stopper, will serve thesame end. The bottle must be thoroughly cleansed by first wellrinsing with a little dilute hydrochloric acid,
. Public health laboratory work, including methods employed in bacteriological research, with special reference to the examination of air, water and food contributed . ly adopted because, in addition to holding an amountwhich meets all the requirements of an analysis (eventhough it be necessary to repeat some of the tests), theyare strongly made and of a convenient shape; but ob-viously any stout glass bottle of pretty much the samedimensions, fitted with a glass stopper, will serve thesame end. The bottle must be thoroughly cleansed by first wellrinsing with a little dilute hydrochloric acid, and then • Stout wicker covers are made to protect them in transit whensent by parcel post or rail. 24 LABORATORY WORK. well washing in good water until the washings are nolonger acid. The sample is then thus collected and dealt with :—The bottle is first quite filled with the water and thenemptied ; the sample is taken, and the glass stopper,having been found to fit accurately and tightly, is tieddown firmly on to the neck of the bottle, and the knotsare protected with sealing wax. A label having beenattached, care is taken to keep the sample cool and un-. FiG. 23.—The Winchester quart bottle with label affixed. exposed to light until the analysis is commenced, andunder no circumstances should the major part of theanalysis be delayed more than 48 hours, or importantchemical changes may transpire. Although information is often furnished, and gene-rally demanded, on all the points bearing upon thepossibilities of pollution which the water has incurred,it is often best not to avail oneself of the information COLLECTION OF SAMPLES. 25 until the analysis is completed, otherwise there is a strongincentive to treat cursorily some part of the analysis,on the supposition that it is unnecessary, which withdue care, might have disclosed an undreamt of sourceof pollution. Regarding such information, the mostimportant to the analyst would be that bearing uponthe constitution of the
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