April 1st, 1SS7.] 



SCIENTIFIC NEV/S. 



where no steam is generated an explosion is impossible ; if 

 the circulation be right, the worst that can happen will be a 

 leakage of water due to the cracking of the boiler or pipes. 

 It is, however, right to add that if the circulation is impeded, 

 the water in the boiler may be overheated, and steam with 

 its attendant risks will be produced. 



Having dwelt on the importance of securing an unim- 

 peded circulation of the water, we will now pass on to 

 consider some points connected with the boilers generally 



Fig. 13- 



used for heating the water. The variety of boilers made 

 for this class of work is very great, but it will be sufficient 

 for our purpose to consider only some tj'pical examples, 

 and these we give in the accompanying illustrations.* 

 Fig. 3 is a wrought-iron rivetted boiler of the saddle type. 

 Fig. 4 is similar in form, but the joints are welded to- 

 gether without rivets; and Fig. 5 is also similar in form, but 

 made of cast-iron. These boilers have the merit of being 

 simple in construction, and can be heated with any kind of 



Fig. 14. 



fuel, but they have not as large a heating surface as Figs. 

 6 and 8, the sections of which are shown in Figs. 7 and 9. 

 Fig. 8 is arranged so that the fuel may be put in at the top, 

 and this is an advantage in some cases. Both these 

 boilers are decidedly good from an economical point of 



* We are indebted to the Thames Bank Iron Company for the 

 illustrations of Figs. 3 to 12, and 14 and 15 ; to Messrs. Weeks and Co. 

 for Fig. 13, and to Mr. James Keith for Figs. 16 and 17. 



view, as there is a free and rapid circulation of water, which 

 means a rapid withdrawal of heat from the fire. Fig. 10 is 

 a modified form of the well-known Cornish boiler, so much 

 used for producing steam. Fig. 11 is a boiler consisting of 

 horizontal tubes, and Fig. 12 is one with vertical tubes. 

 Both heat the water rapidly, but in our opinion are less 

 efficient than Figs. 6 and 8. Fig. 13 is a development of 

 Fig. 12, and is much used. All these boilers have to be set 

 in brickwork, with suitable flues ; but there is another class 

 called independent boilers, which are self-contained, and 

 need no brickwork. Of these, Figs. 14 and 15 are good ex- 

 amples, as the heating surface is large, while the construction 

 is simple, and the circulation of the water is rapid. In Figs. 

 16 and 17 we have an independent boiler of considerable 

 merit and originality. It consists of several sections placed 

 one above the other, and to a certain extent the power of 

 the boiler may be increased or diminished by adding to or 

 reducing the number of sections. 



We have already seen that the circulation of hot water 

 depends mainly on the difference of temperature in the 

 flow and return pipes ; it is, therefore, important not only 

 that the boiler should heat the water quickly, but that the 

 heated water should be able to leave the boiler without 

 check. Also, it is not desirable that the boiler should con- 

 tain a large quantity of water, as within certain limits the 

 smaller the quantity of water the more rapidly it will be 



Fig. 15. 



heated, and the quicker will be its movement and circulation. 

 The boiler is always full of water, and there is little or no 

 danger of any part of it being overheated if well designed, 

 and if kept free from lime and other deposits inside. A 

 wrought-iron boiler heats water more quickly than one of 

 cast-iron, as the metal is thinner, but cast-iron is now 

 extensively used, as it is not only cheaper but corrodes 

 more slowlj'. On the other hand, it requires more careful 

 stoking, especially when the fire is started, as it is unable to 

 bear severe strains of expansion or contraction. It is also 

 important to remember, as a general rule, that the heating 

 surfaces of a boiler are more eftective when they are 

 horizontal than when they are vertical, and this consideration 

 is especially important when a large boiler is required. 

 Care should also be taken to have space enough in the 

 boiler to contain the fuel required for several hours' work. 



In selecting a boiler for a given amount of work, it should 

 be borne in mind that the design of the boiler should to a 

 certain extent depend on the amount of heating it is required 

 to do. For instance, such a boiler as shown in Fig. 10 is 

 more suited to a long length of piping than a short length ; 

 on the other hand, Figs. 14 and 15 are designed for moderate 

 lengths of piping. The following table, however, will assist 

 the reader to compare the relative heating power of the 

 different boilers illustrated, as from data guaranteed by the 

 makers we have given the number of feet run of pipe, 4 

 inches diameter, which each boiler is capable of heating 

 under like conditions of temperature : — 



