Boiling point °C.Mm. Caled.

In a series of experiments combustion cycles for the analysis of a rather wide range of compound types were determined, using a semiautomatic combustion unit.The unit is described and the conclusions drawn from its operation are applied to fully automatic units now in routine use. The combustion cycles employed are compared with those of other automatic units previously described. INTHE microdetermination of carbon and hydrogen in organic compounds, a combustion unit which operates automatically shows important advantages over the conventional, manually operated apparatus. Stated briefly, the more outstanding advantages are:1. One analyst can operate two units simultaneously; if only one unit is in operation, he is free to attend to other duties.2. Combustion conditions can be held essentially constant, to give extremely uniform analyses.3. Since the human factor has been minimized, inexperienced or untrained personnel can perform better analyses than are possible using a manually operated outfit.Two automatic combustion units for the microdetermination of carbon and hydrogen have been described in the literature ($, 6). Although in each case it was indicated that satisfactory analyses could be obtained, no extensive experimental data were given upon which to base a fair comparison of automatic and manual methods from the standpoint of accuracy and precision. Because of the lack of such data, and because of the wide variety of samples to be analyzed in this laboratory, it seemed advisable not to construct a fully automatic apparatus at the outset, but to start with what might be called "semiautomatic" operation. In this type of unit the movable vaporization furnace is advanced by means of a motor-driven rotating screw, the rate of advance being controlled by the analyst rather than by mechanical means.A successful semiautomatic unit was developed, and combustion cycles adaptable to the rapid analysis of samples covering a wide range of compositions were determined. The fully

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