APPENDIX. 



L O N MARINE BOILERS. 

 BY MR. J. DINNEN, 



ASSISTANT ENGINEER, HER MAJESTY'S DOCKYARD, WOOLWICH. 



1. THE paucity of information connected with steam navigation, a subject, it must be 

 allowed, of great national importance, and which has assumed a prominent feature in her 

 Majesty's naval service, suggested the investigations from which the following practical 

 essay on marine boilers has resulted. The incrusted state of the boilers of all steam vessels 

 returning from the Mediterranean with mails, in the early stage of their employment, was 

 calculated to impress the observer with the impracticability of making such voyages without 

 submitting to like effects ; no experiment having been made, or correct data furnished, at that 

 period, to counteract the notion, so universally entertained, that the water of the Mediterra- 

 nean holds more marine deposit in solution than that of the Channel. It is probable that 

 Dr. Halley's experiments on the evaporation of water from the surface of the sea assisted 

 materially in the formation of this general opinion. 



It is calculated that the Mediterranean evaporates no less than 5,280,000,000 tons daily : 

 and this quantity far exceeds that evaporated from any other surface of equal extent, 

 being entirely encircled by land ; but it does not follow from this that the water is salter. 

 Whoever has been in the Mediterranean is aware that the dews there are exceedingly heavy, 

 and that they begin to descend some time before the sun has set : in still evenings indeed 

 the dew descends where it has arisen ; and no doubt much is precipitated on the land ; but it 

 must be borne in mind, that land gives forth exhalations at all temperatures, as well as the 

 sea. Again, the visible current always runs into the Mediterranean, in addition to the great 

 rivers Nile, Danube, Rhone, &c., to supply that portion of water which the land may carry 

 off. Experiments do not show the specific gravity to exceed that of other waters ; and hence 

 the general opinion alluded to must have been conjectural, and not founded on the result 

 of investigation. 



2. It cannot be too generally known that the thermometer is a good practical test of the 

 concentration of a boiling solution of salt ; of which the following is offered in illustration. 



