2 APPENDIX. 



Some years since, experiments were tried by Messrs. Maudslay and Field, and an appa- 

 ratus adapted to marine boilers, the purpose of which was, that the water of the boilers 

 should at all times be maintained at the same temperature and at the same degree of con- 

 centration ; and I am not aware of any experiments for such an object prior to these. It 

 resulted from their investigations, that sea water boiling under a pressure of 1\ Ibs. on the 

 square inch, (the usual low pressure standard,) will arrive at 226 Fahrenheit in 24 hours, 

 at 230 in 48 hours, and 232 in 60 hours, Sic. ; at which period it will contain ^ of 

 its bulk of salt. At 232 saturation takes place, and salt (muriate of soda) will be crystal- 

 lized and deposited ; the concentration having progressed from 222, the temperature exhi- 

 bited at the commencement of the experiment. The boilers of course receive only the 

 necessary supply of water for evaporation ; in the above instance 16 gallons per minute. 

 These experiments I have frequently repeated under varied circumstances with correspond- 

 ing results. 



Sea water containing -fa of its bulk of salt, and the quantity evaporated being entirely 

 fresh or distilled water, it is evident that all the salt injected remains in the boilers : the 

 specific gravity of the water is thus constantly increased, and the salt, now more tenacious 

 of its water of solution, requires an increase of heat to separate it ; so that with an uniform 

 heat evaporation would proceed proportionally slower ; but the necessities of the engines 

 requiring that it should proceed at all times equably, the fires must be urged accordingly. 

 The temperature thus increasing (under the same pressure) with the saturation, a thermo- 

 meter becomes a practical register of the density of the water ; of the waste of fuel, to a 

 certain extent ; and a certain index of the danger to which the furnaces are exposed. 



3. A particular arrangement was adopted in the above experiments : a thermometer was 

 applied to the front of the boilers, ranging from 210 to 250 or 300 Fahrenheit, the bulb of 

 which was immersed in mercury, contained in an iron box, protruding into the water of the 

 boilers through the front thereof, so as invariably to partake of the same temperature ; and so 

 that its state could always be known by inspection. To apply the thermometer to boilers 

 generally, it would be necessary to graduate it to suit the particular pressure on the safety 

 valve, the boiling point varying accordingly. An objection may be offered, that the thermo- 

 meters thus applied are very liable to get out of order. To prevent errors of this kind, a 

 common Fahrenheit's thermometer may be employed without reference to the pressure on the 

 safety valve, by immersion in water drawn from the boilers at regular intervals, and boiling 

 under the pressure of the atmosphere ; which, if possible, should be noted when nice 

 observations are required. 



Now, as muriate of soda is an exception to the general law of the solution of salts in 

 water, as scarcely any more is taken up at a boiling heat than at a moderate temperature, 

 it is clear that this boiling in the air exhibits the exact state of the brine, whether from a high 

 or a low pressure boiler ; the thermometer alike showing its specific gravity, and of course 

 acting near enough for this purpose as a hydrometer. In this way the experiments referred 

 to in this paper have been made. 



4. An essential part of the apparatus alluded to for equalizing the concentration of salt 

 in the boilers, was a pump, technically called a brine pump, the particular office of which 

 was to extract from the lowest part of the boilers, at each stroke, a certain aliquot part of the 

 water supplied by the feed pump. One-fifth of the quantity injected was found to be that 



