As the engineering public is gradually becoming educated to the realization of the economy of keeping boilers clean, a I considerable number of device hate been patented to meet ? the demand for a good tool to clean out flues. Brushes have been tried, but the deposit which forms in flues needs I something more powerful than them for its effectual removal. ! We last week illustrated an improved boiler flue scraper, and this week we lav before our readers a description and engraving of another device for the same purpose, the invention of Mr. E. L. Pratt, deceased, late of Beverly, Mass., a patent for which was granted to II. L. Pratt, administrator, May 11, 1869. This scraper consists of two tapering heads, the broad parts of each facing the other, fixed upon a pipe or rod at a short distance from each other. The broad ends of the heads have mortise-like recesses formed in them, which receive the ends of the cutters ; the mortises being large enough to admit considerable play of the cutters to and from the longitudinal axis of the instrument. Each of the cutters has two cutting edges at right angles with its longitudinal axis/ so arranged that any part of the surface, omitted by the forward one, shall be scraped by the other. These are also contracted in the middle into a shape approximating the section of an hour-glass, so that all the soot falls into the central part of the instrument between the cutters, and is drawn out with it. The cutters are pressed out against the sides of the flues by elliptical plate ; springs,which also permit the scraper to enter and clean flues of various sizes. The cutters are to be made of chilled iron which will render them very durable. From the cutting edges of the cutters extend, toward each head, ribs which facilitate the entrance of the instrument; and they also have a central rib extending between the cutting edges, which facilitates the entering of the hinder cutting edges, while it is sufficiently depressed not to interfere in the least with their operation. The scraper is so cheaply made that it is designed to furnish them for every diameter of tube, and in such case, the cutting edges are made to fit the curvature of the interior surface of the flue. It is claimed tlha.t this scraper is cheaper, more durable, and effective than: ally form of wire brush. Orders souljd be addressed to Miller's Falls Manufacturing Co., 87 Beekm st. New York city. Improved Hose Pipe. This hose pipe combines the solid jet, spreader, and stop cock, in one. It is so constructed that by simply turning, with the thumb and forefinger, the milled nut near the small end, the jet is either entirely checked or diffused in drops, as with the ordinary sprinkler, or fine like mist, so that the most delicate plant may be watered by it without injury. It is simple and compact, and perfectly easy to operate. We have used one of these hose pipes and find it very satisfactory. For florists it is the very thing wanted. Arrangements have been made to supply hose dealers throughout the United States. For particulars address the patentee, F. S. Babbitt, Taunton, Mass. How Granite is Affected by Fire. There are fow people having any connection with the bflilding trade in this country but have an idea of the strength and durability of granite, its excellent qualities for the general purposes to which stone is adapted, rendering it of almost universal utility. Granite is composed of mica, quartz, and felspar, and its quality is easily discovered by the proportion and arrangement of these; but sometimes traces of other minerals are visible, and influence its density and color proportionately. Geologists accept it as an igneous rock, from the fact of its unstratified condition and the perfection of its crystals, which seem not to have been worn by friction as others are that are found in sedimentary formations. An- other peculiarity that it possesses is the quality of indurating or hardening other bodies with which it comes in contact, and this renders it a superior stone for house-building purposes. It is well known that granite walls, if properly built, need no supplementary linings to make them damp-proof, and that mortar will adhere to them and " set " in a manner similar to that which it does when applied to brick. It must not be thought, however, that this peculiarity arises from either porosity or absorption, for experiments have proved that granite is as dense and impervious to moisture as any stone that we possess, except basalt, and consequently its indurating property must be the result of something else—probably, as far as mortar is concerned, of evaporation caused by the latent heat of the stone, such as all pyrogenous bodies are known to possess. But, to be more practical with the subject, we will refer to Wilkinson's experiments on the different varieties of building stone—experiments that were conducted with an amount of care and exactness that leaves little room for doubt as to the accuracy of their results. The average weight of granite he sets down as 170 lbs. per cubic foot, and the quantity of water that it absorbs by immersion about J lb. per cubic foot. The weight of limestone per cubic foot andthe quantity of water that it absorbs, he sets down similarly. Now, from this it is apparent that it is not by absorption that granite maintains dryness, but rather by some other influence that it exercises ; for limestone and it being bulk for bulk of equal weights and equal absorbing tendencies, it might naturally be expected that their damp-resisting qualities would also be equal. Such is not the case, however; for while moisture is unnoticeable on the granite, it appears plentifully on the limestone, or exudes through the plaster in case it is covered, although both stones- may be subjected to the same weather influences. As a fire-resisting stone, granite ranks medium, and, like calp, the inferior qualities are the best adapted to this purpose. In many parts of Ireland where it can be obtained, and where bricks are not available, it is used for lining lime kilns—a requirement for which it has been found very suitable. It sometimes, too, supplies the place of fire lumps in the backing of kitchen grates and in lining ovens, and in such positions answers very well. The harder descriptions yield soonest to the influence of fire, as they " break up " into more regular portions than the softer kind, which rather undergo a wasting process by disintegration. It may be well here to observe that, unlike the generality of building stones, granite will hold together firmly, even though it may be severely fractured. The friction of its component parts, supplemented by the toughness of its mica, acts with a degree of power that requires the exertion of considerable force to effect separation, and this, although its co-h-esire properties are completely destroyed. The general fractures by fire are vertical, and in nearly all cases parallel to the face, but sometimes they traverse the face in different directions, the change chiefly depending on the quality of the stone and the direction of its mia. The granite that we noticed in Messrs. Meade's concerns after the fire was the coping of the wall between their premises and the railway station. The stone is of medium quality. Its projection on that side in contact with the fire was carried off in a line with the face of the wall, but other than this it did not exhibit symptoms of yielding that could be callgd serious, although at times during the fire the flames completely enveloped it. In Messrs. Harrington's con-cerns, too, in Kings'-Inns street, where a terrible fire occurred some years ago, the granite piers and copings withstood the intensity of the heat without sustaining injury beyond the chipping of some projections, and the injury here, as in the former case, we believe to be the result of a reaction, caused by the water coming in contact with the intensely-heated : stones. The opinion on this matter is strongly supported by the fact that in the lining of lime kilns, where granite is submitted to violent heat for considerable periods, it exhibits tolerably fair resisting qualities, never yielding in mass, and but slowly by disintegration. We, therefore, look upon it as a material that may with safety be used in structures intended for fire-proof purposes. —Irish Builder. W. W. CoBCOitAisr, a retired banker, has conveyed to a Board of Trustees, the Corcoran Art Building in Washington, to be held in perpetuity as a free picture gallery. The property is a very valuable one, and Mr. Corcoran proposes to endow the gallery with a cash gift of three hundred thousand dollars. August Belmont, of this city, is going to give a dozen of the most valuable pictures from his private collection as his contribution. Mr. Corcoran's gift aggregates something like one million dollars, and places him among those to be forever spoken of as great public benefactors. It is a noble thing, and,if the money is judiciously expended,the collection will become a source of deep interest and instruction to all classes of our citizens who are able to see it.