USE AND EFFECT OF SALINOMETERS. 189

efficient as a non-conductor of corrosiveaction.

Now as to the quantity of the sea waterto he admitted, practice is the best teacher ;and selecting, therefore, one example of certainauthenticity amongst others, the following isthe result. In a steam vessel fitted with en ginesof 350 horse-power—nominal,:—collectively—surface condensation and superheated steambeing adopted—sixteen to twenty gallons ofsea water per watch of four hours was intro-duced in the tank, and the boiler was therebyscaled about a thickness of one-sixteenth of aninch only in three months. This sediment wasremoved at intervals by blowing out, whenin port after the fires were extinguished ; in afew hours the scale cracked, and a brush onlyrequired to cause its effective removal; also theplates showed no indications of corrosion orwear. This mode of treating a boiler havingbeen proved to he efficacious after some years’trial, it remains but for others to adopt thesame with an equal result.

USE AND EFFECT OF SALINOMETERS.

The salinometer bears such a near relationto the marine boiler in the present day, andits adoption being in strict allusion to incrusta-tions, it has been thought expedient to add anotice of the use, and description of the same, asa conclusion to the present chapter. In render-ing its practical utility obvious, the system ofcondensation will not he considered; as the in-strument in question is essential in either case.

Until the introduction of salinometers, theprocess of testing the density of the water inthe boilers was accomplished by blowing outor off, and this was done at intervals, deter-

mined by the random judgment of the personin charge. It is obvious, however, that if thisoperation is performed too often, water may beblown out which has not yet reached the de-gree of saltness requiring the same. The conse-quent introduction of more cold sea water intothe boiler will cause increased consumption offuel to restore the lost heat, and it is estimatedthat from this cause the firemen are compelledto feed the boiler at least one-fourth oftener.On the other hand, should the operation of blow-ing out not he performed at the proper periods,incrustation may take place to a highlyinjurious degree in a very short space of time.It will, therefore, be at once apparent, that it isof the highest importance that the engineershould be able at all times to ascertain withprecision the density of the water in his boiler.In order to do this, an adaptation of thehydrometer, graduated for the special use towhich it was to be applied, was made, and soonobtained favour with marine engineers. As,however, every time it was necessary to usethis instrument, water had to be drawn into acan or bucket, and as in rough weather thiswas a feat almost impossible of achievement,it soon occurred to Mr. Sewell, a practicalAmerican engineer, that for the proper and con-stant use of this instrument—more especially itsadoption in connection with the thermometerwithout which its indications are not thoroughlyreliable—it should he provided with a fixed casem which it could float freely, and m which thehydrometer’s indications, together with those ofthe thermometer, might at all times be seen ;also that the combined instruments and theircase, forming altogether the “ salinometer,”should be rendered a continuous indicator by