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152 unperceived way into the experiments, they will still show the extreme delicacy of heat, or heat and potash, as a test of its presence by the formation of ammonia.

With respect to the delicacy of the test, it may be observed that it offers many facilities to the detection of nitrogen when in certain states of combination, which chemists probably were not before aware of. A portion of asbestos, which had been heated red-hot, was introduced into a tube by metallic forceps and heated; it gave no ammonia; another similar portion, compressed together, and introduced by the fingers, gave ammonia when heated. A very minute particle of nitre was dropped into hydrate of potassa, and heated to dull redness; it gave no ammonia; a small piece of zinc-foil, dropped in and the heat applied, caused an abundant evolution of that substance.

The circumstance also of absorption by lime and other bodies, of something from inhabited atmospheres, which yields ammonia when thus tested, is very interesting; and Dr. Paris has suggested to me that this power may probably be applicable to the examination of the atmosphere of infected and inhabited places, and may perhaps furnish the means of investigating such atmospheres upon correct principles.

February. 17, 1825.

are many fluids in the laboratory which are much more conveniently retained in tubes, such as that depicted, fig. 5, plate I, than in bottles, and from which they may be taken in a less wasteful manner when required for the purpose of experiment. A piece of glass tube, a quarter of an inch or more in diameter, being selected, is to be closed at one end by the blowpipe; and then, being softened near the other end, is to be drawn out obliquely, so as to form the long narrow neck represented in the figure, but to which, in, the first case, the short piece of tube is to be left attached; this forms a funnel, into which the preparation to be preserved is to be put. Then, warming the body of the tube, the expanding air passes