184 Transactions of the Horticultural Society. 



necessary for water ; but oil is very inflammable, and sulphuric acid cor- 

 rosive. 



" 17. It is known from experience that the heat which raises the tem- 

 perature of 1 cubic foot of water 1°, will heat 2850 cubic feet of air 1° j 

 consequently, if a be the quantity of air to be heated per minute to / de- 

 grees, and x be the difference of the temperature of water in the apparatus, 

 then 



2gKQ=^'^') or, gtirf) J = w = the quantity of water m cubic feet that must 



flow along the pipe per minute to supply the heat ; and the quantity being 

 equal to the velocity per minute multiplied by the area of the pipe ; the 

 means of knowing whether the pipes be capable of allowing the proper 

 quantity to flow along, or not, becomes easy; as well as of fixing the 

 proper diameter. If any other liquor be used, the number 2850 should be 

 multiplied by the specific heat of that liquid; and then proceed as before. 



" 18. The least quantity of liquid the apparatus could contain is double 

 the quantity cooled during the time of making one circuit in the pipes, 

 which is found by dividing the quantity w, as found above, by the number 

 of circuits or parts of a circuit made in a minute, and comparing the velo- 

 city with the length of the pipes. Whatever the quantity is in excess 

 above this, is to be considered a reserve of hot fluid to afford heat after the 

 fire is out ; and the fire must be so much earlier lighted as to heat this 

 excess of water, as it must be hot before the surface can afford its effective 

 supply of heat. Hence, there is a considerable objection among gardeners 

 to large boilers and large reservoirs. 



" 1 9. But the most important of the properties of the hot-water method, 

 as first tried, consists in the power it has of keeping up the temperature 

 of the house, for a long period, without attention from the attendant ; and 

 it is entirely owing to the excess of fluid that it has this advantage over 

 steam heat ; and the exact knowledge which we now have of the heat 

 which water contains in proportion to its temperature, enables us to calcu- 

 late the time the cooling of the fluid will maintain the heat of a house ; for 

 iftibe the number of degrees the water is above the temperature of the 



At 



house, and tv its quantity in cubic feet ; then, since is the quantity to 



supply the house one minute, = the minutes the temperature of 



A f 



the house will be sustained by the cooliug of the water longer than in a 

 house heated by steam alone. It will be obvious, the actual time of cooling 

 will be more than twice this time, and the heat afl'brded to the house will 

 decrease ; but this is in some measure compensated for by the solid parts 

 of the house receiving an excess while the apparatus is in full action, or 

 boiling, and which it affords again as the house cools; a compensation 

 taking place in this manner, which renders it easy enough to proportion 

 the quantity of reservoir with as much certainty as is necessary. 



" 20. The ordinary method of making reservoirs and boilers so large as 

 to answer the purpose of maintaining the heat during the night, has the 

 objection already noticed of rendering it a considerable time before the 

 apparatus can be raised to a temperature capable of giving much heat ; and 

 it appears to me that it would be a material improveinent to heat the water 

 for a reserve of heat, by passing the pipes of the apparatus through the 

 water so that its temperature should be slowly raised, and the house 

 receive heat during the time. A small proportion of surface of pipe will 

 heat the water, because water abstracts heat from a heating surface with 

 about twenty times the rapidity that air does at the same temperatures ; 



