Atmospheric carbonic acid, its estimation and variaton / lecture delivered by John Robertson on Wednesday, June 8th, 1904.

  • Robertson, John.
Date:
1904
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Licence: In copyright

Credit: Atmospheric carbonic acid, its estimation and variaton / lecture delivered by John Robertson on Wednesday, June 8th, 1904. 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.

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    This appears to be very simple and easy of application, but in practice great care is reqiiired to ensure tbat tbe air under examination is kept at exactly tlie same temperature and pressure and tbat tbe wliole of the apparatus is in good working order. My own personal experience with the apparatus has not been very great though I have used it at intervals during the past three years. I have had some obviously inaccurate results when I least expected them, and it is the fear of a repetition of these results which makes me stick to one of the older methods which, though much more tedious, is, I think, more under control. Demonstration of Haldane's apparatus was given here. There are on the market many other varieties of apparatus for estimating the amount of atmospheric C0„. Most of these have some defect rendering them inaccurate or else they are mere modilications of the Dalton process. Corrections for Temperature and Pressure. A point which will arise in these determinations is as to whether it is necessary to correct for temperature and pressure. For all work where scientific accuracy is required such corrections must be made. On the other hand in estimations made with a view to ascertaining the amount of CO2 for the purpose of judging of the sufficiency or otherwise of the means of ventilation correction to normal temperature and pressure is unnecessary as the temperature and pressure at which the samples are analysed are relatively uniform and therefore the results are fairly comparable. Personal Error. A much more important point is to know accurately the amount of one's own experimental error. This will vary for each observer. If a uniform amount of care is observed the amount of the error will be consistently imiform. My own error with the Dalton method is 0'24 volume of COo per 10,000 volumes of air, i.e., if I find 324 volumes of CO2 in air I know I am dealing with air containing three volumes only; if 20'74 the corrected figure would be 20'5. It is most important to test one's results against such a gravimetric method as that of Haldane and Pembrey or that of Professor Letts and Mr. Blake. The effect of experimental error is indicated by the statements in most of our text-books that pure air contains about four volumes per 10,000, when, as a fact, such air contains rather less than three volumes—an error of about 33 per cent, when pure air is being dealt with, or of 7 per cent, when air containing ]4 volumes of COg per 10,000.