This is one of the few books which philosophy2 has condescended to give mankind for the improvement of the lower arts. The performance is indeed rather useful than pleasing, sometimes obscured by the use of terms, which none but bleachers understand, and sometimes made unpleasing to an English ear, by words and phrases never uttered on this side of the Tweed.3 But the author wrote for his countrymen, and his business was rather to instruct than to delight. It had yet been proper to have told the meaning of words peculiar to the trade on which he treats, but we seldom suspect others of ignorance in things which daily use has made familiar to ourselves. Our author talks of pulling cloth, as a seaman mentions “starboard” and “larboard,” and perhaps both would be alike astonished to find that their hearers do not understand them.4

The history of a piece of linen cloth from the loom to the market is very minutely delivered, and may justly excite curiosity as every man is immediately or remotely interested in the process, we shall therefore deliver it in the author’s words without presuming to alter what perhaps we do not always fully comprehend. . . .5

In the following sections Dr. Home relates very curious experiments made upon all the substances used in bleaching; this narrative has every token of fairness and caution; one objection he might easily have obviated. His measures are not always determinate, he mentions too frequently spoonfuls, and tea-spoonfuls, by which the reader cannot be very nicely informed of the quantity intended. The error indeed cannot be great in these cases, nor of great importance, but accuracy is always desirable.6

In the second section of the fourth part he undertakes a subject yet more generally important than the former. He endeavours to investigate the cause and remedy of hard water.

The hardness of water has been hitherto commonly imputed to sea salt latent in it, though in quantities too small to be perceived by the taste.8

To soften hard water many methods have been proposed. Water softens to the taste by being boiled. Dr. Home therefore tried various degrees of heat upon water, but it still continued hard; he at last boiled eight pints to one, but it was then much harder than before.9

Hard water kept long exposed to heat in a state of stagnation is supposed to soften. Four pints of hard water were therefore kept before a kitchen fire from July the fifth to November the eleventh, it was then found reduced to half, wholly free from corruption, but twice as hard as before; that is, it required twice as much soft water as at first to be mingled with it, before it would completely mix with soap. Dung added to it to produce a putrefaction did not soften it, but flesh and fish putrified in it, made it quite soft.1

An attempt was made to soften water by filtering it through sand, which at first succeeded, but the matter that makes water hard made its way through the sand, in twenty-four hours, and then the filtration had no effect.2

Water filtered through chalk becomes soft, but passes too slowly to afford any useful quantity. Chalk mixed with water does not soften it. Water poured upon lime is not softened. Nor do extracts of vegetables soften water.3

Water is softened only by alkaline salts. Pearl ashes,4 and spirit of hartshorn soften water.5

It is not sea salt but the bittern6 of sea salt that makes water hard; pure salt dissolved in it does not harden it, but the fourth part of a grain of bittern salt hardened a spoonful of rain water.7

The great discoverer of hard water is oleum tartari per deliquium,8 which will make it lactescent9 even when it will not curdle soap, but produces no change in water completely soft. The most subtle discoverer of salt in water is a solution of quicksilver in aqua-fortis, of which a few drops will produce a milky colour when only a single grain of salt is mixed with three pints.1

The common Epsom salt of the chymists is only the sea salt with bittern. Alum, salt of steel, and blue vitriol harden water. . . .2

The sum of this discourse, which is indeed of great importance, is this. For many uses soft water is necessary, but it is not every where afforded by nature; it is therefore sometimes requisite to soften hard water, which may be done by burning any herbs or wood, and throwing the ashes into the water.