Licence: In copyright
Credit: Hygiene and public health / by B. Arthur Whitelegge and George Newman. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![Chap, i.] Examination of Air. suspended particles to fall upon the gelatine. Sedg- wick, Frankland, Petri, Pasteur, and others have adopted methods of filtration through sugar, sand, etc., which is subsequently cultured in favourable media. The amount of air examined is measured by a syringe or aspirator of known capacity. Koch relied on exposure of plates of gelatine to the air to be exam- ined. Gordon prefers using broth-plates in the same way, with anaerobic cultivation of the broth at 37 C. for 48 hours with subsequent subculture. Search should be made for streptococci (as indices of saliva), B. coli and JJ. enteritidis sporogenes (as index of recent and non-recent fsecal pollution), and B. viycoides (as index of soil contamination). 2. Organic matter in air may be measured by determining the volume of air required to decolorise a known volume of a standard solution of permanganate of potash, such as 0-395 grm. in 1 litre of distilled water. The air may be aspirated through the solution, or successive volumes washed with the permanganate, by shaking in a bottle, until the solution is no longer pink. Another plan is to aspirate a known large volume of air through distilled water, and then examine the latter by the albuminoid ammonia process, described subsequently. In such estimations it is desirable in each case to make control experiments. Carbonic acid.—1, Pcttenkofer''s method.—The sohi- tions re(iiiire(l are : («) Pure lime-water, saturated ov nearly 80; [b) Standard solution of crystallised oxalic acid of such strength (2-'i5 graiiitnes per litre) that 1 c.c. exactly neutralises 1 mgr. of lime, CaO. From the equation CaO + COo = CaCOa 56 mgr. 41' mgr. 100 mgr. 44 it is evident that 1 mgr. of CaO takes mgr. of COj. The volume of 44 mgr. of CO, at 0-C and 760 mm. pressure, is 44 22*4 c.c, 80 that - - mgr. = 0*4 c.c. Hence, each c.c. of oxalic](https://iiif.wellcomecollection.org/image/b2191218x_0023.jp2/full/800%2C/0/default.jpg)
