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TRANSACTIONS OF SECTION B. 741 
Mr. Weldon, when he decided to give up his manganite of magnesia process, 
by no means relaxed his efforts to work out a chlorine process which should 
utilise the whole of the muriatic acid. While working with manganite of 
magnesia he found that magnesia alone would answer the purpose without the 
presence of the peroxide of manganese. He obtained the assistance of M. Pechiney, 
of Salindres, and in conjunction with him worked out what has become known as 
the ‘ Weldon-Pechiney ’ process, which was first patented in 1884. 
This process consists in neutralising muriatic acid by magnesia, concentrating 
the solution to a point at which it does not yet give off any hydrochloric acid, and 
then mixing into it a fresh quantity of magnesia so as to obtain a solid oxychloride 
of magnesium. This is broken up into small pieces, which are heated up rapidly to a 
high temperature without contact with the heating medium, while a current of 
air is passing through them. The oxychloride of magnesium containing a large 
quantity of water, this treatment yields a mixture of chlorine and hydrochloric 
acid with air and steam, the same as the Deacon process, and this is treated in a 
very similar way to eliminate the steam and the acid from the chlorine. The acid 
condensed is, of course, treated with a fresh quantity of magnesia, so that the 
whole of the chlorine which it contains is gradually obtained in the free state. 
The rapid heating to a high temperature of the oxychloride of magnesium with- 
out contact with the heating medium wasan extremely difficult practical problem, 
which has been solved by M. Pechiney and his able assistant, M. Boulouvard, in a 
very ingenious and entirely novel way. 
They lined a large wrought-iron box with fire-bricks, and built inside of this 
vertical fire-brick walls with small empty spaces between them, thus forming a 
number of very narrow chambers, so arranged that they could all be filled from 
the top ofthe box, and emptied from the bottom. These chambers they heated to 
a very high temperature by passing a gas flame through them, thus storing up in 
the brick walls enough heat to carry out and complete the decomposition of tke 
magnesium oxychloride, with which the chamber was filled when hot enough. 
Mr. Weldon himself called this apparatus a ‘baker's oven, in which trade 
certainly the same principle has been employed from time immemorial; but to my 
knowledge it had never before been used in any chemical industry. This process 
has been at work at M. Pechiney’s large alkali works at Salindres, and is now at 
work in this country at the chlorate of potash works of Messrs. Allbright and 
Wilson at Oldbury, a manufacture for which it offers special advantages. Mr. 
Weldon and M. Pechiney had expected that this process would become specially 
useful in connection with the ammonia soda process by preparing in the way pro- 
posed by Mr. Solvay and Mr. Weldon in 1872 a solution of magnesium chloride 
as a by-product of this manufacture, but instead of obtaining muriatic acid from 
this solution by Clemm’s process, to treat it by the new process, so as to obtain the 
bulk of the chlorine at once in the free state. But M. Pechiney did no more suc- 
ceed than his predecessors in recovering the ammonia by means of magnesia in a 
satisfactory way. 
Quite recently, however, it has been applied to obtain chlorine in connection 
with the ammonia soda process by Dr. Pick, of Czakowa, in Austria, He recovers 
the ammonia, as usual, by means of lime, and converts the solution of chloride of 
calcium, obtained by a process patented by Mr. Weldon in 1869, viz., by treatment 
with magnesia and carbonic acid under pressure, into chloride of magnesium with 
the formation of carbonate of lime. The magnesium chloride solution is then con- 
centrated and treated by the Weldon-Pechiney process. 
I have repeatedly referred during this brief history to the great change which 
has been brought about in the position of chlorine manufacture by the develop- 
ment of the ammonia soda process, and have pointed out that the muriatic acid 
which for a long time was the by-product of the Le Blanc process, without value, 
thereby became gradually its main and most valuable product, while the alkali 
became its by-product. 
I have told you how, very early in the history of this process, Mr. Solvay and 
_ Mr. Weldon proposed means to provide for this contingency, and how Mr. Weldon 
continued to improve these means until the time of his death, Mr. Solvay, on his 
