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acid flowing at all times can be seen at a glance. The top of the tower is closed with a plug screwed therein and tapped for a two-inch pipe which extends upward to a small cast iron cylinder, 3′ high and 18" diameter, provided with two oblong openings directly opposite each other, 3′′ wide and 6′′ high, for insertionof panes of glass.
The two lines conveying the oleum and weak acid respectively, enter the two blind sides of the cast iron cylinder, their ends being bent so that the acid leaves the pipes in a direction parallel to the sides of the tower and directly in the line of light between the two panes of glass in the sides of the little cylinder, thus there is in plain sight at all times the amount of acid flowing from each pipe; while at the same time no fumes of SO, are present to obscure the vision due to the absence of air saturated with moisture. The streams drop into a round heavy crockery dish resting on the bottom of the cylinder. The partially mixed acid overflows the edge of the bowl to the bottom of cylinder from which it is conveyed to the top of the tower, down through which it flows over the quartz packing, being thoroughly mixed by flowing over the quartz. The acid can also be thoroughly freed from SO2, and a great deal of its objectionable color by blowing a current of air up through the tower.
The top rim of the cast iron mixing cylinder is flanged and to this the top is bolted, using asbestos gaskets to secure an air tight joint. This tower is simple, cheap and with a little attention will perform its work perfectly, requiring only a few minutes' attention now and then. If sufficient receivers are at hand to permit continuous operation it will deliver acid of desired Beaumé (60° Bé or 66° Bé) at not more than 10° F. above temperature of inflowing cooling water.
The pipe conveying the acid from the cast iron mixing cylinder to the tower can also be water jacketed if greater cooling efficiency is desired. Fig. I shows the mixing tower. There should be a tap or washout valve on the bottom of the water jacket for the removal of the dirt, sediment, etc., which will be deposited there. This can readily be removed by closing valve on the water outlet and forcing water and sediment out through the washout valve, thus thoroughly clearing the bottom of the water jacket of any deposited sediment. With proper care the tower will last indefinitely and the wrought iron shell being much thinner and more homogenous than cast iron, its cooling efficiency is proportionately just so much greater. The expense of construction is so small that it could be installed even if only needed occasionally.
There is great trouble at times, especially during the summer months in keeping the oleum up to a proper strength (i. e. 105% H2SO, or over). The trouble is often caused by the decreased efficiency of the devices for cooling the roaster gases, due for the most part to the increased temperature of the water and also to less cooling of the acid in the absorption towers due to increased temperature in the building. The best temperature at which to
keep the acids in the No. 1, 2 and 3 towers for the production of strong oleum (105% H, SO, and over) is between 70 and 80° F., as enormous absorption seems to take place at this temperature and comparatively little dissociation, even when the oleum becomes quite strong. This temperature can be obtained as follows: The ordinary cooler consists simply of a hollow wrought iron cylinder, 21⁄2' diameter and 20' high, with hot gases flowing through inside and water running down the outside which is crude and remarkably inefficient in summer, as the quantity of water that can be used is not much owing to excessive splashing. The cooling efficiency can be greatly increased as follows (see Fig. 2):
The cooler is built up of three concentric wrought iron tubes, the outer shell being 20' high, 32' diameter at the bottom and tapering to a diameter of 3' at the top. The two inner tubes are respectively 18′′ and 16" in diameter and 16′ long, riveted or screwed at their ends to annular castings and forming between the inside surface of the larger tube and outside surface of the smaller tube a circular space, 2" in diameter and 16′ high, which is at all times kept full of running water by means of a supply pipe entering the top casting, with exit in bottom casting, which rests on a heavy cast iron ring supported by four heavy legs cast thereon, thus raising bottom of inside cooler 2' from bottom of cooler and forming an open space that permits the passage of the hot gases either inside or outside the inner ring cooler with a similar open space at the top. The top casting is tapped for a small pipe to allow escape of air when filling inner cooling chamber and, so placed that there will be a continuous discharge of water from its end, thus insuring that the inner chamber is always full of running water.
The arrows indicate the path of the gases. As will be readily, seen, the hot gases as they enter the bottom of the cooler have more room due to the slope of the outer jacket or tube and at the top as the gases contract on cooling the space is also smaller, thus giving a better chance for the imparting of the last portion of heat in the gas to the entering cold water in both coolers. It will be found that the gases leaving a cooler of this construction will be not over 80° F. (hand warm), a temperature that it is impossible to attain by the use of the present coolers. Another advantage of the inner ring cooler is that it cools the gases both from within and without, thus leaving a very short path between cooling surfaces.
With this cooler and a very simple cooler for cooling the oleum, there is no difficulty in keeping the strength of the oleum in the first tower between 105 and 106% H2SO..
In conclusion, the writer would say that if the sizes of the units is increased, the present costly makeshifts are replaced by up-to-date serviceable devices and the whole plant put in charge of resourceful men, backed by not too timid capital, it would be but a short time until the production of sulphuric acid by the chamber system (except as a source of supply for the contact systems) would become a thing of the past. Undoubtedly,
the present day contact processes, crude as they are, possess many basic advantages over the chamber systems. In the first place, all towers, blowers, tanks, filters, coolers, retainers and in fact all the various acid retaining vessels, pipes, etc., are of wrought iron, cast iron or steel, which with reasonable care and attention will last indefinitely. There is not a pound of lead in any shape or form used in the whole system. This, in itself, is an immense advantage, as all know who have had any experience with lead chambers that are beginning to get old and thin. The first cost of lead over cast iron is also far greater. Secondly, there is the item of the purification of chamber acids, when using arsenical pyrites, which is an item of considerable importance and expense. This is entirely and automatically done by the iron contact shaft. Third, there is also the expense of the concentration of the weak chamber acid, which can be entirely removed, as the contact system has been supplied for a long time with purified chamber acid of 50° Bé, with high yields on sulphur burnt. Fourth, the advantage of producing acid of any strength desired, as outlined in the beginning of this article at practicallly no expense whatever. Fifth, the elimination of the use of platinum as a catalytic agent altogether and combining the contact and chamber systems, producing both strong oleum and arsenic free sulphuric acid from the same system, a result which has been successfully demonstrated on a practical scale. a practical scale. Sixth, the total elimination of the charge for saltpeter, which, under most favorable circumstances does not fall much under two per cent of the total sulphur burnt, and in itself one of the largest items in the manufacture of acid by the chamber process. There is also the great advantage of compactness in the contact process.
It goes without saying that a great deal depends upon "the man behind the gun," for if the foreman or whoever has charge of the system is not observant, careful and pays no attention to various little things, there is sure to be trouble with this system, as with all systems under the supervision of just such men. (To be continued1).
In the manufacture of the bauxite fire brick the bauxite is first washed to remove free silica and then calcined at a temperature of 2,500° F. Very little or no shrinkage takes place below the temperature of 2,390°, hence 2,500° is about the lowest safe temperature that may be applied.
The calcined material may be bonded with plastic fire clay, sodium silicate, or free lime, and the bricks, after drying, are burned in down-draft kilns at high temperatures, such treatment rendering them hard and tough. A 9 by 22 by 42-in. brick weighing 71⁄2 lbs. has been found to stand a crushing test of 10,000 lbs. per sq. in.
'The next article will deal with the manufacture of Nitric Acid of high acidity, making and preparing mixed acid and preparing same for shipment, with suggestions toward eliminating trouble and expense of settling the acid. It will also suggest a profitable utilization of nitre cake (acid sodium sulphate).
ELECTROLYSIS AND CORROSION.'
By ALLERTON S. CUSHMAN.
It is assumed for the purpose of this paper that by corrosion we mean the effects produced on the metals by the combined action of water and oxygen, with or without the stimulus provided by various impurities in the water or in the atmosphere. Few authorities now deny that in this sense of the word the corrosion of all metals is simply a matter of electrolysis. It is necessary, however, before proceeding with the discussion, to be quite sure that we are all accepting the same definition of electrolysis. The word was first used by Faraday to express the decomposition of compounds by the electric current, but today it is used in a wider sense, and electrolytic phenomena are recognized whenever a strip of any ordinary metal is immersed in water. There has unfortunately been a widespread impression that electrolysis, as it applies to the corrosion of metals, can take place only if electricity, or electrical circuit involved, can be traced to some definite extraneous source. Thus it has come about that engineers, metallurgists and others to whom the causes of deep corrosion and pitting of metals is a matter of anxious inqury, have wasted much valuable time, feeling about with voltmeters and galvanometers in vain efforts to locate and insulate the dangerous intruder. While it is not my present intention to combat the idea that stray, escaped currents play a contributory part in some cases of corrosion, I wish to emphatically point out that corrosion is eternally going on where no extraneous currents can be held responsible for the damage.
In order to understand exactly what is meant it will be necessary to consider briefly the modern physico-chemical explanation of electrolytic solution-tension. It is well known that when a liquid or a solid is heated, some of the molecules pass into the form of vapor or gas, and in any closed space equilibrium is established for a given temperature when the vapor exerts a certain definite pressure. As Nernst, who first gave expression to this phase of the modern theory of solution puts it:
"If, in accordance with Van't Hoff's theory, we assume that the molecules of a substance in solution exist under a definite pressure, we must ascribe to a dissolving substance in contact with a solvent, similarly a power of expansion, for here also the molecules are driven into a space in which they exist under a certain pressure. It is evident that every substance will pass into solution until the osmotic partial pressure of the molecules in the solution is equal to the solution tension of the substance."
To use a rough analogy, this is no more complicated than saying that a company of people pressing from one room into another will find themselves
'Presented at the meeting of the American Society for Testing Materials, at Atlantic City, N. J., on June 23, 1908.
in comfortable equilibrium just as soon as the expansive power of the company in the newly occupied space is about equal to that left in the originally overcrowded one. It should be understood, however, that individuals may be passing continually backwards and forwards between the rooms without essentially disturbing the equilibrium, but if we further assume that some barrier or force prevents a person having once passed into the new room from exerting back pressure the stream of new arrivals will continue, to the depletion of the company in the original room. Also precisely the same result would accrue if the individuals pressing into the second room were slowly but constantly being removed by passing down a narrow stairway and thus being removed from the scene of action. Leaving now this rough analogy, whose application, however, will soon be apparent, we may return to Nernst's conception of solution-tension. The metals probably without a single exception have the possibility of passing into solution as positive ions, that is to say, as atoms carrying relatively to their mass enormous static charges of positive electricity. Every metal in water has a solution-tension peculiar to itself, provided it is pure, but as we shall see, this property is enormously modified under most circumstances by a most remarkably small presence of certain impurities. To quote from a well known text book on physical chemistry:1
"If we dip a metal into pure water, let us see what will take place. In consequence of the solution-tension of the metal, some ions will pass into solution. When metallic atoms pass over into ions they must secure positive electricity from something. They take it from the metal itself, which thus becomes negative. The solution becomes positive, because of the positive ions that it has received. At the plane of contact of the metal and solution, there is formed the so-called electrical double layer, whose existence was much earlier recognized by Helmholtz. The positively charged ions in the solution and the negatively charged metal attract one another and a difference of potential arises. The solution-tension of the metal tends to force more ions into solution, while the electro-static attraction of the double layer is in opposition to this. Equilibruim is established when the two forces are equal. Since the ions carry such enormous charges, the number that will pass into solution before equilibrvim is established is so small that they cannot be detected by any ordinary method."
It is apparent from this, that since under the ordinary conditions of service metals suffer corrosion only by first passing into solution, the corrosion can only be prevented or inhibited, either by aiding the resistance to the entrance of more ions into solution, or by covering the surface of the metal with a waterproof coating, or by doing both these things at the same time, on the principle that a double barrier is more impregnable than a single one. If we had to deal always with chemically pure 100 per cent metals which
'Elements of Physical Chemistry. Jones, p. 449.
Wied Ann. 7, 337 (1879).