—

Factory.
Week.I.II.III.IV.V.VI.
1st36·937·836·736·336·636·6
2nd36·136·836·736·235·137·4
3rd36·538·036·636·137·237·9
4th35·937·135·936·236·837·1
5th35·836·936·036·336·537·8
6th36·037·036·235·936·537·2
7th36·536·036·336·635·836·8
8th36·336·836·336·335·037·1
9th36·436·336·835·735·237·0
10th36·536·736·336·036·237·6
11th36·836·836·235·936·037·2
12th36·835·935·635·636·137·2
13th36·735·235·936·136·937·5

Spite of the expensive plant required to work Mr Weldon’s process, it is said to possess very decided advantages over the old methods as far as regards cost of production.

In connection with Mr Weldon’s process may be mentioned Mr Valentin’s modification of it, for which a provisional patent was taken out by this latter gentleman. Instead of adding more lime, after the neutralised still liquors have been precipitated by an equivalent of lime, as is done in the above process, Mr Valentin adds a solution of potassium ferricyanide, and air being blown in, the peroxidation of the manganese is effected much more quickly than in Mr Weldon’s process. It was also calculated that, by Mr Valentin’s method, bleaching powder could be produced at a cost of about ten shillings per ton less than when made by Mr Weldon’s.

For the successful working of Mr Valentin’s process it is necessary that the ferricyanide should be recovered, not only because of its cost, but also because its presence gives rise to the production of cyanogen compounds, which would enter the chamber with the chlorine. Hitherto no economical plan for the recovery of the salt has been devised, and consequently Mr Valentin’s proposed modification of Mr Weldon’s process has failed to be adopted.

b. A second process for obtaining chlorine, called “the magnesia process,” has been devised by Mr Weldon. In the previous method, or “lime process,” two thirds of the chlorine contained in the hydrochloric acid, as we have seen, is lost, passing away in the form of waste chloride of calcium.

In the “magnesia process” all the chlorine is utilised, the acid employed being made to yield the whole of its gas in the free state. The regeneration of the manganese peroxide being likewise accomplished, and the process being a continuous one, theoretically no loss of material should take place.

Beyond the employment of liquor pumps, no machinery is requisite for carrying out the operation, which, being very simple in its details, requires the employment of little skilled and, consequently, expensive labour. Further, the inventor claims for it the production of bleaching powder at a less cost per ton than by any other process. The “magnesia method” is worked as follows:—

The spent liquors of the still, consisting of chloride of manganese and free hydrochloric acid, are neutralised with magnesite, or, as it is sometimes called, Greek stone—a very pure native form of carbonate of magnesia. Sometimes the magnesite is calcined, and the magnesia thus obtained used instead.

The neutralisation may be effected either in the still itself, or in a well made of cast iron. The liquid is next pumped into the settlers, in which it deposits its ferric and aluminic oxides and sulphate of lime. The clear liquor containing the chlorides of manganese and magnesia is then run into an iron evaporating pan, where it is concentrated by boiling until it reaches a temperature of between 300° and 320° F. At this point the magnesium chloride begins to be decomposed by the water, and hydrochloric acid is given off. When it has reached the above degree of concentration, it is conveyed into a muffle furnace. This furnace is divided into two compartments, separated by an iron door, which can be opened or shut by means of a pulley placed outside. The desiccation of the mass which is accompanied with the evolution of a little chlorine and a large amount of hydrochloric acid, having been completed in one of the divisions of the furnace, it is broken up by constant stirring into thin cakes and raked into the second division, where it is gently heated with access of air; when the operation is complete the residue which left the first compartment as a mixture of manganese and magnesium chloride becomes converted into manganate of magnesia (MgMnO3), its chlorine having been driven off partly in the free state and partly as hydrochloric acid. “As long as water is present in the furnace hydrochloric acid is evolved, and as the main evaporation takes place in the first division of the furnace, it is chiefly hydrochloric acid that is there generated. In the second division it is chiefly chlorine which is evolved, but it is, of course, mixed with some hydrochloric acid. It is, indeed, doubtful whether much manganese chloride is decomposed by the water so long as there remains any chloride of magnesium, as this body is far more readily decomposable.”[242]