606 PROCEEDINGS OF SECTION H. 



Since that time the efficiency obtainable has been but little im- 

 proved npon, but many improvements have been introduced, chiefly 

 in the direction of economy and strength of construction. It is 

 reported that several of the water tube boilers at the present 

 Chicago Exhibition are cajmble of giving results close on 13lbs. 

 evaporation per pound of nett combustible with coal. Unfortu- 

 nately no results such as this can be made for comparison with 

 those just quoted, because the fuel used is in every case liquid 

 fuel. It is a noteworthy fact that every boiler which is in use at 

 the Chicago Exhibition belongs to the Avater tube type. 



Mr. George Barrus, in a book on boiler tests (1891), gives, as 

 the result of seventy-one boilers tested Ijy him, the highest place 

 to a water tube boiler with an evaporation of 13-Ollb- Turning to 

 Europe we find the Belleville boiler in favor in France about thirty 

 years ago, and from that date till now a great number of different 

 water tube boilers have come into favor, among others the 

 D'Allest, the Normand, and the Du Temple. 



Here it is remarkable that this type of boiler has been almost 

 exclusively used in the naval and merchant marine, as will be more 

 fully explained elsewhere, while in America and other countries 

 where the water tube boiler is in favor it has been excluded from 

 marine service, with the exception of the torpedo boilers, such as 

 the Mosher in America and the Yarrow and Thornycroft boilers in 

 England, these being adopted on account of the small grate area 

 with light weight and the advantage of safety they offer in action, 

 but they are far from economical in first cost or maintenance. 



In Germany the types of boiler which have been used for many 

 years (e.g., the Tenbrink) would naturally lead to the water tube, 

 and, with the exception of America perhaps, there is no place 

 where it has been more universally adopted. 



At the recent Frankfort Exhibition all the steam was raised in 

 boilers of this type. 



In England, where these boilers^' have been long discredited, 

 they are steadily gaining in favor, and are now much used for 

 electric lighting ; and even the Admiralty are moving from their 

 stolid conservation so far as to institute comparative trials between 

 torpedo boats fitted with water tube and fire tube boilers, and, 

 more wonderful still, have decided that the new torpedo catcher 

 " Speedy" is to be fitted with Thornycroft water tube boilers. 



So rapidly have the new forms of water tube boilers developed 

 that it is not easy to follow the evolution of each, and class it 

 accordingly. In a broad way we stated at the beginning of this 

 paper that there are two main classes — (1) boilers in which water 

 jackets are connected by water tubes. To this class belongs each 

 of the following excellent types: — The Heine (a very efficient and 

 cheap boiler), the Lagrafel D'Allest (the favorite boiler in the 



* The writer does not call an internally fired boiler fitted with galloway tubi;s " a water 

 tube boiler." 



