and then to remove the solid particles which would otherwise foul the acid.  In carrying out this mechanical purification it was impossible, for two reasons, to make use of apparatus of the kind used in gas works; the first obstacle was the presence of solid particles carried forward by the gaseous currents, and the other difficulty was the volume of gas to be dealt with.  In the example to which the author’s attention was directed he had to purify 600 cubic meters of chimney gas per minute, or 36,000 cubic meters per hour, while the gas escaped from the flues at a temperature of from 400 deg. to 500 deg.  C. (752 deg. to 932 deg.  Fahr.), and a large quantity of cinders had frequently to be removed from the main chimney flues.  After many trials a simple appliance was constructed which successfully cooled the gases and freed them from ashes.  This consisted of a vertical screen, with bars three mm. apart, set in water.  This screen divided the gases into thin sheets before traversing the water, and by thus washing and evaporating the water the gases were cooled, and threw down the soot and ashes, and these impurities fell to the bottom of the water bath.  The gases after this process are divested of the greater part of any tarry impurities which they may have possessed, and are ready for the final purification, in which ammonia is extracted.  This is effected by means of a series of shallow trays, covered with water or weak acid, and pierced with a number of fine holes, through which the gas is made to bubble.  The washing apparatus is therefore strangely similar in principle to that designed by Mr G. Livesey.  M. Chevalet states that this double process is applicable to gas works as well as to the purification of smoke, with the difference that for the latter purpose the washing trays are filled with acid for the retention of ammonia, while in the former application gas liquor or water is used.  The arrangement is said to be a practical success.—­Journal of Gas Lighting.

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DETERMINATION OF NITROGEN IN HAIR, WOOL, DRIED BLOOD, FLESH MEAL, AND LEATHER SCRAPS.

BY DR. C. KRAUCH.

Differences obtained in the estimation of nitrogen in the above substances are frequently the source of much annoyance.  The cause of these discrepancies is chiefly due to the lack of uniformity in the material, and from its not being in a sufficiently fine state during the combustion.  The hair which is found in commerce for the manufacture of fertilizers, is generally mixed with sand and dust.  Wool dust often contains old buttons, pieces of wood, shoe pegs, and all sorts of things.  The flesh fertilizers are composed of light particles of flesh mixed with the heavier bone dust.