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o make it appear in a manner perfectly satisfactory to my readers that I have not ventured to give this opinion but upon good and sufficient grounds。
Those who will take the trouble to consider the nature and properties of elastic fluids；of air；smoke；and vapour； and to examine the laws of their motions； and the necessary consequences of their being rarified by heat； will perceive that it would be as much a miracle if smoke should not rise in a Chimney； （all hindrances to its ascent being removed；） as that water should refuse to run in a syphon； or to descend in a river。
The whole mystery； therefore； of curing smoking Chimnies is comprised in this simple direction。 FIND OUT AND REMOVE THOSE LOCAL HINDRANCES WHICH FORCIBLY PREVENT THE SMOKE FROM FOLLOWING ITS NATURAL TENDENCY TO GO UP THE CHIMNEY； or rather； to speak more accurately； which prevents its being forced up the Chimney by the pressure of the heavier air of the room。
Although the causes； by which the ascent of smoke in a Chimney MAY BE obstructed； are various； yet that cause which will most commonly； and I may say almost universally be found to operate； is one which it is always very easy to discover； and as easy to remove；the bad construction of the Chimney IN THE NEIGHBOURHOOD OF THE FIRE…PLACE。
In the course all my experience and practice in curing smoking Chimnies；and I certainly have not had less than five hundred under my hands； and among them many which were thought to be quite incurable；I have never been obliged； except in one single instance； to have recourse to any other method of cure than merely reducing the Fire…place and the throat of the Chimney； or that part of it which lies immediately above the Fire…place； to a proper form； and just dimensions。
That my principles for constructing Fire…places are equally applicable to those which are designed for burning coal； as to those in which wood is burnt； has lately been abundantly proved by experiments made here in London； for of above an hundred and fifty Fire…places which have been altered in this city； under my direction； within these last two months； there is not one which has not answered perfectly well＇1＇。And by several experiments which have been made with great care； and with the assistance of thermometers； it has been demonstrated； that the saving of fuel； arising from these improvements of Fire…places； amounts in all cases to more than HALF； and in many cases to more than TWO THIRDS of the quantity formerly consumed。Now as the alterations in Fire…places which are necessary may be made at a very trifling expence； as any kind of grate or stove may be made use of； and as no iron work； but merely a few bricks and some mortar； or a few small pieces of fire…stone； are required； the improvement in question is very important； when considered merely with a view to economy； but it should be remembered； that not only a great saving is made of fuel by the alterations proposed； but that rooms are made much more comfortable； and more salubrious； that they may be more equally warmed； and more easily kept at any required temperature；that all draughts of cold air from the doors and windows towards the Fire…place； which are so fatal to delicate constitutions； will be completely prevented；that in consequence of the air being equally warm all over the room； or in all parts of it； it may be entirely changed with the greatest facility； and the room completely ventilated； when this air is become unfit for respiration； and this merely by throwing open for a moment a door opening into some passage from whence fresh air may be had； and the upper part of a window； or by opening the upper part of on window and the lower part of another； and as the operation of ventilating the room； even when it is done in the most complete manner； will never require the door and window to be open more than one minute； in this short time the walls of the room will not be sensibly cooled； and the fresh air which comes into the room will； in a very few minutes； be so completely warmed by these walls that the temperature of the room； though the air in it be perfectly changed； will be brought to be very nearly the same as it was before the ventilation。
Those who are acquainted with the principles of pneumatics； and know why the warm air in a room rushes out at an opening made for it at the top of a window when colder air from without is permitted to enter by the door； or by any other opening situated lower than the first； will see； that it would be quite impossible to ventilate a room in the complete and expeditious manner here described； where the air in a room is partially warmed； or hardly warmed at all； and where the walls of the room； remote from the fire； are constantly cold； which must always be the case where； in consequence of a strong current up the Chimney； streams of cold air are continually coming in through all the crevices of the doors and windows； and flowing into the Fire…place。
But although rooms； furnished with Fire…places constructed upon the principles here recommended； may be easily and most effectually ventilated； （and this is certainly a circumstance in favour of the proposed improvements；） yet such total ventilations will very seldom； if ever； be necessary。As long as ANY FIRE is kept up in the room； there is so considerable a current of air up the Chimney； notwithstanding all the reduction that can be made in the size of its throat； that the continual change of air in the room which this current occasions will； generally； be found to be quite sufficient for keeping the air in the room sweet and wholesome； and indeed in rooms in which there is no open Fire…place； and consequently no current of air from the room setting up the Chimney； which is the case in Germany； and all the northern parts of Europe； where rooms are heated by stoves； whose Fire…places opening without are not supplied with the air necessary for the combustion of the fuel from the room；and although in most of the rooms abroad； which are so heated； the windows and doors are double； and both are closed in the most exact manner possible； by slips of paper pasted over the crevices； or by slips of list or furr； yet when these rooms are tolerably large； and when they are not very much crowded by company； nor filled with a great many burning lamps or candles； the air in them is seldom so much injured as to become oppressive or unwholesome； and those who inhabit them show by their ruddy countenances； as well as by every other sign of perfect health； that they suffer no inconvenience whatever from their closeness。There is frequently； it is true； an oppressiveness in the air of a room heated by a German stove； of which those who are not much accustomed to living in those rooms seldom fail to complain； and indeed with much reason； but this oppressiveness does not arise from the air of the room being injured by the respiration and perspiration of those who inhabit it；it arises from a very different cause； from a fault in the construction of German stoves in general； but which may be easily and most completely remedied； as I shall show more fully in another place。 In the mean time； I would just observe here with regard to these stoves； that as they are often made of iron； and as this metal is a very good conductor of heat； some part of the stove in contact with the air of the room becomes so hot as to calcine or rather to ROAST the dust which lights upon it； which never can fail to produce a very disagreeable effect on the air of the room。 And even when the stove is constructed of pantiles or pottery…ware； if any part of it in contact with the air of the room is suffered to become very hot； which seldom fails to be the case in German stoves constructed on the common principles； nearly the same effects will be found to be produced on the air as when the stove is made of iron； as I have very frequently had occasion to observe。
Though a room be closed in the most perfect manner possible； yet； as the quantity of air injured and rendered unfit for further use by the respiration of two or three persons in a few hours is very small； compared to the immense volume of air which a room of a moderate size contains； and as a large quantity of fresh air always enters the room； and an equal quantity of the warm air of the room is driven out of it every time the door is opened； there is much less danger of the air of a room becoming unwholesome for the want of ventilation than has been generally imagined； particularly in cold weather； when all the different causes which conspire to change the air of warmed rooms act with increased power and effect。
Those who have any doubts respecting the very great change of air or ventilation which takes place each time the door of a warm room is opened in cold weather； need only set the door of such a room wide open for a moment； and hold two lighted candles in the door…way； one near the top of the door； and the other near the bottom of it； the violence with which the flame of that above will be driven outwards； and that below inwards； by the two strong currents of air which； passing in opposite directions； rush in and out of the room at the same time； will be convinced that the change of air which actually takes place must be very co