MR. J. SCOTT RUSSELL'S MARINE SALINOMETER. [From Description by Mr. Russell read before the Royal Scottish Society of Arts, and published inthe last Part of their Transactions. The Society afterwards awarded their Honorary Silver Medal to Mr. Russell for his communication.] VERY early in the history of steam navigation, the inconvenience of raising steam from salt water was experienced. When the Comet descended below Port Glasgow in 1812, the boiler was found to boil over, or prime, as it is technically called by engineers, when part of the water is forced up so violently, along with the steam, as to pass over into the cylinder of the engine-a circumstance 'always detrimental, and sometimes destructive to the engines. This arises from the thickening of the water, its density being increased by the retention of the solid substances which compose sea-water, and which remain and accumulate in the boiler, while the fresh portion of the water is passing off in the shape of steam. This process of accumulation of solid matter in the marine boiler is by no means slow. The whole of the water which a marine boiler usually contains is evaporated in three or four hours, leaving the solid substances in the cubic content of boiler behind it, and being replaced by salt water, with an equal quantity of depositary matter, accumulating as rapidly as before; and since it is known the solid matter amounts to as much as of the whole mass of water, it would follow, if the process of ebullition could continue so long as 150 hours, there would be deposited in the boiler a quantity of solid matter equal to the number of tons of water in the whole content of the boiler. Long, however, before this degree of solidification can take place, evils of a different description intervene to impair and put an end to the functions of the boiler. The solid constituents of salt water which are left behind do not diffuse themselves uniformly over the whole liquid mass, so as to constitute a homogeneous brine; on the contrary, the new supplies of sea-water, as they enter the boiler, remain secluded from the former more saturated brine, rise by their less specific gravity into an upper stratum, while the denser brine forms a bed in the lower part of the boiler, and surrounds the fire-box and heater-flues occupying the water-spaces and legs, which are usually at a high temperature, and which, in double-tiered boilers, are generally the most intensely heated. The intense heat of the metal expels the water from the brine in contact with it most rapidly in the hottest places, and salt is deposited on the hottest parts of the furnaces and flues, extending rapidly to those less heated, and so not only diminishing the evaporative power of the boiler, but injuring its substance, and endangering its existence. The remedy for these evils was very early invented. But I have not been able to discover the inventor of the cleans 66 ing process commonly called "blowing down," or 'blowing off." It is almost universal, and is performed in the following way: There is forced into the boiler, at each stroke, rather more water than is required for the supply of steam, so that the boiler becomes too full. Openings are then suddenly made at the bottom of the boiler, and the brine at the bottom being violently ejected, carries with it any solid substances that may have accumulated near the bottom-the boiler is thus cleansed; and before the water has got too low, the openings are again closed, and the boiler continues to be fed as formerly. Another remedy, pretty generally adopted, is the brine-pump, by which, for every portion of water supplied to the boiler, about one-fourth part of that quantity of brine is withdrawn from it. This pro cess does not so thoroughly carry off all the impurities as the former; but it is attended with a saving of fuel by a contrivance for giving to the feed-water entering the boiler a portion of the heat of the discharged brine. The recent introduction of this process is due to Messrs. Maudslay and Field of London. In whatever way the saturation of the water with solid matter may be remedied, it is essential to the accomplishment of this object, that some simple apparatus should be contrived for the purpose of showing when the cleansing process is re MR. J. SCOTT RUSSELL'S MARINE SALINOMETER. quired, and whether it is successfully applied. If this be not obtained, the usual consequence of acting on wrong data are sure to follow. A contrivance was patented, which was thought promising, but was found liable to be mechanically out of order when most wanted; a ball of greater specific gravity than salt water was connected with an external index, by which there was indicated on the outside the fact of the brine becoming sufficiently saturated to float this ball. Another was to place in the glass gauge of the boiler a glass hydrometer bead, which would float when the brine became saturated to a given point, and fall to the bottom in the ordinary state of the boiler. But this fails entirely of accuracy, although very elegant; for the brine of which we wish to indicate the density is in the lower stratum, not the upper one, where the usual glass gauge is placed, and irretrievable mischief might be done before the indicator would show any change. I have lately employed, in some large ships destined for transatlantic voyages, a species of brine gauge, or index of saturation, which is found to possess every advantage, and which I therefore desire to communicate to the public through this Society. The accompanying figures are such as may enable any engineer to construct them for himself. The details of the arrangement of the apparatus were made under the direction of Mr. James Laurie, formerly one of my assistants; and he also has obliged me by writing out the annexed description of the operation of using the index. The principle I have used is the wellknown law" that the heights of equiponderent columns of liquids vary inversely as the densities of those liquids." If I take open glass tubes bent in the form of the letter U, and pour one fluid into one of the sides, and another fluid into the opposite side (taking care to use the heavier liquid before the other): the one being mercury, and the other water, they will stand at the height of 1 inch and 13 inches respectively. If I use alcohol and water they will stand at the height of 10 inches and 8 inches respectively, the height of the one fluid being always greater than that of the other, in the pro 35 portion in which its weight, density, or specific gravity is less. In like manner, fresh water and salt water will stand at heights of 40 and 41 inches, showing a difference of 1 inch. The use which I make of this principle is as follows:-I reckon the best scale of saltness of a boiler to be that which takes the common sea-water as a standard. Sea-water contains of saline matter. When the water has been evaporated, so as to leave only half the quantity of distilled water to the same quantity of saline matter, I call that two degrees of salt, or brine of the strength of two, and such brine would show the columns 40 and 42, or double the saltness of sea-water, indicated by a difference of 2 inches. A farther saturation would be indicated by a difference of 3, 4, 5, and 6 inches beween the columns, and so indicate 3, 4, 5, 6, and any farther degrees of saltness-a range which may be made to any degree of minuteness by the subdivision of the scale of inches. This scale is that which appears to me most simply applicable here-and it is that which I adopt for marine boilers. The mechanical apparatus which I have employed to give this indication is perfectly simple, and has the advantage of being such as the engineer already perfectly understands. To the marine boiler I apply two water-gauges of glass, instead of one as at present used; they both serve the purpose of the present glass gauges, and the pair would be valuable for this, if for no other reason, that there would always be a duplicate when one is broken, an accident not unfrequent. To these gauges I simply attach small copper pipes, so that one of them may be placed in communication only with the salt brine in the lower part of the boiler, and the other with the feed-water which is entering the boiler; the one then holds a column of brine, and the other of pure sea-water, and each inch of difference shows the degree of saturation. Without the use of any attached scale, the engineer, by a little practice, comes to know in his particular vessel what difference in inches can be admitted without danger, and at what difference of height it is imperative to blow off. But it is convenient to have an attached scale. It may be satisfactory to state, that the practical range of scale in an ordinary boiler in the ordinary working, is 6 to 10 inches, a difference sufficiently great to be easily observed. The rule of working them is nearly this:-Continue the operation of blowing off until, if possible, the difference of the columns is less than an inch; it will be unnecessary to blow off again until the difference is at least 6 inches. As a practical rule, I find that it is necessary to blow off when the brine at the bottom has about three degrees of saltness. But this will vary exceedingly, according as the construction of the boilers is more or less judicious. When the heat is greatest in the lowest portion of the boiler, and the flues return above, they will be most liable to salt, and require the most frequent cleansing. The following is Mr. Laurie's description of the instrument. The drawings give the details of the apparatus.-J.S.R. Description. The fact that the specific gravity of salt-water is greater than that of fresh, and that it increases with the degree of saturation, is what the operation of this instrument depends on; by its means two columns of water, the one feed and the other brine, are poised against each other, so as that any difference of weight betwixt these columns immediately becomes apparent by the lighter of the two requiring an accession in quantity to resist the upward pressure to which both columns are subjected. This is accomplished by having two common glass-gauge tubes close together, each of which is connected with a separate tube; that inside the boiler descends to the level of the water, the specific gravity of which is to be measured, and having either or both of these tubes so connected with the feedpipe of the boiler, that by opening a cock one of the pipes will be filled with feedwater, while the other remains filled with brine, which cock being shut, the tubes remain so filled: but inasmuch as feedwater is of less specific gravity than brine, it will be forced up and stand in the glass tube at a higher level than the brine, which difference of levels increases with the saturation-and hence the index to judge of the saltness. A, B, are two glass gauge-tubes; C, one of the tubes forming the connexion betwixt one of these glass gauge-tubes and a tube D, which descends inside of the boiler; E, the tube forming the connexion betwixt the upper ends of these tubes and the inside of the boiler; F, G, two cocks so made, as shown in the engravings, that by their means each of the tubes inside of the boiler may be shut off from the glass tubes, and also may be connected with the tube H, leading from the feed-pipe of the boiler; I, a cock affording the means of shutting off the tube E from the glass tubes with the tube K, leading to the bilge of the vessel; each of these cocks has a handle, and when the instrument is indicating, the three handles hang perpendicularly downwards. Sections of the cock at M N and OP, are given separately. To bring the instrument into operation, the three handles ner, cleanses and fills B and its tube inside the boiler with brine; finally, bring the handle of the top-cock into its original position, and put either of the lower handles horizontal, which forming a connexion of the feed-pipe with one of the tubes inside of the boiler, fills that tube with feed-water; thus there are in the two tubes inside of the boiler two columns of water of different specific gravities, the one being brine, the specific gravity of which is to be measured, and the other feed-water, the specific gravity of which is pretty nearly constant, so long as the temperature of condensation is the same, and does not vary much let the temperature of condensation be what it may; but, inasmuch as these columns of water are of different specific gravities, the pressure on the bottoms of them will force the lighter up the glass tube, until such a quantity of brine has followed it as makes it of equal weight with the other; and hence, in the two glass tubes, the water stands at different heights, the HAM'S INSTRUMENT FOR ASCERTAINING THE SPECIFIC GRAVITY OF FLUIDS. 37 magnitude of which difference becomes known by means of the scale fixed betwixt the glass tubes, and therefore also the degree of saturation of the brine. The use of this instrument, which might be called a Salinometer, is not confined to this one object, for it answers thoroughly all the purposes of the common glass gauge, the position of the surface of water in the boiler being midway betwixt the surfaces of water in the tubes. When either or both of the glass tubes is broken, put the handles in the position, and nothing can escape from the boiler. 200 190 180 I DESCRIPTION OF AN INSTRUMENT FOR AS CERTAINING THE SPECIFIC GRAVITY OF 170 Sir, I beg to forward, for insertion in your highly popular publication, the drawing of an apparatus for readily ascertaining the specific gravity of fluids, which I devised some months since, and find extremely useful in practice. By having the scale minutely divided, or adapting to it a vernier, it is susceptible of a high degree of accuracy, and for all ordinary fluids, is infinitely superior to the gravity bottle and balance, and in many instances preferable to the common hydrometers, especially in commercial transactions, where rapidity and accuracy are essential points. A and B are two glass tubes, from to ths of an inch bore, and of any convenient length; about 2 feet will be found sufficient for usual purposes; Ca connecting brass tube and stop-cock; D and E two glasses, one for distilled water, the other for the liquid whose specific gravity is required; F and G, two milled-headed screws, carrying each a stand for one of the glasses; H, a bracket with two nuts, for supporting the screws and stands, F G; II, the scale, divided into 200, or 2000 equal parts, or degrees. The mode of using it is simply this: Pour distilled water into one of the glasses, and the liquid to be tried into the other, both at 60°, or any moderat: 30 I 20 H uniform temperature. Exhaust the air in the tubes either by means of a syringe, or the mouth being applied at the stop-cock, C-until the lightest fluid is nearly at the top of one of the tubes; then bring the surfaces of the two fluids, in the glasses E and E, on a level with the marks, a a, on the tubes, by means of the screws, raising or lowering the stands as required; the heights of the fluids in their respective tubes will immediately give their relative gravities, convertible into water at 1000, by simple proportion. I am, Sir, Norwich, Jan. 9, 1844. F. HAM. AND ON THE MACHINES FOR RAISING LOWERING MINERS, AND ON THE USE OF THE IRON WIRE ROPE, IN THE MINING DISTRICT OF THE HARTZ. BY JOHN TAYLOR, ESQ., F.R.S., ETC. As some things came under my notice during my recent visit to the mining district of the Hartz, which may be interesting to the Members of the Polytechnic Society, I will endeavour to communicate the result of some of my observations and inquiries. In the first place, I was desirous of knowing whether the machines for raising and lowering the men, continued to answer their purpose satisfactorily, and whether, as the best evidence of this being so, they were extending in use. I found that they were spoken of by all the principal officers of the mines, in terms of great commendation. heard of no adverse circumstances that had occurred in using them, and I understood that they were now applied in every situation that afforded facilities for erecting them. I I saw one in action which I need not describe, as you have a perfect account of the construction, in the reports of the society; but it appeared to me to be inferior to what has been executed at Tresavean, the brackets or platforms on which the men stand were small, and the iron loops for holding by were not, in my opinion, very conveniently arranged. The stroke of the rods, also, was much shorter than that proposed to be adopted in Loam's machine; still the arrangement seemed to be perfectly effective, and the ease with which the men seemed to step from one rod to the other, and were thus carried up or down, was very pleasing to witness, and had rather a striking effect in its appearance. In one of these machines, which is carried to a great depth, it has been attempted to strengthen the timber rods, or to give them additional security, by attaching to them a wire rope. I doubt much whether this be a good way of accomplishing this purpose, and I had much conversation with our friend Mr. Jordan, the Machinen Inspector, on the subject. It is found that the wire rope when extended and stretched in connexion with the rod, being in a state of rest and exposed to the wet and to the heated air of the mines, soon oxidizes, and may thus become considerably weakened, in a manner that may easily escape observation, and thus a delusive appearance of strength may be relied upon. As the wire ropes which are in universal use now in the Hartz mines, for drawing up the ores and waste, are not subject to oxidation in any degree that sensibly impairs their strength, this defect in another application of them was not foreseen, and the difference must, I conceive, be accounted for by the fixed state in the one case, and the constant motion in the other. I suggested to Mr. Jordan that the oxidation might probably be prevented by a process now much used in France, but which I have not heard much of in England, and that is coating iron with zink, in the same way as it is covered with tin in the manufacture of tin plates. This is termed galvanizing the iron, and I know from the best authority, is very successful in protecting it from rust. It is commonly applied to wire work that is to be exposed to the weather; such as trellis work for gardens, &c., and is performed after the wire is woven into the forms required, and at a very cheap rate. It unites or solders the joints or crossings, gives the whole a very pleasing appearance, and is effectual in preserving it for a great length of time. For wire ropes that are extended in a rigid state, such for instance as standing rigging, it might probably be advantageously adopted, though it probably might not answer for those which are employed to wind on whim cages and to run over pulleys, and in which cases indeed it does not appear to be required. The members of the Polytechnic Society are aware that the principle upon which the machines for raising men from the mines have been constructed, was suggested almost contemporaneously in Germany and Cornwall, without any communication between the inventors at either place, and it is one of numerous cases that might be adduced, where the merit of invention has been due to more parties than one. |