THE ALUMNI JOURNAL. 



313 



lie found that magnesia alone would 

 answer the purpose without the pres- 

 ence of the peroxide of mangan- 

 ese. He obtained the assistance of M. 

 Pechiney, of Salindres, and in conjunct- 

 ion with him worked out what has be- 

 come known as the "Weldon-Pechiney'' 

 process, which was first patented in 1884. 

 This process consists in neutralizing 

 muriatic acid by magnesia, concentrating 

 the solution to a point at which it does 

 not yet give off any hydrochloric acid, 

 and then mixing it into a fresh quantity 

 of magnesia so as to obtain a solid oxy- 

 chloride of magnesium. This is broken 

 up into small pieces, which are heated 

 up rapidly to a high temperature with- 

 out 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 elim- 

 inate the steam and the acid from the 

 chlorine. The acid condensed is, of 

 course, treated with a Iresh quantity of 

 magnesia, so that the whole of the chlo- 

 rine which it contains is gradually ob- 

 tained in the free state. 



The rapid heating to a high tempera- 

 ture of the oxychloride of magnesium 

 without contact with the heating medium 

 was an extremely difiBcult 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 ar- 

 ranged that they could all be filled from 

 the top of the 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 

 the magnesium oxychloride, with which 

 the chamber was filled when hot enough. 

 Mr. Weldon himself called this ap- 

 paratus a "baker's oven," in which 

 trade certainly the same principle had 

 been employed from time immemorable; 

 but to my knowledge it had never be- 

 fore been used in any chemical industry. 

 This process has been at work at M. 

 Pechiney 's large alkali works at Salin- 

 dres and is now at work in this country 

 at the chlorate of potash works of 

 Messrs. Allbright & Wilson, at Oldbury, 

 a manufacture for which it offers special 

 advantages. Mr. Weldon and M. Pechi- 

 ney had expected that this process would 

 become specially useful in connection 

 with the ammonia soda process by pre- 

 paring in the way proposed by Mr. 

 Solvay and Mr. Weldon in 1872, a 

 solution of magnesium chloride as a 

 by-product of this manufacture, but in- 

 stead of obtaining muriatic acid from this 

 solution by Clemm's process to treat it b}^ 

 the new process, so as to obtain the bulk 

 of the chlorine at once in the free state. 

 But M. Pechiney did no more succeed 

 than his predecessors in recovering the 

 ammonia by means of magnesia in a satis- 

 factory 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 re- 

 covers the ammonia, as usual, by means 

 of lime, and converts the solution of 

 chloride of calcium, obtained by a pro- 

 cess patented by I^Ir. Weldon in 1869, 

 viz.; by treatment with magnesia and 

 carbonic acid under pressure, into chlor- 

 ide of magnesium with the formation of 

 carbonate of lime. The magnesium 

 chloride solution is then concentrated 



