THE AIRO-HYDROGEN BLOWPIPE.

455

In soldering by the autogenous process, the works are first prepared and scraped clean as usual, the hydrogen is ignited, and the size of the flame is proportioned by the stop-cock h; the air is then admitted through a, until the flame assumes a fine pointed character, with which the work is united after the Fig. 314.

general method of blowpipe soldering, except that a strip of lead is used instead of solder, and generally without any flux.

This mode is described as being suitable to most of the metals, but its best application appears to be to plumber's work, and it has been adopted for such in our government dock-yards. The weight of lead consumed in making the joints, is a mere fraction of the weight of ordinary solder, which is both more expensive and more oxidizable, from the tin it contains. The gas soldering, as it is called, removes likewise the risk of accidents from the plumbers' fires, as the gas generator, which is itself harmless, may be allowed to remain on the ground whilst the workman ascends to the roof, or elsewhere, with the pipe.

Lead is interposed as solder in uniting, zinc to zinc, and it is also used in soldering the brass nozzles and cocks to the vessels of lead, and of copper coated with lead, used as generators.

Another very practical application of the gas flame, is for keeping

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THE AIRO HYDROGEN BLOWPIPE.

the copper soldering tool, fig. 315, at one temperature, which is done by leading the mixed gases through a tube in the handle, so that the flame plays on the back of the copper bit. This mode seems to be very well adapted to tin-plate and zinc works, especially as the common street gas may be used, thereby dispensing with the necessity for the gas generator, the construction and management of which alone remain to be explained.

The gas generator, fig. 314, bears some resemblance to Pepys' gazometer. When it is first charged, the stopper 1, is unscrewed, and the lower chamber is nearly filled with curly shreds of sheet zinc, and the stopper is replaced. The cover is now removed, and a plug with a long wire is inserted from the top into the hole near 3; the upper chamber is next filled with dilute sulphuric acid, (1 acid and 6 water,) until it is just seen through the central hole to rise above the plate immediately beneath it. This measures the quantity of liquid required to charge the vessel without the risk of overflow. The plug is now withdrawn from 3, and the cocks 4, and h, being opened, the air escapes from the lower vessel by the pressure of the column of water which enters beneath the perforated bottom 5, upon which the zinc rests. The cocks 4 and h are now closed, and by the decomposition of the water hydrogen is generated, which occupies the upper part of the lower chamber, and drives the dilute acid upwards, through the aperture 3, so as to place matters in the position of the engraving, which represents the generator about two-thirds filled with gas.

The gas issues through the pipe h, when both cocks are opened, but it has to proceed through a safety box 6, in which the syphon tube, dips two or three inches into a little plain water introduced at the lateral aperture 7; by this precaution the contents of the gazometer cannot be ignited, as should the flame return through the pipe h, it would be intercepted by the water in the safety box. After three or four days' constant work the liquid becomes converted into the sulphate of zinc, and is withdrawn through the plug 8; the vessel is then refilled with fresh dilute acid as already explained, but the zinc lasts a considerable time.

The generators are made of lead, or where portability and lightness are required, of copper washed with lead, and all the exposed parts of the brass work are washed and united with lead to defend them from the acid. Occasionally the air is likewise

supplied by aerometers, or vessels somewhat resembling the gas generator, but which are only filled with common air, and therefore do not require the zinc or acid*.

THE great and unintended length to which the pages of the present volume have extended, is to be solely attributed to a constant desire to set forth in sufficient detail, the general principles and features of the numerous subjects which have been considered. In the fulfilment of this task, I have been induced very greatly to enlarge upon the original manuscript during its passage through the press, by the notice and explanation of additional illustrations, many of which have been indeed acquired during that period.

Yet notwithstanding this great extension, it may be satisfactorily added, that this has in no respect led to any departure from the arrangement first proposed in pages 10 to 12, of the introductory chapter; as all the processes forming the subject matter of the foregoing sheets, are accomplished nearly without the use of cutting tools, and are such as could not, consistently with the plan of this work, be so well placed elsewhere.

* The following is the broad difference between the airo-hydrogen and the oxyhydrogen blowpipes. In the oxy-hydrogen blowpipe, the pure gases are mixed in the exact proportions of two volumes of hydrogen to one of oxygen, which quantities when combined constitute water, and in this particular case there is the greatest condensation of volume, and the greatest evolution of latent as well as of sensible heat.

The airo-hydrogen blowpipe, is supplied with common air and with pure hydrogen; this instrument is also the most effective when the oxygen and hydrogen are mixed in the proportions of 1 to 2; but the nitrogen, which constitutes four-fifths of our atmosphere, is now in the way and detracts from the intensity of the effect.

END OF THE FIRST VOLUME.

APPENDIX.

During the period in which this Volume has been passing through the press, some new matters having relation to its pages have been published; a few of these are here noticed, and by the insertion of the references in the body of the work, these Notes will come under observation in their appropriate places.

Note A.-To follow the end of Page 46.

The Patent Wood Carving. This is not accomplished in the usual manner, by cutting away the wood with chisels, but it is burned away, or rather converted into charcoal. The oak, mahogany, rose-wood, horse-chesnut, or other wood, is steeped in water for about two hours; and the cast-iron die or mould containing the device, is heated to redness or sometimes to a white heat, and applied against the wood; either by a handle as a branding-iron, by a lever-press, or by a screw-press, according to circumstances; the moulds are made by the iron-founder from plaster casts of the original models or carvings.

Had not the wood been saturated with water it would be ignited, but until the moisture is evaporated it is only charred; it gives off volumes of smoke, but no flame. After a short time the iron is returned to the furnace to be re-heated, the blackened wood is well rubbed with a hard brush to remove the charcoal powder, which, being a bad conductor of heat, saves the wood from material discoloration; and before the re-application of the heated iron the wood is again soaked in water, but for a shorter time, as it now absorbs moisture with more facility.

The rotation of burning, brushing, and wetting is repeated ten or twenty times or upwards, until in fact the wood fills every cavity in the mould, the process being materially influenced by the character and condition of the wood itself, and the degrees in which the heat and moisture are applied. The water so far checks the destruction of the wood, or even its change of any kind, that the burned surface simply cleaned by brushing, is often employed, as it may be left either of a very pale or deep brown, according to the tone of colour required, so as to match old carvings of any age; or a very little scraping removes the discoloured surface. Perforated carvings are burned upon thick blocks of wood, and cut off with the circular saw.

The patent mode is considerably cheaper than ordinary carving, and the more so the greater the complexity and delicacy of the design. The date of the Patent granted to Messrs. A. S. Braithwaite and Co. for this novel process is Nov. 1840.,

Note B.-To follow the Foot Note on Page 116.

Subsequently to the extract from "Dr. Boucherie's Memoir on the Preservation of Woods" having been printed upon page 113-116 of this work, the subject came under the notice of the Institution of Civil Engineers; and in justice to the prior claim of Mr. Bethell, I have quoted the following paragraphs from the Minutes of Proceedings of that Institution for 1842, page 88-9.

"Mr. Bethell remarked that the process described in Dr. Boucherie's pamphlet was identical with that patented by him July 11th, 1838, two years before Dr. Boucherie's was mentioned in Paris, which was in June 1840. The specification