NOTICE OF THE LIFE OF MR. WATT. HIS FRIENDS AND ASSOCIATES AT BIRMINGHAM.INVENTION OF THE COPYING PRESS. HEATING BY STEAM. - DRYING LINEN BY STEAM. THEORY OF THE COMPOSITION OF WATER. FIRST MARRIAGE OF WATT. DEATH OF HIS FIRST WIFE, HIS SECOND MARRIAGE. DEATH OF HIS YOUNGER SON. EXTRACTS FROM HIS LETTERS. CHARACTER OF WATT BY LORD BROUGHAM. BY SIR WALTER SCOTT BY LORD JEFFREY.OCCUPATION OF HIS OLD AGE. INVENTION OF MACHINE FOR COPYING SCULPTURE. HIS LAST DAYS.- MONUMENTS.

(179.) HAVING brought this historical analysis of the invention and application of the steam engine to the date of the decease of the illustrious man, to the powers of whose mind

mankind by that machine, it will perhaps not be deemed an improper digression in this work, to devote some pages to a notice of the principal labours of the same mind in other departments of art and science, and to circumstances connected with his personal history and the close of his life, which cannot fail to possess general interest.

At the period when Watt, having connected himself in partnership with Boulton, went to reside at Soho, near Birmingham, a number of persons, some of whom have since attained great celebrity by their discoveries and their works, and all of whom were devoted to inquiries connected with the arts and sciences, resided in that neighbourhood. Among these may be mentioned PRIESTLEY, whose discoveries in physical science have rendered his name immortal; DARWIN, the philosopher and poet; WITHERING, a distinguished physician and botanist; KEIR, a chemist, who published a translation of Macquer, with annotations; GALTON, the ornithologist; and EDGEWORTH, whose investigations respecting wheeled carriages and other subjects, have rendered him well known. A society was formed by these and other individuals, of which Boulton and Watt were leading members, the meetings of which were held monthly on the evening of full moon, and which was thence called the Lunar Society. At the meetings of this society, subjects connected with the arts and sciences were discussed, and out of those discussions occasionally arose suggestions not unattended with important and advantageous consequences. At one of these meetings, Darwin stated that he had discovered a pen formed with two quills, by means of which, at a single operation, an original and a copy of a letter might be produced. Watt almost instantly observed that he thought he could find a better expedient, and that he would turn it in his mind that night. By the next morning the COPYING PRESS was invented, for which he afterwards obtained a pa

tent.

This machine, which is now so generally used in countinghouses, consists of a rolling-press, by which a leaf of thin paper, previously damped, is pressed upon the letter to be copied. The writing, of which the ink is not yet quite dry, leaves its impression upon the thin paper thus pressed upon

it, and the copy taken in this manner is read through the semi-transparent paper. If a letter be written with ink suitable for this purpose, a copy may be taken at any time within several hours after the letter is written.

The method of heating apartments and buildings by steam, which has since been improved and brought into extensive use, was likewise brought forward by Watt. Although this contrivance had been previously pointed out by Sir Hugh Platt about the middle of the seventeenth century, and by Colonel Cooke in 1745, yet these suggestions remained barren. Mr. Watt gave detailed methods of heating buildings by steam*; and also invented a machine for drying linen by steam, a description of which he communicated to Dr. Brewster, which was read in December, 1824, before the Society for promoting Useful Arts in Scotland.+

But the circumstance, exclusive of those connected with the invention of the steam engine, which is by far the most memorable in the career of Watt, is the share which he had in the discovery of the composition of water. As this circumstance has recently excited much interest, and led to some controversy, we shall here state, as distinctly as possible, the leading facts connected with it.

Water, which was so long held to be a simple element, has, in modern times, been proved to be a substance consisting of two aeriform bodies or gases chemically combined. These two gases are those called in chemistry oxygen and hydrogen. If eight grains weight of oxygen be mixed with one grain weight of hydrogen, and the mixture be submitted to such effects as would cause the chemical combination of these two airs, it would be converted into nine grains weight of pure water.

If, on the other hand, nine grains weight of pure water be submitted to any conditions which would separate its constituent parts, the result would be eight grains weight of oxygen gas, and one grain weight of hydrogen gas. There are a variety of methods in physics by which these effects would be

* See Buchanan on the Economy of Fuel and Management of Heat, especially as it relates to heating and drying by means of Steam.

See Brewster's Edinburgh Encyclopædia, article STEAM-DRYING

produced. It will be sufficient here to state one method of producing each of the above changes.

If eight grains weight of oxygen be inclosed in a strong vessel with one grain weight of hydrogen, all other substances being excluded, and the mixture be inflamed, an explosion will take place, the gases will disappear, and a small quantity of water will be the only substance remaining in the vessel. If this water be weighed, it will be found to weigh exactly nine grains.

It is known that the metals have a strong attraction for oxygen gas, and this attraction is promoted by elevating their temperature. If a glass tube be filled with iron wire heated to redness, and to one end of this tube a small vessel of boiling water be attached, the steam evolved from the water will force its way through the spaces between the red-hot wires in the tube, and would be expected to issue from the remote end; but if the substance issuing from the remote end of the tube be examined, it will be found to be not steam, but hydrogen gas. If the quantity of this gas be ascertained by weight, and also the quantity of weight lost by the vessel of water at the other end of the tube, it will be found that the loss of weight of the water by evaporation will be nine times the weight of the hydrogen which has issued from the remote end of the tube. If the weight of the tube with the wire contained in it be next ascertained, it will be found to be increased by eight times the weight of the hydrogen which has issued from its remote end. From this it follows that the weight of the hydrogen which has escaped from the tube, added to the increase of weight which has been given to the wire in the tube, makes up the whole weight of the water evaporated. If the wire in the tube be next examined, it will be found that it has suffered oxydation, or, in other words, that a new substance has been formed in it called the oxyde of iron, —such substance being a chemical compound formed of oxygen gas and iron.

It follows, therefore, that in this process the vapour of the water, in passing through the tube, has been decomposed, and that, having given up to the iron its oxygen, the hydrogen

alone escaped from the other end; and for every nine grains weight of steam which passed through the tube, eight grains of oxygen have been combined with the iron, and one grain of hydrogen has escaped from the end of the tube.

Such are the class of effects on which the modern discovery of the composition of water has been based. The merit of that discovery has been shared between the celebrated English chemist, CAVENDISH, and the not less celebrated French chemist, LAVOISIER, the chief merit, however, being ascribed to the former.

We shall now briefly state the facts which led to this discovery, with their dates, which will necessarily show the share which Watt had in it.

When pure hydrogen gas is burned in an atmosphere of common air, the process which takes place is now known to be nothing more than the chemical combination of the hydrogen with eight times its own weight of oxygen taken from the atmosphere, and the product of the combustion is a quantity of water nine times the weight of the hydrogen consumed. In the year 1776, Macquer, a well-known chemist of that day, having held a saucer of white porcelain over a flame of hydrogen which was burning at the mouth of a bottle, observed that no smoke was produced and no soot deposited on the saucer. On the other hand, he found that after the lapse of some time drops of a clear pellucid liquid were perceptible on the saucer: this liquid he submitted to analysis, and found it to be pure water. Macquer mentioned this fact without comment or inference. It did not occur to him that the water thus produced upon the saucer was a substance which contained the hydrogen, which disappeared upon combustion from the bottle.

On the 18th of April, 1781, Mr. Warltire addressed a letter to Dr. Priestley, dated Birmingham, which letter is published in Dr. Priestley's Experiments on Air, printed at Birmingham in 1781, in which Warltire informs Priestley that he had fired a mixture of hydrogen and common air in close glass vessels, and that, although previously to firing the mixture the vessels were clean and dry, a dewy deposit was

X