192 USE AND EFFECT OF SALINOMETERS.

boiler cannot attain a greater degree of salt-ness than ^; from which it will he seen that,to keep the water in the boiler at that density,one-quarter of the water that enters must beblown out ; and to keep it at one-half must

be blown out, and in a similar proper propor-tion for any other density when using sea-water.

The hydrometer generally used is graduated,marked upon the principle just explained, andis ftg. 0 for fresh water—for sea water,which contains lib. of salt to 321bs. of water—3 % when there is 2lbs. of salt to 321bs. ofwater—when there is 3lbs. of salt to 32lbs.of water—and when there is 4lbs. of salt to321bs. of water, and so on. Each division issubdivided into four parts, showing halves andquarters of each.

The hydrometer is also graduated for thetemperature of 200 degrees, it being necessaryto have some standard of temperature at whichthe indications are always to be taken; as steamof different pressures has different temperatures,and as a difference in temperature will alter theindications of the hydrometer, it is, therefore,necessary that the water be relieved from thepressure in the boiler, that it may assume auniform temperature. This it will do under thepressure of the atmosphere, and it is thusaccomplished in this instrument, which rendersit applicable to boilers in which the pressure ofthe steam may vary, or in which either highor low pressure steam is used.

The “ Gathercole-How ” and the “ Long ”salinometers are manufactured by Messrs. Souland Co., of Finsbury-square, who kindlysupplied the working drawings from whichthese presented were reduced.

Enough has been stated to render obvious

the defects common to the use of condensa-tion with marine engines. It will be observed,on reflection, that, although the density of thesea water has been quoted, practically theboiler—even with injection condensers—is fedfrom the tank or discharge pipe, as a rule; andit is only when the donkey or sea-feed pumpis used that the natural sea water is admittedinto the boiler.

The gain with surface condensers is onlycertain when the sea water is partially intro-duced in the distilled-water tank; and in nocase whatever should this be omitted— i. e. aperfect amalgamation of the distilled and seawater should ensue before either enters theboiler. There is a just cause for this, fromthe fact that were the sea water used atintervals in its natural state, an unevenincrustation must result therefrom; and it iscertain, also, that an entire amalgamationcannot ensue in the boiler when the requisiteevaporation is being effected.

Now, with reference to the regulation of thedensity of the water in the boiler, and therebydetermining the amount of natural sea waterto be admitted in the tank, the more efficientmeans is to allow a continual surface exitfrom the boiler, generally termed scummingor surface blow off; by permitting also aneasy discharge through the salinometer, acorrect knowledge of the density of the fluidcontents of the boiler is ensured. An efficientpractice is to preserve a density ■£§- towith surface condensers, and to with

the injection system. As a conclusion to thischapter, it can truly be said that theory basedon correct principles must produce practicalresults.