March 3, 1916. THE COLLIERY GUARDIAN 409 between two more or less hard surfaces. Fineness is to a large extent determined by the intensity of the blow, and hence different degrees of reduction may be had by simply varying the speed of the machine, without much regard being paid to the other parts. .There are several types of the Jeffrey swing hammer pulveriser. Type A is a general purpose machine. Material fed from above falls down on a sloping breaker plate where it is engaged by the rapidly revolving hammers. The partially reduced material immediately passes over the cage of screen bars, where all that fe Sufficiently fine will pass through, while the residue is carried around the machine for a second operation. The 'Op breaker plate materially assists in reducing this oversize material. Type B (fig. 4) is heavier and better built than type A. These machines are fed directly on top of the hammers, the feeding point being much higher. For reducing ores and similar substances, the hammers are regularly made of manganese steel. For special work these hammers may be made of tool steel, and for other classes of work a high carbon steel gives excellent results. All sizes of type B machines are provided with an adjustable breaker plate which may be set up close to the revolving hammers. The breaker plate is protected from wear by a heavy chilled-face corrugated liner bolted to its face. material fed to it from the section above. It is usual to use four sections of sampling chutes, so that but one-sixteenth of the original material is delivered at the bottom of the chutes, but this, material will be a true sample of the whole lot. The construction and size of these hoppers and sampling ohutes vary with different conditions. Yet another machine, type I) (fig. 6) is designed for fine grinding of limestone, shale, etc. This machine, which may be driven by a direct connected motor of proper power and speed, engages the material on the up stroke of the hammers. Three breaker plates are arranged at intervals about the upper portion of the grinding case in such a way that the material is violently tossed back and forth between the rapidly revolving hammers and the anvil faces of the breaker plates. Consequently the reduction is mostly by impact, and the material being the same, the degree of reduction varies with the peripheral speed of the hammers. An automatic feeder suitable for regulating the flow of material from a storage bin is supplied with each machine. This feeder is so enclosed and protected by a steel hopper that any over- flow caused by the operation of the feeder valve is dropped directly into the machine, and hence there is no material dribbling over the sides of the feeder. The length of the stroke, the position of the valve plate and COKE OVEN MANAGERS’ASSOCIATION. WAR DIFFICULTIES. At a meeting of the Coke Oven Managers’ Association held at the Applied Science Department of Sheffield University on Saturday last, February 26, when Mr. George Chrisp presided over a fair attendance of members, Mr. G. Stanley Cooper, B.Sc., F.C.S. (of the Yorkshire Coking and Chemical Company, Castleford), read a paper on “ Some Difficulties Due to the War : and Possibilities of Future Development.” The President, in introducing Mr. Cooper, explained that he had very kindly consented to give this-paper a month earlier than originally arranged for, to fill a breach in the association’s syllabus, and therefore appealed for consideration, as he felt that in the short- time at his disposal he had scarcely been able to do either the subject or himself justice. Mr. Cooper then read his paper, of which the follow- ing is an extract :—• Some Difficulties Due to the War : and Possibilities of Future Development. The original suggestion by the council with regard to this paper was that it should deal with methods of using arsenical sulphuric acid in the manufacture of sulphate of ammonia, PIVOTED! ^BUCKET/ CRANK DISCS iWf Hl ■■■iW Fig. 3.—Elevation of Plant with Oscillating Feeder. Fig. 4.—Type B Pulveriser with Plate Feeder. Fig. 5.—Sampler. The equipment furnished with a type B pulveriser depends in a great measure on the use to which it is to bo put. When material is fed from a belt conveyor or elevator, it is usually sufficient to build a suitable steel hopper on top of the standard machine. In most cases it is preferable to use a reciprocating plate feeder for regulating the .amount of material to be fed to the machine. The makers have arranged a drive for this feeder directly off of the pulveriser shaft, so that the machine will be self-contained. By the use of this feeder the material may be taken directly from storage blns and delivered to machine at any required rate, for they are adjustable, both as to length of stroke and amount of throat opening. Another machine is built for laboratory use in reducing many materials to a fine uniform product. For sampling coal and kindred uses, the arrangement shown in fig. 5 is recommended. It: consists of a hopper large enough to hold a batch in which the material is held by a sliding valve at the bottom. This’ discharges into a second hopper which leaves an opening into which material may be shovelled without regard to the upper hopper. As the ground material passes out of the pulveriser it is caught in a sampling chute below. The first section of this chute-rejects half of the material, the second section is placed at right angles to the first, and rejects half the material passing through the first section, and so on, each section rejecting half of the ".4it 1 Re Fig. 6.—Swing-Hammer Pulveriser, Tyre D. the throat opening are each adjustable through wide enough limits to -regulate -the flow of any material within the capacity of the machine. In a few cases where a feeder is unnecessary, it can be -replaced by a plain steel hopper. It may be mentioned that the solo agents for the •Jeffrey Company in this country are Messrs. Hugh Wood and Company, of Newcastle-on-Tyne. South Russian Coal and Coke Production.—According to the preliminary returns of the South Russian Mine Owners’ Con- gress, there has -been an appreciable decline in the production of coal in the Donetz basin in the month of December 1915. The quantity extracted amounted to 116,000,000 poods, against 128,000,000 poods in the preceding November, and 120,000,000 poods in December 1914. But the production of anthracite, which amounted to 30,000,000 poods, showed a slight increase. The total coal production for the whole of the year was as follows :—Common coal, 1,317,700,000 poods, against 1,371,500,000 poods in 1914. Anthracite made 306,000,000 poods, or a reduction on the year of 6,000,000 poods. The combined total amounted to 1,624,000,000 poods, or 59,000,000 poods less than in 1914. The production of coke in the Donetz basin amounted to 251,000,000 poods, a reduc- tion of 27,000,000 poods. The average number of workmen per month engaged at the collieries was 180,000-, against 185,000 in 1914. but I felt that I could not make a satisfactory paper on this topic alone. Difficulties there have been in many directions, and I propose to deal only with some of those associated with the operation of by-product coke ovens, and not with 'the constructional side. Arsenical B.O.V. is being largely sup- plied now to sulphate makers; and although the amount of arsenic does not generally exceed a maximum of 0-1 to 0-2 per cent., the effect is very marked on the colour of the salt. I am not able to ascertain if arsenical sulphate has any serious detrimental biological effect when used as a manure, but I do believe that much unnecessary fuss is made of the arsenic question. Eliminating Arsenic from Sulphuric Acid. Many methods of removing arsenic from B.O.V. have been tried, with varying degrees of success, but the only method which offers any inducement to coke oven people is the preci- pitation of the arsenic as sulphide by means of sulphuretted hydrogen. This method also removes other impurities, such as lead, cadmium, etc. We have on coke oven plants practi- cally an unlimited supply of sulphuretted hydrogen, and this can be employed for the direct precipitation of arsenic. On a strong acid, however, the action is to produce sulphur, which is difficult to separate, and ultimately finds its way into the sulphate of ammonia. On many direct recovery plants it is a practice to allow a little tar to pass forward into the saturator. The arsenic is precipitated as sulphide, and the precipitate is collected by the tar, and retained as a scum on the surface of the bath. The acid in store can be treated in a similar manner, bear- ing in mind, of course, that its strength. must not be excessive. A good strong mother liquor, containing about 25 per cent, of free acid, and unsaturated with sulphate, can be fairly satisfactorily treated by H2S. Where an ammonia still is in use the effluent gases can -be utilised to some extent, as they are rich in H2S; and this method has the additional advantage that all the ammonia is recovered. The mother liquor must be in an enclosed vessel, provided with a gas inlet and outlet, and a sufficient quantity of thin tar should be added to form a layer about j in. in depth. It is also desirable to provide some means of running off the tar periodically. The efficiency of the method is shown by the results of some experiments kindly carried out for me by Mr. G. E. Foxwell, of Sheffield. The tests were made on a saturated solution of sulphate of ammonia to which had been added 10-9 per cent, of sulphuric acid, the acid being of 142 degs. Twaddell, and containing 0-2 per cent, of arsenic. The solution of sulphate of ammonia therefore contained in every 100 grammes 0-028 of arsenic. A portion of the solution was taken and covered with a layer of tar about Tjin., and H2S was passed through for a considerable time. The tar was then separated, and the arsenic estimated in both the liquor and the tar. The total sulphide equivalent of the arsenic taken was 0-036. In the tar was found 0-028, and in the liquor 0-003, there being a loss of 0-005 unaccounted for. This shows that the arsenic was reduced to about 8-5 per cent, of the original amount. Substitution of Nitre Cake. The Ministry of Munitions have issued a circular con- cerning the substitution of sulphuric acid by nitre cake in the manufacture of -sulphate of ammonia. This suggestion is not new, bu-t the Government tackles it from the wrong end first. The proposal means that the sulphate produced by this method will contain 15-4 per cent, of sulphate of soda, thus reducing the ammonia content down to -about 18 per I