REMEDIES. 



column of mercury contained in a siphon tube, and the difference 

 of the levels of the two surfaces of the mercury, would thus 

 become a measure of the saltness of the water in the boiler. A 

 self-registering instrument, founded on this principle, formed part 

 of the self- registering steam-log which I proposed to introduce 

 into steam- vessels some time since. 



38. The Messrs. Seaward of Limehouse adopted, in some of 

 their engines, a method of indicating the saltness of the water, 

 and of measuring the quantity of salted water or brine discharged 

 by blowing out. A glass-gauge, similar in form to that already 

 described in land engines, is provided, to indicate the position of 

 the surface of the water in the boiler. In this gauge two hydro- 

 meter balls are provided, the weight of which in proportion to 

 their magnitude is such, that they would both sink to the bottom 

 in a solution of salt of the same strength as common sea water. 

 When the quantity of salt exceeds ^ parts of the whole weight 

 of the water, the lighter of the two balls will float to the top ; 

 and when the strength is further increased until the proportion 

 of salt exceeds ^ parts of the whole, then the heavier ball will 

 float to the top. The actual quantity of salt held in solution by 

 sea water in its ordinary state is ^ part of its whole weight ; 

 and when by evaporation the proportion of salt in solution has 

 become ^ parts of the whole, then a deposition of salt commences. 

 With an indicator such as that above described, the ascent 

 of the lighter hydrometer ball gives notice of the necessity for 

 blowing out, and the ascent of the heavier may be considered as 

 indicating the approach of an injurious state of saltness in the 

 boiler. 



The ordinary method of blowing out the salted water from 

 a boiler is by a pipe, having a cock in it leading from the boiler 

 through the bottom of the ship, or at a point low down at its side. 

 Whenever the engineer considers that the water in the boiler has 

 become so salted, that the process of blowing out should com - 

 mence, he opens the cock communicating by this pipe with the 

 sea, and suffers an indefinite and uncertain quantity of water to 

 escape. In this way he discharges, ' according to the magnitude 

 of the boiler, from two to six tons of water, and repeats this at 

 intervals of from two to four hours, as he may consider to be 

 sufficient. If, by observing this process, he prevents the boiler 

 from getting incrusted during the voyage, he considers his duty 

 to be effectually discharged, forgetting that he may have blown 

 out'many times more water than is necessary for the preservation 

 of the boiler, and thereby produced a corresponding and unneces- 

 sary waste of fuel. In order to limit the quantity of water 

 discharged, Messrs. Seaward adopted the following method. In 



139 



