A paper was real before the institution of Civil Engineers, London, noticed in the Mechanics' Magazine, which contains some interesting experiments in relation to the use of sea water in our steam boilers. There are some difficulties attending its use which are not easily provided for, but perhaps some of our many ingenious inventors may suggest a remedy. It appears by the experiments above referred to, that an increase of heat is required to generate steam from salt water, the boiling point of a solution being above that of pure water in proportion to the quantity of salt dissolved by a constant weight of water. And again there is a waste of fuel necessary to blow off the brine frem the boiler in order to prevent incrustation; it has been suggested that the condensed steam may be used, and thus avoid the accumulation of brine ; this has been tried, and we believe with very good results, although at the expense of an amount ot power sufficient to operate the condenser. It has been also proposed to absorb the caloric from the brine as it passes from the boiler, and retain it for use a second time ; the experiments prove that the increase of temperature of brine above that of pure water was owing entirely to the salt, for the steam arising from both waters were of the same temperature under similar pressures. The loss ot caloric by the use of this water was owing to the salt dissolved, which retained the heat in a latent state. The losses to be estimated for blowing off the brine were the power necessary to discharge, and restore the deficiency by feed water—the injection of feed water; and the loss of capacity for heat of the solution. Estimates were made upon two boilers ot different dimensions with feed and steam of each different temperatures, from which it appeared that the most economical system was to blow out one-sixth, at intervals varying from 6 to 10 hours, working from a density of 30 to 35 . Data were obtained of the specific gravity ol different waters which showed a variation of from 1026 to 1031. The water from inland seas being often more dense; the Dead Sea, for instance, had a specific gravity of 1211 ; 1000 parts of sea water contained from 22 to 28 parts of muriate of soda, and from 8 to 13 parts of other salts, which were chiefly soluble at high temperatures except the sulphate and carbonate of lime, which averaged together four-tenths of a part in every 1000 of sea water. Common salt containing from 94 to 96 parts ot muriate of soda, and from 4 to 6 parts of other salts in 100 of dry salt. Sea salt contained from 72 to 77 parts of muriate ot soda, and from 18 to 13 parts of other salts in 100 of dry salt; in the experiments from which the results of the paper were derived, a saturated solution of common salt had a specific gravity of 1213, or 77 ot the hydrometer, and 100 parts of pure water dissolved very nearly 40 parts of salt at 60 , whereas a saturated solution of sea salt had a specific gravity of 1236 or 85 of the hydrometer for the same weight (40 parts) dissolved in 100 of water—but these experiments were not necessarily constant, because the constituent parts of sea salt varied—the greater the proportion of muriate of soda the less was the specific gravity for the same weight of salt in the solution. The following were the results of the experiment: " The per centage of salt in a solution was in direct proportion to its density. The time required to obtain a given degree of concen tration was directly as the departure of the original density from concentration, the capacity of the boiler, and the relative volume of steam. And inversely as the density of the feed water, the capacity of the cylinder, and the velocity of motion. As regarded time, it was preferable to employ a low pressure, as the time consumed in arriving at a given concentration was longer as the pressure was lower. In equal weights of salt dissolved in equal weights ot water, the more heterogeneous the salts the greater was the density they exhibited in solution. The excess of temperature of the water of any solution, above that of the steam generated from it, whether below or aDove atmospheric pressure, was constant for any solution whatever might be the pressure and the temperature of the steam. The excess being in direct proportion to the quantity of salt dissolved by a constant weight of water. The expansion of any solution, in the excess of the expansion of pure water, was in direct proportion to the salt dissolved by a constant weight of water. It was also ascertained that the water spaces ot boilers should be small and the feed water as hot as possible to save fuel, and the density of feed water should be kept as low as possible."
This article was originally published with the title "Experiments upon the Use or Salt-water in Steam Boilers"