This superphosphate process has been at work at the South Metropolitan Gas Works, Old Kent Road, for nearly two years.  In practice it is usual to water the superphosphate before use with ammoniacal liquor, and it is used in dry purifiers, in layers about eight inches thick.

This process has been thoroughly investigated at the Munich Gas Works, by Drs. Bunte and Schilling, and the report made by these gentlemen proves its practical efficiency, and therefore the question of its advantage, as compared with washing and scrubbing, is based chiefly upon financial considerations.  It is evident that in foreign parts, or in any place where there is a difficulty in disposing of the ammonia, the obtaining of the same in a dry form offers several advantages as compared with having it as a weak solution.

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RECONVERSION OF NITRO-GLYCERIN INTO GLYCERIN.

By C.L.  BLOXAM.

The following experiments on this subject appear to possess some interest at the present moment: 

1.  Nitro-glycerin was shaken with methylated alcohol, which dissolves it readily, and the solution was mixed with an alcoholic solution of KHS (prepared by dissolving KHO in methylated spirit, and saturating with H_{2}S gas).  Considerable rise of temperature took place, the liquid became red, a large quantity of sulphur separated, and the nitro-glycerin was entirely decomposed.

2.  Nitro-glycerin was shaken with a strong aqueous solution of commercial K_{2}S.  The same changes were observed as in 1, but the rise of temperature was not so great, and the liquid became opaque very suddenly when the decomposition of the nitro-glycerin was completed.

3.  The ordinary yellow solution of ammonium sulphide used in the laboratory had the same effect as the K_{2}S.  In this case the mixture was evaporated to dryness on the steam bath, when bubbles of gas were evolved, due to the decomposition of the ammonium nitrite.  The pasty mass of sulphur was treated with alcohol, which extracted the glycerin, subsequently recovered by evaporation.  Another portion of the mixture of nitro-glycerin with ammonium sulphide was treated with excess of PbCO_{3} and a little lead acetate, filtered, and the ammonium nitrite detected in the solution.  These qualitative results would be expressed by the equation—­

       C3H5(NO)+3NH4HS = C3H5(OH)3 + 3NH4NO2 + S3,

which is similar to that for the action of potassium hydrosulphide upon gun-cotton.

4.  Flowers of sulphur and slaked lime were boiled with water, till a bright orange solution was obtained.  This was filtered, and some nitro-glycerin powered into it.  The reduction took place much more slowly than in the other cases, and more agitation was required, because the nitro-glycerin became coated with sulphur.  In a few minutes, the reduction appearing to be complete, the separated sulphur was filtered off.  The filtrate was clear, and the sulphur bore hammering without the slightest indication of nitro-glycerin.