May 2nd, 1887.] 



SCIENTIFIC NEWS. 



59 



is shown in Fig. 18 and the section in Fig. 19. The piping 

 in which the hot water is circulated in the building is a con- 

 tinuation of the coil, and a further peculiarity of this system 

 is that there is no opening or vent in the whole of the 

 piping, so that the water in it is hermetically sealed, and its 

 temperature can be raised above the ordinary boiling-point 

 without it being converted into steam. Provision, however, 

 is made for the accumulation of the contained air, and for 

 expansion of the water, by having one or more tubes of 

 larger diameter placed above the highest level of the circu- 

 lating pipes. A tube is also provided at the highest point 

 for charging the apparatus with water without filling the 

 expansion tubes. In this system the circulation obeys the 



Fig. 22. 



Fig 23. 



same laws as those we have already considered. The 

 water is heited in the coil placed in the furnace ; it then 

 becomes lighter, and rises quickly to the highest point in 

 the circulating pipes. As it travels further, it is cooled by 

 conduction and radiation, and in so doing it becomes 

 heavier, and this causes an unequal pressure in the ascenc- 

 ing and descending pipes, and a continuous circulation is 

 established. 



The Perkins small tubes occupy little space, and are not 

 unsightly; moreover, it is comparatively easy to carry out 

 v.'ith them a complicated system of piping, because the 

 pipes are made of wrought-iron and arc of small diameter. 

 For these reasons they are much used for the healing of 

 rooms in dwelling and business houses, especially when 

 several floors have to be provided for. An illustration of 

 this is given in Fig. ^o, in which A is the furnace; 

 B, a room heated by a coil of pipe ; C, C, rooms 

 heated by pipes placed behind the skirting, and covered 

 with cast iron gratings; D a staircase heated by a 

 coil of pipe ; E,E, rooms heated by pipes fixed to the walls 

 or skirting, and covered or not with gratings as desired ; F 

 expansion tube; G filling pipe; II cold water cistern; K 

 cistern heated by a coil of pipe ; M bath supplied with hot 

 water from K. With large pipes the difficulty and expense 



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p o o o 



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Fig. 24. 



of carrying out such a system would be excessive, but for 

 churches, glass-houses, and buildings in which the rooms to 

 be heated are on one or two floors, the larger pipes and 

 larger volume of water are preferable. On the other hand, 

 when the quantity of water in the pipe is small, it can soon 

 be heated, but for the same reason its temperature will soon 

 fall should the fire be neglected. 



Apart from these considerations, the chief difference in the 

 two systems is that the one has a large heating surface with 

 water at a comparatively low temperature, and the other 

 a small heating surface with water at a relatively high 

 temperature. Speaking generally, the latter is more effi- 

 cient than the former, because the greater the difference 

 in temperature between the pipes and the rooms to be 

 heated, the more rapid is the transference of heat. On 

 principle, therefore, the Perkins system has this advantage, 

 in addition to those already referred to ; but it is right to 

 point out some practical considerations in addition to 

 those already mentioned. It should be remembered, for 

 instance, that our comfort depends greatly not only on the 

 warmth of the air we live in, but on its feeling sufficiently 

 dry or moist, as the case may be. By this it must not 

 be supposed that the quantity of moisture is increased or 

 diminished, but that the capacity of air to absorb moisture is 

 increased when the temperature is raised. Our judgment is, 

 in fact, independent of the actual quantity of moisture present, 

 and in summer or winter we talk of the air being either dry 

 or cold, not because there is any difference in the quantity 

 of moisture present, but because in summer the capacity of 

 the air to absorb moisture is greater, whereas in winter the 

 atmosphere is nearly saturated. With the Perkins system, 

 it will easily be understood that as the temperature of the 

 pipes is high, so the air which has been in contact with them 



26. 



becomes thirsty for moisture, and consequently there is a like- 

 lihood of moisture being too rapidly absorbed from the skin of 

 persons living in rooms so heated. It is, therefore, essential to 

 accompany such a system of heating with efficient means of 

 ventilation, to insure a good supply of fresh air and sufficient 

 moisture to give a feeling of comfort to those present. 



So far we have dealt with boilers heated by fires, but 

 before passing to another branch of our subject we should 

 mention that during the last few years a considerable num- 

 ber of gas-heated boilers have been used for moderate 

 lengths of piping. The best of these with which we are 

 acquainted is that shown in Fig. 21, and made by Messrs. 

 Hartley and Sugden, of Halifax, In this there is a water- 

 way on two sides, and these water-ways are connected b}' a 

 large number of horizontal copper tubes, so that water can 

 circulate through them freel}'. The tubes are heated by 

 jets of gas underneath, the products of combustion being 

 carried off by a suitable flue pipe. Inside the lower 

 part of the flue pipe there is an inner tube, tapered and 

 closed at both ends, and as this becomes heated it prevents 

 the condensation of the water vapour which forms a con- 

 siderable portion of the products of combustion. This 



