This method, however, of blowing out furnishes but a partial remedy for the evils we have alluded to: a loose deposite will perhaps be removed by such means, but an incrustation, more or less according to the circumstances and quality of the water, will be formed; besides which, the temptation to work the vessel with efficiency for the moment influences the engine men to neglect blowing out; and it is found that this class of persons can rarely be relied upon to resort to this remedy with that constancy and regularity which are essential for the due preservation of the boilers. The class of steam vessels which, at present, are exposed to the greatest injury from these causes are the sea-going steamers employed by the Admiralty; and we find, by a report made by Messrs. Lloyd and Kingston to the Admiralty, in August, 1834, that it is admitted that the method of blowing out is, even when daily attended to, ineffectual. "The water in the boiler," these gentlemen observe, "is kept from exceeding a certain degree of saltness, by periodically blowing a portion of it into the sea; but whatever care is taken, in long voyages especially, salt will accumulate, and sometimes in great quantities and of great hardness, so that it is with difficulty it can be removed. Boilers are thus often injured as much in a few months as they would otherwise be in as many years. The other evil necessarily resulting from this state of things is, besides the rapid destruction of the boilers, a great waste of fuel, occasioned by the difficulty with which the heat passes through the incrustation on the inside, by the leaks which are thereby caused, and by the practice of blowing out periodically, as before mentioned, a considerable portion of the boiling water."
It would be impracticable to carry on board the vessel a sufficient quantity of pure fresh water to work the engine exclusively by its means. To accomplish this, it would be necessary to have a sufficient supply of cold water to keep the condensing cistern cold, to supply the jet in the condenser, and to have a reservoir in which the warm water coming from the waste pipe of the cold cistern might be allowed to cool. Engineers have therefore directed their attention to some method by which the steam may be condensed without a jet, and after condensation be preserved for the purpose of feeding the boiler. If this could be accomplished, it would not be necessary to provide a greater quantity of pure water than would be sufficient to make up the small portion of waste which might proceed from leakage and from other causes; and it is evident that this portion might always be readily obtained by the distillation of sea water, which might be effected by a small vessel exposed to the same fire which acts upon the boiler.