Microanalysis of fractions of a cubic millimeter of gas.

The method here described permits the sampling, transfer, and deter mination of respiratory gases in approximately 0.35 cmm. samples with errors not greater than ~0.2 volume per cent and in 0.07 c.mm. samples with errors not greater than ~0.5 volume per cent. It will handle up to 100 per cent absorbable gases. The analysis takes 4 to 6 minutes. The method is useful in general when only a minute quantity of gas can be used for analysis. This may involve cases in which it is desirable to analyze the composition or tension of gas occurring in an extremely small place, or cases in which one wishes to study the gas tensions in tissues ok fluids by introducing a minute gas bubble for equilibration. The micrometer burette, as applied to this method of analysis, utilizes the same principle as in micrometer burettes described earlier (l-3) ; namely, the displacement of mercury by means of a spindle which through a mercury-tight bearing freely moves into a mercury-filled burette chamber. The fact that the burette delivers without drainage error is a principal reason for its high accuracy. This burette utilizes a 0.304 mm. steel music wire as a micro spindle and displaces 0.0726 c.mm. per mm. This figure was determined both by calculating the volume of the spindle from its diameter and by weighing the total mercury delivered by 5 times 5 mm. advance of the spindle. If we designate the volume of 0.001 mg. ( = 1 y) of water as 1 r-liter, the smallest division on the micrometer ( = 0.01 mm.) corresponds to 0.726 y-liter ( = 0.0007 cmm.). So far the “y-burette” has been used only in the analysis of respiratory gases and blood gases (see the next paper). It can undoubtedly be used for other gases by selecting suitable absorbents and, with slight modification, for ultramicro titrations, in connection with a calibrated micro mercury pipette (see below). For other volumetric micro gas analytical procedures the reader is referred to papers by Krogh (4, 5), Scholander (2, 6), and Berg (7). Principle-The gas is sampled by means of a micro mercury pipette and is stored behind mercury in a glass transfer cup. From this cup it is drawn into a micrometer burette of approximately 1 c.mm. capacity. The gas sample is measured and extruded into a series of vials containing acid and fluids for the absorption of COZ and 02. The gas menisci are located by