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carried out, as we have said, a number will lose less than 9 per cent. by being of experiments with results the general punched, the steel made by another firm, nature of which we have already indi- at least as eminent, loses 26 per cent., or cated. They appear to show that when nearly three times as much. Furthera plate is punched it loses strength, but more, it is stated that the effect of that when punched and annealed, or punching is to deprive the metal of all punched and rimed out to size, or power of stretching, and the consequence drilled, it gains in strength. Thus a is that it breaks with a crystalline in& in. plate which, unperforated, bore a stead of with a fine silky fracture. strain of 30.7 tons per inch, bore 31.6 Bearing these facts in mind, let us contons when punched and annealed, 31.23 sider what light they throw

on the tons when punched small and bored to peculiarities of steel. It is known that size, and 31.46 tons when drilled. With if a steel boiler plate be punched, the a 1 in. plate the figures are 28.17 tons chances are about one hundred to one for the solid plate, punched 21.26, that cracks will start from all the rivet punched and annealed 29.12, punched holes in the edges of the plate, if not small and bored to size 29.15, and from one to the other, almost before the drilled 28.43 tons; all the dies were riveting of the seam is completed. On about 20 per cent. larger in diameter the other hand, Lloyds permit steel ship than the punch. Putting these figures plates to be punched and riveted up into percentages we have for the į in. without riming or annealing, provided plate—the strength of the solid plate they are not more than in thick, and being 100—punched 93 8, punched and do not come under severe strains-garannealed 104.7, punched small and bored board strakes, sheer strakes, and deck out 103.5, drilled 104.2; for the 1 in. stringer plates must, if punched, be plate the figures are 75.4, 103.3, 103.4, annealed or rimed. Leaving ships, howand 100.9. Here, again, we have ample ever, and returning to boilers, we may corroboration of our often urged argu- say at once that no one dreams of putment that the properties of thin steel ting a steel boiler together with punched plates do not form a guide to those of holes, unless the plates are carefully thick steel plates.

annealed. On the other hand, scores of If we compare these results with iron boilers are made with punched others obtained at different times, and holes, and no cracking takes place, and by other experimenters, it will be seen the boilers are quite sound and good. that some difference exists. Thus ex- To this it will be replied that iron does periments made at Liverpool and Shef- not lose strength by being punched, and field in 1878 showed that I in. plates that for that reason it may be punched lost only about 8 per cent. by punching, with safety. It will, perhaps, be new to which nearly agrees with the figures many of our readers, but it is none the given above, while the 1 in. plates lose less true, that this is a complete mismore than 33 per cent., instead of less take. Iron boiler plates do lose in than one-fouth, as given above. Again, strength by punching. A set of experiaccording to the Board of Trade, steel ments made in 1878 on best boiler plates plates in. thick lost but 8.6 per cent. in. thick, such as are used for marine by punching, while in the experiments of boilers of moderate size, showed that while which we speak the loss was found to the solid plate had a tensile strength of reach as much as 26

per cent. We have very nearly 20 tons per square inch, the here a very important disparity, and one metal lost in strength when punched which should be cleared up. Is it to be with an open die, 22 per cent. ; when explained by differences in the quality of punched with a close die, 20 per cent.; the steel, or by peculiarities in the system when punched and rimed, 11.4 per cent.; of testing employed? So far as we can see and when punched and annealed, 4 per it depends entirely on the first condition, cent. of its original strength. A second namely, the quality of the steel; and it set of experiments on ostensibly a better should be remembered that in both class of “best best" plates as supplied to cases the steels used were ostensibly the the Admiralty showed that under similar best that could be made. We find then conditions the iron lost 18 per cent. of that while the steel made by one firm its strength by punching, and even when

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the holes were rimed the loss was 9.2 per they must operate on comparatively large cent., and when they were drilled 3 per quantities of the metal. It is very easy cent. Here we see that although the to speak, for instance, of .1 per cent. of loss is somewhat less than is the case carbon, but few persons realize what it is with steel, it is nevertheless very con- the chemist who seeks for this has to siderable. But the injury inflicted on find. 0.1 per cent. of carbon means that iron by punching does not seem to a ton of steel contains 2.24 lbs. of carbecome apparent. The metal keeps its bon, each pound of the metal will consorrows to itself. It shows no outward tain 7 grains of carbon; and as the signs, and the 80 per cent. or so of chemist operates on but a few grammes strength left in the plate is always worth of the steel at a time, it will be seen how 80 per cent. But of the 80 per cent. or minute are the quantities of carbon, sulso left in steel no one can tell the value phur, and phosphorus with which he even approximately. Why is this? All has to deal. But this would present no the explanations which have been put difficulty were it not that the analysis of forward to supply an answer will apply iron, especially for carbon, is one of the just as strongly to iron.

most troublesome known, and we feel We are told that when a steel plate is certain that many statements which now punched, a ring of hard metal is left serve to perplex investigators struggling round the hole, which being compressed to arrive at the truth would be found tends to split the plate, or prevents the erroneous if only accurate analyses were strains being equally distributed through available. Again, the testing of steel it.

plates in a machine is not a true test, Remove this hard ring with the because it specially eliminates the condirimer, or soften it by annealing, and the tions under which steel suffers most, and plate becomes as strong as ever. But is least trustworthy. Thus the strength does not all this hold good of punched of riveted steel joints should be asceriron? Is there not in its case a hard tained by putting sudden strains ring round the holes? Cannot this ring them, such as they may be supposed to be rimed with the rimer or softened away suffer when a long ship is steaming head by fire? The answer must be in the to wind in a heavy sea ; and again, tests affirmative. The only feature indicating of boiler plates ought to be made with a different condition is that iron seems to the plates hot, not cold. The inquiries be permanently injured to a small extent which have been made up to the present even by drilling, while steel is improved. are so misleading, that little or no regard The hard rings will not render an iron is paid to them; and those who use steel plate treacherous, while they make steel freely rely entirely on their own practical plates quite untrustworthy. Like causes, acquaintance with it, and care little or in a word, do not produce like effects; nothing for the figures which exist in and to complicate the case still further, such multitudes. The great safeguard a Motala plate from Sweden, did not seems to be to deal for steel only with seem to lose any strength by being firms who have already supplied what punched, plates .45 in. thick baving an has proved to be good. This is very initial strength varying between 27 and hard, perhaps, on young firms; but it is 28 tons per inch before punching, and not easy to see how it can be helped. If standing as much as 28.2 tons after only steel did not now and then play punching

those who use it false; if only it were We have little reason, then, to doubt not so susceptible of being deteriorated, that the true reason why punched steel that a change in the form of the ingot plates will not answer for constructive moulds has been known alone to suffice purposes, while iron plates will answer, to render tons of steel next to useless, has yet to be sought out, and the in- iron would cease to be made save for a quiry must take two distinct directions. few special purposes. The unsatisfactory In the first place, we must have much aspect of the steel question as a whole is more accurate analyses of steel to deal that we seem to make no progress, and with than are now available, and chemists that we know no more about it now than appear to be agreed that to make them we did five years ago.

Yol XXIV.-No. 6–34.

THE OPTICAL DYNAMOMETER.

Translated from “l'Electricien." In testing dynamo-electric machines it the shaft has been measured by a spiral is a matter of considerable importance to spring. determine the amount of work absorbed The dynamometer of M. Satchinoff by the machine alone, without the inter- presents the peculiarity of permitting vention of other factors which are capa- the reading to be taken directly while

the machine is in motion. The reading is made from graduations on the inner surface of a moving pulley, and is based on the principle of persistence of luminous impressions on the retina.

The figures 1 to 4 exhibit the plan of working of the apparatus. It consists of two pulleys, A and B, the former running loose upon the driving shaft, while B is keyed fast to it. The arms of the pulley A are attached to those of B by three spiral springs C, C, C. B is furthermore

B

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furnished with a rectangular slit R, through which the readings are made while the machine is in motion.

Under ordinary circumstances the driving belt is run on the keyed pulley B, and the shaft is then driven without any

strain on the dynamometer. When a Fig.2

test of the power is required, the belt is

run upon the pulley A, as shown in Fig. the revolutions of the machine. The 4. The shaft is then driven through the only difficulty is in measuring the tan- agency of the springs, and there regential effort

sults a certain amount of angular disDifferent devices have been employed placement of the pulleys, the amount of for this purpose. In some the difference which depends upon the effort required in tension between the belt leading to to overcome the resistance to be measthe driving pulley and the belt leading ured. The graduations on the inner from it has been measured. In others surface of the pulley A serve to measure the effort of the driving pulley to turn the displacement, and consequently the

strain, by referring to the fixed reference may be read directly in pounds or kilopoint n on the edge of the pulley B. grams.

The slit R is placed opposite to n, and This dynamometer is very simple, and

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permits n and the graduations to be capable of a great variety of applications, plainly seen while the wheels are in and it is especially serviceable in cases of rapid motion. By previous adjustment high velocity, a condition met with in all of the springs the force or resistance the dynamo-electric machines.

WEIGHT, SPECIFIC GRAVITY, RATES OF ABSORPTION AND CAPABILITIES OF STANDING HEAT OF

VARIOUS BUILDING STONES.

By HIRAM A. CUTTING, Ph. D., State Geologist Vermont. Having during the past year instituted, could at any time be compared, and if in and carried out, a series of experiments the working of a quarry there was a to ascertain, as nearly as possible, the change in gravity, or weight, that it could capabilities of the various materials used be easily detected, and thus all who in the construction of so-called fireproof choose could know whether the tests buildings to stand heat, I submit, in tabu- given would apply or not. lated form, the result of such experi I have procured sample specimens of ments, hoping they may be of use to the the most important building stones in architects, quarrymen and Insurance the United States and Canada, and, after companies of our country, and also of dressing them into as regular form as some interest to those interested in sci- possible, three by four inches, and two ence.

inches in thickness, I have taken their In connection with the capabilities of ratio of absorption, which ratio I have the various building stones to stand fire expressed in units of weight, according and water, I have taken their specific to the amount of water taken up. If 450 gravity, and weight per cubic foot, so units of stone absorbed one unit of water, that the identity of the various stones I have expressed it thus: 1+450, mean

ing that the stone weighed 450 units been unable to note any marked differwhen immersed, and 451 when taken ence in the action of heat, beyond this, from the water.

that the dry specimens became sooner To accelerate the process of absorption heated. I have, however, no doubt that I have placed the specimens in water the capacity of a stone to absorb water is under the exhausted receiver of an air against its durability, even in warm clipump.

mates, and vastly more so in the changeI find that in this way as much able and wintry climate of New England. water is absorbed in a few minutes as in It is here often frozen before any considdays of soaking. When specimens were erable part of the moisture from Autumn removed from the water, I have, before rains can be evaporated. weighing, dried their outsides with blot When the specimens were heated to ting paper. In relation to the specific 600° Fah., I have immersed them in gravity, I have not followed “Gilmore's" water, also immersing others, or the same, rule in full. He weighed the specimens if uninjured, at 800° and 900°, that is if in air, immersed them in water, and they are not spoiled at less temperatures. allowed them to remain until bubbling I find that all of these samples of buildhad ceased and then weighed them in ing stones have stood heat without damwater, after which he took them from the age up to 500°. At 600° a few are water, dried them outside with bibulous injured; but the injury in many cases paper, and weighed them again in air. commences at or near that point. When From this last weight he subtracted the cooled without immersion they appear to weight in water, dividing the dry weight the eye to be injured less, but are ready by the difference.

to crumble, and I think they are many This gave a specific gravity subject to times nearly as much impaired, and two sources of error. I have followed always somewhat injured, when water the more frequent custom of weighing produces any injury. the dry stone, using pieces of two or I would remark that my experiments three pounds in weight, and then im with granites show that there is quite a mersing them in water. After the usual range in their capabilities of standing saturation I have taken their weight in heat, a range in fact much greater than I water, subtracting it from the dry weight anticipated. With the sandstones the in air, and then dividing the dry weight difference is also marked, as is their by the difference. This gives the specific power of absorption. When exposed to gravity of the rock itself, as usually found, the heat wet, they show a marked differwhich is what we desire, and I believe as ence in the time required to heat them, it would generally be in buildings con- the saturated ones seeming to resist the structed of the given material. The heat for a time; but when equally hot specimens were previously dried by long they crumble the same as those not preexposure to a temperature not exceeding viously saturated. Their relative worth 200° Fah. To verify this I have taken can be seen by the table. The conglomspecimens from the quarries direct, and erates stand heat badly; while the limeafter weighing, have brushed them over stones and marble stand best of all (up with paraffine dissolved in naphtha, to the point where they, by continued weighing them again so as to ascertain heat, are changed to quick lime) except the exact amount of paraffine, which soapstone, and a species of artificial stone made no visible change in the stone, made under the McMurtire & Chamberother than to keep out water. I have lain patent. The indications are, from then weighed in the usual way, and thus this and other samples of artificial stone, obtained the exact specific gravity of the that it may be possible to make an artistone as in the quarry, and I find my ficial stone cheaper and better for firemethod used, as stated, to give the best proof buildings than our native quarries results, and so have adopted it.

furnish ; and we hope this possibility After this I have placed them in a may receive attention. But comments charcoal furnace, the heat of which was are useless, as the facts set forth in the shown by a standard pyrometer. In tables speak for themselves. many instances I have placed them side I give you results in tabulated form by side with dry specimens, but have on following pages:

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