Abstract
Because of the interest aroused by a device made in this laboratory for the automatic drawing of samples from flowing gas, a brief description is being presented. The apparatus is in use here in conjunction with open-circuit respiratory metabolism determinations, the analyses for CO2 and O2 being performed on a Carpenter-Haldane analyzer, 1 but it can obviously be of service in any situation when it is desired to draw a continuous sample of gas over a set period of time.
Benedict and Ritzman 2 have described a method of drawing gas samples by attaching a Lee pump 3 to gearing activated by electromagnets controlled from the gas meter. The present apparatus uses a larger pump of similar construction but with the stopcock built into the cylinder head. The driving power is transmitted by gears to the threaded shaft from an electric motor which runs the blower. The sampler has the following qualifications:
Continuom drawing of a predetermined volume is obtained over a sect length of time, not dependent upon the rate of gas flow. Since a single electric motor drives both the blower and the sampler through separate gearing, variations in gas flow due to fluctuations in electric current will automatically be compensated for in the aliquot drawn. The separate gearing allows the operator to vary the collection time of samples and the velocity of air passage independently of each other but insures a constant aliquot at all times.
Careful construction renders the sampler sufficiently gas tight so that a sample can be left in the apparatus (with the stopcock closed) for more than 12 hours with perfect safety.
Accurate estimation of the volunie of samples can be obtained directly from the length of exposed pump shaft.
In all, a rugged system has been evolved, capable of functioning continuously over long periods of time without requiring constant adjustment and attention.
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