Apparatus for the Continuous Drying and Extraction of Biological Materials. Ap- Plication to the Extraction of the Neutral Fat Fraction of Feces

The extraction of liquid or moist biological materials almost invariably involves preliminary drying of the sample. This is usually accomplished by heating the finely divided specimen on a steam bath or in a drying oven at 1055110’. The length of time necessary for complete dehydration depends upon the surface exposed, the temperature of drying, and the circulation of air above the material. One method of insuring (1) complete desiccation involves the addition of a volatile water-soluble solvent after the sample has been dried sufficiently to be powdered, and then heating to drive off the solvent. Final traces of moisture are then removed after the sample has stood for several days in a vacuum desiccator. It is quite apparent that these procedures are open to several serious objections. In the first place, the analyst can never be certain that his sample is absolutely free of water. Water and steam pockets are frequently encountered. Prolonged heating may cause decomposition. Volatile solvents added to aid drying usually extract fats which deposit on the walls of the drying vessel and the final product is not truly homogeneous in composition. As a consequence of the many precautions which are thus taken, the process of drying involves a considerable expenditure of time. Days, and sometimes weeks, are required for an analysis involving a preliminary drying. Then, too, analyses of very fatty substances are a problem in themselves. A gummy product results, one which contains water bound in such a fashion that it