of the borohydride before reaction with the aldehyde, and the error can be eliminated if the solvent is made Q.01AÍ in sodium hydroxide. The n-alkyl aldehydes react rapidly enough that the hydrolysis is negligible even in the absence of base. In each case where sodium hydroxide was used, a sample of the aldehyde was allowed to stand in the Q.OlAf base at 45°C. for 30 minutes before titration, and in no case were the titration results significantly different from those in which the aldehyde was titrated immediately.Furfural and o-me thoxy benzaldehyde, even when titrated in base at 45°C ., gave high results because of the slowness of the borohydride reduction.Cinnamaldehyde, p-hydroxybenzaldehyde, p-dimethylaminobenzaldehyde, vanillin, and anisaldehyde were even more unreactive and could not be determined by this titration procedure.Presumably, any of the aldehydes listed by Jensen (1) as having a rate constant less than 40 liter mole-1 minute-1 would also be too unreactive for accurate titration, Formaldehyde, hemiacetalforming aldoses, and other compounds which do not show the characteristic carbonyl absorption peak in water can not be determined by this method since no change in absorbance can be detected.Peroxides and some ketones will cause serious interference in the method. Ketones in general are much less reactive toward borohydride than are aldehydes but certain ketones such as acetone and cyclohexanone are readily reduced. Less reactive ketones such as methyl hexyl ketone or acetophenone will not cause interference unless their concentration greatly exceeds that of the aldehyde being determined.Compounds containing acidic hydrogen atoms will decompose the borohydride titrant, but these may be neutralized before titration is initiated.Functional groups which are not reduced" by borohydride in this medium include anhydrides, esters, amides, imides, acetals, nitriles, halides, and carbon-carbon double bonds. LITERATURE CITED(1) Jensen, E. ., "A Study on Sodium Borohydride," Nyt Nordisk Forlay

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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Under routine analytical conditions the Abrahamczik type of absorption tubes, with minor structural modifications, compared favorably with those of Pregl design in accuracy, ease of handling, and absorption capacity. In addition, they were practically unaffected by high or low humidity, changes in temperature, or standing idle THE Pregl type of absorption tube seems to be used most generally in the combustion of organic compounds for the microdetermination of carbon and hydrogen. The disadvantages of this type of tube are apparent to all who have used them extensively. Unless the atmosphere of the laboratory is controlled in such a way as to place the relative humid-