Among the most important causes of fires in manufacturing establishments, says the " Bulletin of the National Association of Wool Manufacturers," for July, is danger from steam pipes; the danger being greater because the steam or hot-water pipes being introduced as a measure of precaution against fires, liability from fire is not apprehended from that source. Steam and hot-water pipes are often suffered to remain in contact with wood-work, and frequently packed with charcoal or sawdust to prevent radiation. The foil owing facts illustrate the danger of these practices : The ofiicers of the insurance companies charged with the examination of mills, remark upon the general prevalence of the impression that there is no danger of ignition from steam pipes. An insurance officer, visiting mills at Exeter, N. H., observed a steam pipe running through a partition, and in contact with the wood-work. The agent, although incredulous of danger, promised to cut out the wood around the pipes. A few days afterwards the wood was removed where-ever in contact. In the course of the examination, timbers in contact with the pipe, at a distance of three hundred feet from the boiler, were found to have been on fire. The pieces which were shown to me were completely charred. My informant stated the following case to the agent, who incffeduloualy inquired, " Did you ever know a case where steam pipes set wood on fire " At the Oneco Mills, in Sterling, Conn., there being no steam-heating apparatus, a detached tubular boiler was placed in a building at some distance from the mill, to supply steam for heating and for running a donkey engine to assist the water wheel. A steam pipe two and a half inches in diameter, for conveying the steam to the mill, passed through the wall of the boiler house, then ran perpendicularly to the ground, and under ground into the mill. To prevent condensation of the steam, the pipe was inclosed in a tight box of wood filled with powdered charcoal. All worked well for ten lays, when a fire took place in the horizontal inclosing box, lear the boiler house—supposed to be from a spark from the )oiler—then in the perpendicular portion of the inclosing box, md finally in the part under ground." The facts before stated is to the ignition of charcoal, show that spontaneous ignition N&6 the almost inevitable result of this contact of charcoal mth hot-air pipes. Where It is desired to prevent radiation from steam pipes and boilws, it would be well to adopt the plan recommended by Prof. Tyndall in his lectures on " Heat la a Mode of Motion," who observes that " there are cases where sawdust, chaff, or chaKJoal could not be used with safety [to prevent radiation from eteam pipes), on account of their combustible nature. In suck cases powdered gypsum may be used with advantage. In the solid crystalline state it is incomparably a worse conductor than silica, and it may be safely inferred that in the powdered state its imperviousness far transcends that of sand, e&ch. grain of which is a good conductor. A jacket of gypsuu powder around a steam boiler would materially lessen its bss of heat." Mr. Braidwood, whose va* experience gives great weight to his opinions, earnestly warns against the danger from steam and hot-water pipes. He says: " There appears to be j 3ome chemical action between heated iron and timber, by which heat is generated at a much lower temperature than is accessary to ignite timber unler ordinary circumstances. No satisfactory explanation of t4s fact has yet been given, but there is abundant proof that aich is the case. In heating by hot-water pipes, those hermetcally sealed are by far the most dangerous, as the strength of ihe pipes to resist the pressure is the only limit of the heat to srhich the water, and of course the pipes, may be raised. In sone cases a plug of metal which fuses at 400, is put into the pi)es, but the heat to which the plug is exposed will depend veiy much on where it is placed, as however great may be the heat of the exit pipe, the return pipe is comparatively cool. Bmeven where the pipes are left open the heat of the water at th furnace is not necessarily at 313'. It is almost needless to lay that 312 is the heat of boiling water under the pressureof one atmosphere only; but if the pipes are carried sixty or leventy feet high, the water in the furnace may be under the pressure of nearer throe atmospheres, and therefore the heat will be proportionably increased. Fires from pipes for heating by hot water have been known to take place within twenty-four hours after first heating, and some after ten years of apparent safety." Mr. Braidwood, in his testimony before a committee of tho House of Lords, in 1846, stated that it was his belief that by long exposure to heat, not much exceeding that of boiling water, 212, timber is brought into such a condition that it will fire without the application of a light. The time during which this process of desiccation goes on, is, he thinks, from eight to ten years. The writer in the London Quarterly, before quoted, says that Mercers' Hall, in London, built in 1853, was the victim of its hot-water pipes; the woodwork in the vaulted rooms ot the British Museum, containing the Nineveh marbles, was fired in a similar manner, and the new Houses of Parliament have been on fire several times already from a similar cause. The most cautious insurance companies, taking in view tho absolute danger from steam pipes, unless most carefully fitted, and the common belief that there is no danger, which prevents the requisite care, regard the system of heating by steam pipes as ordinarily no safer than heating by anthracite stoves, or by burning wood in a box stove well fitted up—as the visible presence ot the fire induces carefulness. Still the system of heating by steam is prefeiTod when the pipes are well fitted, and all contact with combustible matter prevented. It is better that the boiler should be outside in a building erected for the purpose. When the pipes pass through a floor they should be surrounded with an iron plate or flange. The inner rim of the flange should be provided with points touching the pipes, so that a constant current of air should pass through. The danger in heating by horizontal smoke flues, although they are rarely used in mills except for drying purposes, is greater than in the use of steam pipes. As the whole of the draft must pass through the fire, these flues, if not properly built, are dangerous through their whole course. This is observed in the market green-houses which formerly were generally heated by such flues. The author of " Practical Floriculture and Gardening for Profit," Mr. Peter Henderson, says: " Too great caution cannot be used in keeping wood-work away from the flue and chimney at the furnace end; and for fifteen feet of the hot end of the flue, wood should nevr be placed nearer than one foot. Do not listen to what your builders may say, as few of them have had experience in such matters ; and whatever they may pretend, not one in a dozen knows more about what is dangerous from a fire than you do yourself." After mentioning several instances to show the necessity ol the utmost caution in the use of this mode of heating, he remarks that, " Every winter there are hundreds of fires originating in green-houses by the wood-work taking fire from flues." Although gas, if carefully laid on and properly used, is safer than any other light, it is important that much care should be exercised in the location of the jets. Gas-burners are dangerous when placed near a ceiling. Mr. Braidwood mentions an instance where a gas-light set fire to a ceiling twenty-eight inches and a half from it. The papers, as I am informed, have recently published a statement of a similar instance which occurred at Pittsfield, Mass. Mr. Eyre M. Shaw, superintendent of the London fire department, in 1862, and the successor of Mr. Braidwood, lays down the rule that "jets or movable gas brackets should never be less than thirty-six inches from the ceiling over it. They should be protected on top by hanging shades, and on the sides by stops on the several joints, which should prevent brackets from moving more than a safe distance." " Attention," he says, " should be called to the very common and dangerous practice of nailing tin or iron on adjoining timbers. This has long proved to be* no protection, and it has the disadvantage of allowing the-timber to be charred completely through before it is known.** Fires often proceed from carelessness in lighting gas. Mr.Braid* 146 wood relates that, some years ago, upwards of 100,000 were lost through the partner of a large establishment in England lighting gas with a piece of paper, which he threw away, and thiis set fire to the premises, although it was a strict rule in the place that gas should only be lighted with tapers, which were provided for that purpose. It is hardly necessary to dwell upon the more obvious causes of fire common to all structures—such as carelessness in the use of matches, and the dropping of fire from unextinguished tobacco—the latter a constantly occurring source of conflagrations, figuring largely in the causes of fires in London; the ratio of fires for a series of years from this cause, as compared with those from spontaneous combustion, being as 166 to 43. The smoker's match, carelessly thrown away, has become a social nuisance, the great source of general confiagra-tions now-a-days. One insurance company in London has lately reported that its losses by Inciter matches alone amount to not less than 10,000 annually. Special notice should be taken of a hitherto unsuspected cause of fires in mills, first noticed by the eminent mill engineer, Mi . James B. Francis, who describes, in a communication to the Journal of the Franklin Institute, the circumstances of the ignition of pine timber in the Appleton Cotton Mills, in 1864, through electrical sparks communicated from a rapidly moving leather belt. The belt was driven by a drum eleven feet in diameter, having iron arms and wooden lagging, making ninety-two revolutions, and transmitting a horse-power estimated at one hundred and seventy-five. The pulley driven by the belt was six feet in diameter, and entirely of iron. The peripheries of both drum and pulley were covered with leather. The belt was made of two thicknesses of leather cemented together, and about three eighths of an inch thick. It had been slightly greased on the inside seven or eight weeks before the fire with a mixture of tallow and neat's-toot oil. The part of the belt near the timber was the slack side, running nearly vertically, and at the nearest point was about eight inches from the timber. When it was first observed by Mr. Francis, a constant stream of sparks was passing between the belt and the corner of the timber which had been on fire. The charred timber indicated that about six inches of the corner had been on fire. The electrical excitement in the mill on the day of the fire had been unusually great, although electrical phenomena, frequently observed in cotton and woolen mills, usually attract but little attention. Mr. Francis observes that it is not unfrequent to find, on the belt boxes of a mill, an accumulation of fiyings of cotton or wool covering every thing not in rapid motion, to a sensible depth. In this case the belt box was very clean, to which fact he attributes the slow progress of the fire, and the detection of its cause. He also remarks " that by the light of the fire at the Appleton Mills, it appears probable that many other fires which were totally inexplicable at the time of their occurrence, may be attributed to this cause."