At the regular weekly meeting of the Polytechnic a.s.sociation of the American Inst.i.tute, held on Thursday evening, the 25th ult., the subject of boiler clothing was discussed at some length, but without any decisive conclusion being arrived at respecting the most serviceable and economical material for that purpose. It appeared from the testimony adduced, that though there is a variety of substances in use, even those which are practically acknowledged as being the most efficient are far from coming up to the required standard of utility, and are characterized by defects which are at once forced upon us by a little close examination. Felt is an admirable non-conductor of heat, but owing to its combustible nature it is quite unreliable when subject to the heat of a high pressure of steam. A large fragment of this material which had been taken off the boiler of a North River steamboat was exhibited at the meeting, scorched and charred as if it had been exposed to the direct action of fire. For these reasons felt covering is, generally speaking, confined to boilers in which a comparatively low pressure of steam is maintained. But even under the most favorable circ.u.mstances of actual wear its durability is limited to a short period.

Powdered charcoal possesses the elements of efficiency as a non-conductor in an eminent degree; but its susceptibility of taking fire militates strongly against its adoption as a boiler covering.

Besides the materials above mentioned, there are some which come under the denomination of cements; but the use of such is somewhat at variance with what a dull world would call "facts." Employing them as a clothing for a vessel in which it is necessary to retain heat is certainly the wrong way of doing a light thing, if the evidence of distinguished experimenters be worth anything.

The researches of most well-informed physical philosophers go to prove that the conducting properties of bodies are augmented by cohesion, and that heat is conveyed profusely and energetically through all solid and ponderable substances. Thus gold, silver, and others of the most solid metals are the best conductors. Next to the pure metals in conducting powers are rocks, flints, porcelain, earthenware, and the denser liquids as the solutions of the acids and alkalies. As a further evidence to prove that the pa.s.sage of heat through all substances is increased by cohesion, even some of those which are known to be among the best conductors are deprived of this property by a division or disintegration of their particles. Pure silica in the state of hard, rock crystal is a better conductor than bis.m.u.th or lead; but if the rock crystal be pulverized, the diffusion of heat through its powder is very slow and feeble. Heat is conducted swiftly and copiously through transparent rock salt, but pulverization converts the solid ma.s.s into a good non-conductor. Caloric has for the same reason a stronger affinity for pure metals than for their oxides.

Again, wood is known to be a better non-conductor when reduced to shavings or sawdust than when in the solid state. It is probably on this account that trees are protected by bark, which is not nearly so dense and hard a body as the wood. Wool, silk, and cotton are much diminished in conducting qualities when spun and woven, for the reason that their fibers are brought closer together.

Count Rumford discovered that hot water, at a given temperature, when placed in a vessel jacketed with a clothing of twisted silk, and plunged into a freezing mixture, cooled down to 185 Fah. in 917 seconds. But when the same vessel was clothed with an equal thickness of raw silk, water at the same heat and under the same process required 1,264 seconds before it reached the same decrease of temperature. It was also found by Sir Humphry Davy that even metals became non-conductors when their cohesion was destroyed by reducing them to the gaseous state.

It is now generally admitted that, heat being motion, anything, which, by the cohesion of particles, preserves the continuity of the molecular chain along which the motion is conveyed, must augment calorific transmission. On the other hand, when there is a division or disintegration of atoms, such as exists in sawdust, powdered charcoal, furs, and felt, the particles composing such bodies are separated from each other by s.p.a.ces of air, which the instructed among us well know are good non-conductors of heat. The motion has, therefore, to pa.s.s from each particle of matter to the air, and again from the air to the particle adjacent to it. Hence, it will be readily seen, that in substances composed of separate or divided particles, the thermal bridge, so to speak, is broken, and the pa.s.sage of heat is obstructed by innumerable barriers of confined air. The correctness of these a.s.sumptions has been so abundantly proved by experimental demonstrations, that every mind that is tolerably informed on the subject must be relieved of every shade of doubt respecting the greatly superior non-conducting powers which bodies consisting of separate atoms possess over those of a solid concrete nature.

The next matter of interest connected with the subject under notice is its relation to the philosophy of radiation. It has long been known that the emission of heat from a polished metallic surface is very slight, but from a surface of porcelain, paper, or charcoal, heat is discharged profusely. Even many of the best non-conductors are powerful radiators, and throw off heat with a repellent energy difficult to conceive.

"If two equal b.a.l.l.s of thin, bright silver," says Sir John Leslie, "one of them entirely uncovered and the other sheathed in a case of cambric, be filled with water slightly warmed and then suspended in a close room, the former will lose only eleven parts in the same time that the latter will dissipate twenty parts." The superior heat-retaining capacity which a clean tin kettle possesses over one that has been allowed to collect smoke and soot, lies within the compa.s.s of the most ordinary observation.

The experiments of the eminent philosopher just mentioned furnish a variety of suggestions on the radiation from heated surfaces. He found that, while the radiating power of clean lead was only 19, it rose to 45 when tarnished by oxidation, that the radiating power of plumbago was 75, and that of red lead 80. He also discovered that, while the radiating power of gold, silver, and polished tin was only 12, that of paper was 98, and lamp black no less than 100. He further says: "A silver pot will emit scarcely half as much heat as one of porcelain. The addition of a flannel, though indeed a slow conductor, far from checking the dissipation of heat, has directly a contrary tendency, for it presents to the atmosphere a surface of much greater propulsive energy, which would require a thickness of no less than three folds to counterbalance."

It is safe to infer from this a.n.a.logy that the felt covering of boilers should not only be of considerable thickness, but should be protected by an external jacketing of some sort; for, though felt is a good non-conductor, it is a powerful absorber and radiator, more especially when it has been allowed to contract soot and dust.

Various experiments have lead to the general conclusion that the power of absorption is always in the same proportion as the power of radiation. It must be so. Were any substance a powerful radiator and at the same time a bad absorber, it would necessarily radiate faster than it would absorb, and its reduction of temperature would continue without limit. It has, furthermore, been proved that the absorptive property of substances increases as their reflecting qualities diminish. Hence, the radiating power of a surface is inversely as its reflecting power. It is for this reason that the polished metallic sheathing on the cylinders of locomotive engines, and on the boilers of steam fire engines, is not only ornamental but essentially useful. Decisive tests have also established the fact that radiation is effected more or less by color.

"A black porcelain tea pot," observes Dr. Lardner, "is the worst conceivable material for that vessel, for both its material and color are good radiators of heat, and the liquid contained in it cools with the greatest possible rapidity; a polished silver or bra.s.s tea urn is much better adapted to retain the heat of the water than one of a dull brown, such as is most commonly used."

A few facts like those above stated afford more decisive information regarding the nature of heat than columns of theory or speculation. Yet it is rather strange that when so many learned and reliable men have, experimented so much and commented with such persuasiveness upon the subtile agency of heat and the vast amount of waste that must accrue by injudicious management, comparatively few have availed themselves of the united labors of these indefatigable pyrologists; manufacturing owners and corporations still persisting in having their steam boilers painted black or dull red and leaving them exposed to the atmosphere. Some persons, who pa.s.s themselves off very satisfactorily as clever engineers, affect a contempt for the higher branches of science, and a.s.sert, in a very positive and self-sufficient manner that experiments made in a study or laboratory are on too trifling and small a scale to be practically relied upon; that a tin kettle or a saucepan is a very different thing to the boiler of a steam engine.

This may be so in one sense, but the same chemical forces which operate upon the one will be just as active in a proportionate degree in their action upon the other. It was said by Aristotle that the laws of the universe are best observed in the most insignificant objects; for the same physical causes which hold together the stupendous frame of the universe may be recognized even in a drop of rain. The same observation may be applied to the laws of heat in all their ramifications; for, after all, our experiments are, in many instances but defective copies of what is continually going on in the great workshop of nature.

It would be needless to insist on the wasteful and destructive effects produced by the exposure of boiler surfaces to the open atmosphere.

Such a practice can be neither supported by experience nor justified by a.n.a.logy; and it is to be hoped that it may before long be consigned to the limbo of antiquated absurdities and be satisfactorily forgotten.

Seeing that it cannot with any show of reason be affirmed that the boiler covering materials in present use possess the requirements necessary to recommend them; the question arises as to what is the best means of achieving the object required. This is an inquiry which it is the office of time alone to answer. As the problem is obviously one of primary importance, and well worthy of the attention of inventors, it is hazarding nothing to predict its satisfactory solution at no distant date.

The plain truth is, boilers have of late become gigantic foes to human life. Explosions have increased, are increasing, and should be diminished; and they are, in many instances, caused by boilers being strained and weakened by sudden contraction from having their surfaces exposed when the fire has been withdrawn from them. Boilers are also materially injured by the excessive furnace heat which it is necessary to maintain to compensate for the large amount of caloric which is dissipated from their surfaces, not only by radiation but from absorption by the surrounding atmosphere.

As the views here laid down are drawn exclusively from the region of fact and experiment, it is to be hoped that an enlightened sense of self-interest may prompt those whom the subject may concern, to give it that special attention which its importance demands.

Attachment of Saws to Swing-Frames.

To insure the efficiency of mill-saws, it is highly important to have them firmly secured in the frames by which they are reciprocated.

Swing-frames for carrying saws are ordinarily of wrought iron or steel, and made up of several pieces mortised and tenoned together in the form of a rectangular frame or parallelogram, of which the longest sides are termed verticals and the shortest crossheads or crossrails. In the case of deal frames, the swing frame differs somewhat from that of a timber frame, in having two extra verticals, which separate it into two equal divisions. These are necessary in order that two deals may be operated upon simultaneously, each division being devoted to a separate deal, and likewise to enable the connecting-rod which works the frame to pa.s.s up the center and oscillate on a pin near the top, thereby avoiding the deep excavations and costly foundations required where the rod is engaged with the pin at the bottom. The rack that advances the deals to the saws pa.s.ses through a "bow" in the connecting-rod and the middle of the frame, the deals are placed on either side of it, on rollers purposely provided. In sawing hard deals, the saws require to be sharpened about every tenth run or journey, and every twentieth for soft. Fifty runs, or one hundred deals, are reckoned an average day's work; this is inclusive of the time required for changing the saws, returning the rack for another run, and other exigencies. For attachment to swing-frames the saws have buckles riveted to them; these are by various modes connected to the crossheads. Each top buckle is pa.s.sed through the crosshead and is pierced with a mortise for the reception of a thin steel wedge or key, by whose agency the blade is strained and tightened. The edge of the crosshead upon which the keys bed is steeled to lessen the wear invariably ensuing from frequently driving up the keys. The distances between the blades are adjusted by interposing strips of wood, or packing pieces, as they are termed, of equal thickness with the required boards or leaves; the whole is then pressed together and held in position by packing screws. The saws themselves are subsequently tightened by forcing home the keys until a certain amount of tension has been attained, this is ascertained only by the peculiar sound which emanates from the blade on being drawn considerably tight and tense. Great experience is required to accustom the ear to the correct intonation, as in general the tensile strain on the saws approximates so closely to the breaking point that one or two extra taps on the keys are quite sufficient to rupture them.

Mr. Brunel, in the government saw-mills at Woolwich, adopted a method of hanging saws by means of a weighted lever, like a Roman steelyard.

A cross-shaft affixed above the saws to the cornice of the main frame carried a lever, weighted at one end and provided with a hook or shackle at the other for engagement with the saw buckle. In using this apparatus the blades were strained one at a time by linking the lever to the buckle and then adjusting the movable weight until the desired tension was acquired, after which the key was inserted into the mortise and the lever released. This arrangement is not now in common use on account of the trouble attending its employment, and at present the saws are merely strained by hammering up the keys. The saw blades had usually a tensile strain of upwards of one tun per inch of breadth of blade. It is to be further observed that the cutting edges of the saws are not quite perpendicular, but have a little lead, or their upper ends overhang the lower about three eighths of an inch or one half of an inch, according to the nature of the material to be sawn. The object of this is that the saws may be withdrawn from the cuts in the ascending or back stroke, and allow the sawdust free escape. The eccentric actuating the mechanism for advancing the timber to the saws is generally set in such a manner that the feed commences just at the moment when the frame has attained half its ascending stroke, and continues until the entire stroke has been completed. By this regulation the saws are not liable to be suddenly choked, but come smoothly and softly into their work.--_Worssam's Mechanical Saws_.

PATENT DECISION.

_In the matter of the application of William N. Bartholomew, a.s.signor to J. Reckendorfer, for letters patent for a design for Rubber Eraser_--Letters patent for designs have increased in importance within the past few years. Formerly but few were granted, now many are issued.

To this day they have made so little figure in litigation that but three reported cases are known in which design patents have come into controversy. With their increase, questions have arisen concerning their scope and character, which have given rise to dispute and to inquiry as to the correctness of the current practice of the office in this branch of invention. While on the one hand, it is insisted that the practice has always been uniform, and is therefore now fixed and definite; on the other, it is a.s.serted, that there has never been, and is not now, any well-defined or uniform practice, either in the granting or refusal of design patents.

The act of 1836 made no provision for the patenting of designs. The earliest legislation upon this subject is found in the act of August 29, 1842, section 3; and the only legislation upon the subject is found in this section and in section 11, of the act of March 2, 1861. The definition of the subject matter, or, in other words, of a "design," is the same in both acts. It is is follows:

"That any citizen, etc., who, by his, her, or their own industry, genius, efforts, and expense, may have invented or produced any new and original design for a manufacture, whether of metal or other material or materials, any original design for a bust, statue, bas-relief, or composition in alto or ba.s.so-relievo, or any new and original impression being formed in marble or other material, or any new and useful pattern, or print, or picture, to be either worked into or worked on, or printed, or painted, or cast, or otherwise fixed on any article of manufacture, or any new and original shape or configuration of any article of manufacture not known or used by others, etc."

This definition embraces five particulars.

1. A new and original design for a manufacture.

2. An original design for a bust, statue, etc.

3. A new and original impression or ornament to be placed on any article of manufacture.

4. A new and useful pattern, print, or picture to be worked into or worked on, or printed, or painted, or cast, or otherwise fixed on any article of manufacture.

5. A new and original shape or configuration of any article of manufacture.

The first three of these cla.s.ses would seem to refer to ornament only; the fourth to ornament, combined with utility, as in the case of trade marks; and the fifth to new shapes or forms of manufactured articles, which, for some reason, were preferable to those previously adopted.

The disputed questions which have thus far arisen under these definitions are:

1. What variations may be claimed or covered by the patent consistently with unity of design.

2. Is a new shape of an article of manufacture, whereby utility is secured, a subject of protection under this act; and

3. Is mechanical function of any kind covered by it.

As to the first of these questions, it seems to have been a.s.sumed that the design spoken of in all parts of the sections referred to covered a fixed, unchangeable figure, that the protection of letters patent did not extend to any variation, however slight, but that such variation const.i.tuted a new design, might be covered by a new patent, and might safely be used without infringement of the first. This, it is said, is the correct theory of the law, and has been the uniform adjudication of the Office.

Neither of these statements is absolutely correct. The law by no means defines a design with such strictness. The language is, "new and original design for a manufacture," "new and original impression or ornament," "new and original shape or configuration." It would seem to be too plain for argument, that the new design, or impression, or shape, might be so generic in its character as to admit of many variations, which should embody the substantial characteristics and be entirely consistent with a substantial ident.i.ty of form. Thus, if the invention were of a design for an ornamental b.u.t.ton, the face of which was grooved with radial rays, it would seem that the first designer of such a b.u.t.ton might properly describe a b.u.t.ton of five rays, and, having stated that a greater number of rays might be used, might claim a design consisting generally of radial rays, or of "five or more" rays, and, that it could not be necessary for him to take out a patent for each additional ray that could be cut upon his b.u.t.ton. So, if the design were the ornamentation of long combs by a chain of pearls, it would seem that a claim for such a design might be maintained against one who arranged the pearls, either in curved or straight lines, or who used half pearls only, and that such modifications if they had occurred to the designer, might properly have been enumerated in his specification as possible and equivalent variations. In short, I can see no reason, under the law, why designs may not be generic, why what are called "broad claims," may not be made to them, and why the doctrine of artistic or aesthetic equivalents may not be applied to them.

This has been recognized to a greater or less extent in the adjudications of the courts and in the practice of the Office.

One of the reported cases is that of Booth _vs_. Garelly 1, Blatch 247.

The design is described as consisting of "radially formed ornaments on the face of the molds or blocks of which the b.u.t.ton is formed, combined with the mode of winding the covering on the same, substantially as set forth, whether the covering be of one or more colors." The specification, in "substantially" setting forth the design, contained this language: "It will be obvious from the foregoing that the figures can be changed at pleasure by giving the desired form to the face of the mold by depressions and elevations which radiate from a point, whether in the center of the mold or eccentric thereto."

In the consideration of the case by the Court no objection was made to this statement or claim. In the case of Root _vs_. Ball, 4 McLean 180, the learned judge instructed the jury that "if they should find that the defendants had infringed the plaintiff's patent by using substantially the same device as ornamental on the same part of the stove they would, of course, find the defendant guilty. To infringe a patent right it is not necessary that the thing patented should be adopted in every particular; but if, as in the present case, the design and figures were substantially adopted by the defendants, they have infringed the plaintiff's right. If they adopt the same principle the defendants are guilty. The principle of a machine is that combination of mechanical powers which produce a certain result. And in a case like the present, where ornaments are used for a stove, it is an infringement to adopt the design so as to produce substantially the same appearance."