Note on the loss of nitrogen and sulphur on drying faeces.

WHEN the collection of faeces during a metabolic experiment extends over a considerable period of time, difficulties arise in the determination of the total nitrogen and sulphur contents. Sampling of the wet composite specimen is generally unsatisfactory and ordinary methods of drying on a steam-bath result in a considerable loss of both nitrogen (as ammonia) and sulphur (mainly as sulphide). If nitrogen is the only element under consideration its loss as ammonia can be prevented by acidification with H2SO4 before drying. To obviate drying Van Slyke [1932] has recommended sampling from a suspension of the faeces in H2S04. If sulphur is also being determined, the excess of sulphuric acid which requires to be added masks the sulphur originally present in the faeces, and further, acidification leads to loss of H2S and certain organic sulphides on drying. The following experiments indicate the extent of the nitrogen and sulphur loss during drying. A method of preventing this loss is described.