TRANSACTIONS OF SECTION B. 743 
of the steam formed by the reaction, which gave rise to the formation of a con- 
siderable quantity of hydrochloric acid on treatment with hot air. In conjunction 
with Dr. Eschellman (who carried out the experiments for me), I succeeded in 
reducing the quantity of this hydrochloric acid to a negligible amount by adding 
to the magnesia a certain amount of chloride of potassium, which probably has the 
effect of forming an anhydrous double chloride. 
This mixture of magnesia and potassium chloride is, after the addition of a 
certain quantity of china clay, made into small pills in order to give a free and 
regular passage throughout their entire mass to the hot air and other gases with 
which they have to be treated. In order to avoid as far as possible the handling 
and consequent breaking of these pills, I vapourise the ammonium chloride in a 
special apparatus, and take the vapours through these pills and subsequently pass 
hot air through. and then again ammonium chloride vapour, and so on, without 
the pills changing their place. 
The vapourisation of the ammonium chloride is carried out in long cast-iron 
retorts lined with thin Doulton tiles, and placed almost vertically in a furnace 
which is kept by producer gas at a very steady and regular temperature. These 
retorts are kept nearly full with ammonium chloride, so as to have as much active 
heating surface as possible. From time to time a charge of ammonium chloride is 
introduced through a hopper at the top of these retorts, which is closed by a nicke} 
plug. The ammonium chloride used is very pure, being crystallised out from its 
solution as produced in the ammonia soda manufacture by a process patented by 
Mr. Gustav Jarmay, which consists in lowering the temperature of these solutions 
considerably below 0° C. by means of refrigerating machinery. The retorts will 
therefore evaporate a very large amount of ammonium chloride before it becomes 
necessary to take out through a door at their bottom the non-volatile impurities which 
accumulate in them. The ammonium chloride vapour is taken from these retorts 
by cast-iron pipes lined with tiles and placed in a brick channel, in which they are kept 
hot, to prevent the solidification of the vapour, to large upright wrought-iron cylin- 
ders which are lined with a considerable thickness of fire-bricks, and are filled with 
the magnesia pills, which are, from the previous operations, left at a temperature 
of about 800°C, On its passage through the pills the chlorine in the vapours is 
completely retained by them, the ammonia and water vapour formed pass on and 
are taken to a suitable condensing apparatus, The reaction of the ammonium 
chloride vapour upon magnesia being exo-thermic, the temperature of the pills 
rises during this operation, and no addition of heat is necessary to complete it. 
The temperature, however, does not rise sufficiently to satisfactorily complete the 
second operation, viz., the liberation of the chlorine and the re-conversion of the 
magnesium chloride into magnesium oxide by means of air. This reaction is. 
slightly endo-thermic, and thus absorbs a small amount of heat, which has to be 
provided in one way or another. I effect this by heating the pills to a somewhat 
higher temperature than is required for the action of the air upon them, viz., to 
600° C., by passing through them a current of a dry inert gas free from oxygen 
heated by a Siemens-Cowper stove to the required temperature. I use for this 
purpose the gas leaving the carbonating plant of the ammonia soda process. 
This current of gas also carries out of the apparatus the small amount of 
ammonia which was left in between the pills. It is washed to absorb this 
ammonia, and after washing this same gas is passed again through the Siemens- 
Cowper stove, and thus constantly circulated through the apparatus, taking up the 
heat from the stove and transferring it to the pills. When these have attained the: 
required temperature, the hot inert gas is stopped and a current of hot air passed 
through, which has also been heated to 600° C. in a similar stove. The air acts: 
rapidly upon the magnesium chloride, and leaves the apparatus charged with 18 to: 
20 per cent. of chlorine and a small amount of hydrochloric acid. The chlorine 
comes gradually down, and when it has reached about 3 per cent. the temperature: 
_ of the air entering the apparatus is lowered to 350° C. by the admixture of cold 
air to the hot air from the stove; and the weak chlorine leaving the apparatus is 
passed through a second stove, in which its temperature is raised again to 600° C., 
and passed into another cylinder full of pills which are just ready to receive the 
