(Mn,O,); but, as before said, if this oxidation be effected. in the presence of ferricyanide of potassium, peroxide of manganese (MnO2) is produced. Mr. Valentin explains this as a process in which the ferricyanide acts as a carrier of oxygen, and it is instructive to compare this reaction with other similar ones known to chemical science.

Suboxide of copper, or cuprous oxide Cu2O, is a red body, and tolerably stable in the pure state at normal temperatures. When dry, it passes into a higher state of oxidation if heated to a temperature considerably above 100° C. If placed in water and submitted to a current of air or oxygen, it is unaffected, as the author has shown; but the presence of a small quantity of a caustic alkali under these conditions induces a peroxidation even in the cold, and more rapidly in the hot; and in this way the red lower oxide is transformed into the black oxide, CuO. Here, therefore, the alkali acts as a carrier of oxygen, and this hypothesis derives considerable support from Harcourt's discovery of higher oxides of potassium and sodium than those which form the base of ordinary caustic alkaline solutions. It is, therefore, to be supposed that in the above reaction the oxide of sodium or potassium is, for the time being, continually peroxidised and reduced, yielding the oxygen thus carried to the oxide of copper.

There are many such continuous actions,' as they are called, in chemistry. As we have seen in a previous chapter, sulphuric acid is manufactured by a process in which an oxide of nitrogen acts as a carrier of oxygen to sulphurous anhydride, and there is practically attempted, and partially realised, what theoretically takes place, viz., the transformation of an infinitely large amount of sul

phurous anhydride into sulphuric acid, by means of an indefinitely small quantity of nitric acid.

The process by which ordinary ether is made, is another similar and striking instance of this class of reactions, and may be expressed as the conversion of an infinitely large amount of alcohol into ether, by means of an indefinitely small quantity of sulphuric acid. Thus the process is supposed to take place in two distinct phases, and that this truly represents what actually occurs, has become almost matter of certainty, through some elaborate researches of Williamson.

(1) H2SO4+C2H2HO=C2H2HSO4 + H2O

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(2) C2H2HSO4 +С2H¿HO=(C2H5)2O+H2SO4·

In the next chapter we shall consider an improved form of Mr. Weldon's process as here described.

CHAPTER XV.

WELDON'S MAGNESIA CHLORINE PROCESS (b).

THE success attending Weldon's process for the manufacture of chlorine gave an impetus to researches in chemical industry, and one result was the perfection of another method for making chlorine devised by Mr. Deacon of Widnes. This process we shall describe in the next chapter.

Here we shall record those efforts made by Mr. Weldon to perfect his own process by the substitution of magnesia (to be recovered) in the place of lime.

These experiments must be regarded as highly successful, and showed that the process admitted of many modifications, none of which, however, have been adopted by manufacturers for one reason, viz., because they were satisfied with the results obtainable with the old form of the process.

Should an increased demand for bleaching powder arise, it is not unlikely that the process now to be described will come into use.

The process commences by neutralising the acid liquor from the stills, formed by the action of hydrochloric acid on native manganese, with Greek stone or very nearly pure magnesite (carbonate of magnesium). Or, if it be desirable, the Greek stone may be first calcined and the light, easily-dissolved magnesia powder, so

made, used in its stead. This operation is performed in a well of cast-iron, or the liquor may be neutralised in the stills.

The mixed chlorides of manganese and magnesium liquor, obtained as described, is pumped into the settlers, where any peroxide of iron, alumina and gypsum deposit. This gypsum is derived from the sulphuric acid contained in commercial hydrochloric acid. From the settlers the liquor is run into an iron pot or pan, where it is evaporated until it attains a state of concentration, registering a temperature of about 320° Fahr. At this stage the evolution of hydrochloric acid gas commences, from the decomposition of the magnesic chloride by water. By opening a screw plug (of metal) it is now run into a muffle furnace, consisting of two divisions, which communicate with each other by means of an iron door worked by a pulley from without.

In one of these compartments the evaporation to dryness is completed, and is accompanied by the evolution of much hydrochloric acid, plus a little chlorine. The residue, which, by stirring constantly at this stage, is broken up into thin cakes, is then transferred by means of a rake into the second compartment, where it is heated with access of air.

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Here the heat requires careful regulation, for if the temperature rises too high, fusion ensues, and thus the porosity of the mass is lost and oxidation impeded. The best heat is one designated blood-red,' and if this be attained and kept, the oxidation proceeds very regularly till the end. This tendency to fuse on the part of the mixture is due to the magnesic chloride, and therefore it is greater in the first place than afterwards, when it is

partially decomposed, as magnesia exhibits no such disposition. In other words, the furnace may be brightly red hot in the first compartment, because the temperature is greatly reduced by the evaporation which there takes place. As the mixture passes into the second compartment of the furnace, it consists of manganese chloride, together with magnesic chloride and magnesia, hence it is at this stage, that the temperature must be carefully watched ; but as the decomposition proceeds, the magnesic chloride becomes less and less in quantity, and therefore the temperature may be allowed to increase to some extent with the decomposition. At the same time that the magnesium chloride undergoes decomposition, so also does the manganic chloride, and there is thus obtained protoxide of manganese, which absorbs oxygen from the air which is admitted, and becomes peroxide. This latter body appears to combine with the magnesia under these circumstances, and forms what Mr. Weldon has termed manganite of magnesium (MgMnO3), which when properly made, is a dense, black, finely divided powder. It should be understood, however, that all the manganese is not peroxidised, in short, that there remains a certain portion as protoxide, and this, with the magnesia, constitutes what is termed the base,' that is, it furnishes with hydrochloric acid no free chlorine. It is only the manganese which exists as peroxide, that is capable of liberating chlorine in the stills. Now, so 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 which is there generated. In the second division it is chiefly chlorine

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