[242] Kingzett.
It is stated that all the manganese is not converted into peroxide in the furnace, but that a certain portion of it is left as protoxide; which, with the magnesia, constitutes the useless “bases.” The completion of the process is known when portions of the cake drawn from time to time from the furnace cease to indicate any increase in the quantity of peroxide of manganese.
The finely-divided black powder—manganate of magnesium—thus obtained, after leaving the furnace and when sufficiently cold, is ready for the stills—where, in contact with hydrochloric acid, it is again employed in the generation of chlorine.
The chlorine leaves the furnace mixed with much hydrochloric acid, nitrogen, and air. The gaseous mixture is drawn by a chimney draught through the coke towers, as in the making of salt-cake. By this contrivance the hydrochloric acid is recovered, yielding a solution strong enough to react upon fresh manganese in the still. The diluted chlorine may be made to ascend leaden towers, where it comes in contact with a shower of milk of lime, which absorbs the gas and forms ordinary bleaching liquid, whilst sometimes it is employed in the production of potassium chlorate.
We have seen that the chlorine yielded by the “magnesia process” is partly in the concentrated, and partly in the dilute condition. The ratio of strong chlorine generated in the still to that of weak chlorine produced in the furnace may be anything between one to one, and one to about four, at pleasure.
“When working so as to obtain strong chlorine and weak chlorine in about equal proportions, the quantity of the liquor to be boiled down per ton of total bleaching powder made was about 105 cubic feet. As the proportion of the weak chlorine increased, the quantity of liquor to be boiled down diminished until, when the proportion of the weak chlorine to that of the strong became as four to one, the quantity of liquor to be boiled down per ton of total bleaching powder made was only about 40 cubic feet.”[243]
[243] ‘Chemistry, Theoretical, Practical, and Analytical,’—Mackenzie & Co.
11. (Deacon.) As we have already seen, Vogel proposed to obtain chlorine by the decomposition by heat of cupric chloride, and to reconvert the resulting cuprous chloride into the cupric salt by treatment with hydrochloric acid.
Chlorine may be produced by passing a mixture of gaseous hydrochloric acid and air over heated bricks or other porous substances, a reaction which Oxland unsuccessfully attempted to turn to account for the production of chlorine for manufacturing purposes. The cause of failure appears to have been the great heat necessary to effect the decomposition of the acid atmospheric oxygen.
In the late Mr Deacon’s process both Vogel’s and Oxland’s methods are combined. He discovered that to be able to generate chlorine and water from gaseous hydrochloric acid and air, a very much lower temperature than that employed by Oxland was necessary, and he found that this diminished temperature could be attained, if the gas and air to be decomposed were passed over porous bricks saturated with a solution of sulphate of copper, and heated to a temperature of 700° to 750° F.