The salinometer is an instrument for measuring the quantity of solid matter or mineral salts dissolved in water. The one we now illustrate (taken from the London Engineer^ is intended to be applied to a boiler, to indicate the percentage of mineral salts in the water it contains. It depends on the principle that water containing any dissolved matter boils at a higher temperature than when pure. For instance, pure water boils at 212 Fah. ; a solution of alum at 220 ; a solution of common salt at 224 ; and one of acetate of soda at 256 ; so that by arranging a delicate thermometer and properly graduated scale in connection with the boiler, it is possible to indi. cate the percentage of salts in the water which is being used. In our engraving, A is the boiler, having a pipe, B, and stop-cock, C, connecting with a globe-shaped vessel, D, containing the bulb of a thermometer, d, properly protected from breaking. Part of the vessel, D, is broken away, to show the interior. is the scale, and F a waste pipe, so placed that the excess steam or water can escape, and so allow the water in D to remain at its normal pressure ; that is, at the same pressure as that in the boiler. The operation is as follows :The handle of the stop-cock, 0, is so turned as to admit the water into D, and the percentage and temperature can be read off, and the pointer, e, so fixed that on another trial the last one may be indicated, and a comparison instituted. Of course, the whole depends on the graduation of the scale. It is a simple and useful invention. The Engineer does not say whether it is patented or not.